Most of the work we do with athletes regarding sports nutrition is to teach them and their coaches how to structure their diet and time food intake to optimize performance and recovery. Dietary supplements can play a meaningful role in helping athletes consume the proper amount of calories, carbohydrate, and protein in their diet. However, they should be viewed as supplements to the diet, not replacements for a good diet. While it is true that most dietary supplements available for athletes have little scientific data supporting their potential role to enhance training and/or performance, it is also true that a number of nutrients and/or dietary supplements have been shown to help improve performance and/or recovery. Supplementation with these nutrients can help augment the normal diet to help optimize performance. Sports nutrition specialists must be aware of the current data regarding nutrition, exercise, and performance and be honest about educating their clients about results of various studies (whether pro or con). With the proliferation of information available about nutritional supplements to the consumer, the sports nutrition specialist, nutritionist, and nutrition industry lose credibility when they do not accurately describe results of various studies to the public. The following outlines several classifications of nutritional supplements that are often taken by athletes and categorizes them into 'apparently effective', 'possibly effective', 'too early to tell', and 'apparently ineffective' supplements based on interpretation of the literature. It should be noted that this analysis focuses primarily on whether the proposed nutrient has been found to affect exercise and/or training adaptations based on the current available literature. Additional research may or may not reveal ergogenic value, possibly altering its classification. It should be also noted that although there may be little ergogenic value to some nutrients, there may be some potential health benefits that may be helpful for some populations. Therefore, just because a nutrient does not appear to affect performance and/or training adaptations, that does not mean it does not have possible health benefits for athletes.

Convenience Supplements

Convenience supplements are meal replacement powders (MRP's), ready to drink supplements (RTD's), energy bars, and energy gels. They currently represent the largest segment of the dietary supplement industry representing 50 - 75% of most company's sales. They are typically fortified with vitamins and minerals and differ on the amount of carbohydrate, protein, and/or fat they contain. They may also vary based whether they are fortified with various nutrients purported to promote weight gain, enhance weight loss, and/or improve performance. Most people view these supplements as a nutrient dense snack and/or use them to help control caloric intake when trying to gain and/or lose weight. In our view, MRP's, RTD's, and energy bars/gels can provide a convenient way for people to meet specific dietary needs and/or serve as good alternatives to fast food other foods of lower nutritional value. Use of these types of products can be particularly helpful in providing carbohydrate, protein, and other nutrients prior to and/or following exercise in an attempt to optimize nutrient intake when an athlete doesn't have time to sit down for a good meal or wants to minimize food volume. However, they should be used to improve dietary availability of macronutrients - not as a replacement for a good diet. Care should also be taken to make sure they do not contain any banned or prohibited nutrients.

Muscle Building Supplements

The following provides an analysis of the literature regarding purported weight gain supplements and our general interpretation of how they should be categorized based on this information. Table 3 summarizes how we currently classify the ergogenic value of a number of purported performance-enhancing, muscle building, and fat loss supplements based on an analysis of the available scientific evidence.

Table 3 Summary of categorization of dietary supplements based on available literature. Full size table

Apparently Effective

Weight Gain Powders

One of the most common means athletes have employed to increase muscle mass is to add extra calories to the diet. Most athletes "bulk up" in this manner by consuming extra food and/or weight gain powders. In order to increase skeletal muscle mass, there must be adequate energy intake (anabolic reactions are endergonic and therefore require adequate energy intake). Studies have consistently shown that simply adding an extra 500 - 1,000 calories per day to your diet in conjunction with resistance training will promote weight gain [31, 33]. However, only about 30 - 50% of the weight gained on high calorie diets is muscle while the remaining amount of weight gained is fat. Consequently, increasing muscle mass by ingesting a high calorie diet can help build muscle but the accompanying increase in body fat may not be desirable for everyone. Therefore, we typically do not recommend this type of weight gain approach [39].

Creatine monohydrate

In our view, the most effective nutritional supplement available to athletes to increase high intensity exercise capacity and muscle mass during training is creatine monohydrate. Numerous studies have indicated that creatine supplementation increases body mass and/or muscle mass during training [70] Gains are typically 2 - 5 pounds greater than controls during 4 - 12 weeks of training [71]. The gains in muscle mass appear to be a result of an improved ability to perform high intensity exercise enabling an athlete to train harder and thereby promote greater training adaptations and muscle hypertrophy [72–75]. The only clinically significant side effect occasionally reported from creatine monohydrate supplementation has been the potential for weight gain [71, 76–78] Although concerns have been raised about the safety and possible side effects of creatine supplementation [79, 80], recent long-term safety studies have reported no apparent side effects [78, 81, 82] and/or that creatine monohydrate may lessen the incidence of injury during training [83–85]. Additionally a recent review was published which addresses some of the concerns and myths surrounding creatine monohydrate supplementation [86]. Consequently, supplementing the diet with creatine monohydrate and/or creatine containing formulations seems to be a safe and effective method to increase muscle mass. The ISSN position stand on creatine monohydrate [87] summarizes their findings as this:

1. Creatine monohydrate is the most effective ergogenic nutritional supplement currently available to athletes in terms of increasing high-intensity exercise capacity and lean body mass during training. 2. Creatine monohydrate supplementation is not only safe, but possibly beneficial in regard to preventing injury and/or management of select medical conditions when taken within recommended guidelines. 3. There is no compelling scientific evidence that the short- or long-term use of creatine monohydrate has any detrimental effects on otherwise healthy individuals. 4. If proper precautions and supervision are provided, supplementation in young athletes is acceptable and may provide a nutritional alternative to potentially dangerous anabolic drugs. 5. At present, creatine monohydrate is the most extensively studied and clinically effective form of creatine for use in nutritional supplements in terms of muscle uptake and ability to increase high-intensity exercise capacity. 6. The addition of carbohydrate or carbohydrate and protein to a creatine supplement appears to increase muscular retention of creatine, although the effect on performance measures may not be greater than using creatine monohydrate alone. 7. The quickest method of increasing muscle creatine stores appears to be to consume ~0.3 grams/kg/day of creatine monohydrate for at least 3 days followed by 3-5 g/d thereafter to maintain elevated stores. Ingesting smaller amounts of creatine monohydrate (e.g., 2-3 g/d) will increase muscle creatine stores over a 3-4 week period, however, the performance effects of this method of supplementation are less supported. 8. Creatine monohydrate has been reported to have a number of potentially beneficial uses in several clinical populations, and further research is warranted in these areas.

Protein

As previously described, research has indicated that people undergoing intense training may need additional protein in their diet to meet protein needs (i.e., 1.4 - 2.0 grams/day [13, 39] . People who do not ingest enough protein in their diet may exhibit slower recovery and training adaptations [33]. Protein supplements offer a convenient way to ensure that athletes consume quality protein in the diet and meet their protein needs. However, ingesting additional protein beyond that necessary to meet protein needs does not appear to promote additional gains in strength and muscle mass. The research focus over recent years has been to determine whether different types of protein (e.g., whey, casein, soy, milk proteins, colostrum, etc) and/or various biologically active protein subtypes and peptides (e.g., α-lactalbumin, β-lactoglobulin, glycomacropeptides, immunoglobulins, lactoperoxidases, lactoferrin, etc) have varying effects on the physiological, hormonal, and/or immunological responses to training [88–91]. In addition, a significant amount of research has examined whether timing of protein intake and/or provision of specific amino acids may play a role in protein synthesis and/or training adaptations, conducted mostly in untrained populations [92–105]. Although more research is necessary in this area, evidence clearly indicates that protein needs of individuals engaged in intense training are elevated, different types of protein have varying effects on anabolism and catabolism, that different types of protein subtypes and peptides have unique physiological effects, and timing of protein intake may play an important role in optimizing protein synthesis following exercise. Therefore, it is simplistic and misleading to suggest that there is no data supporting contentions that athletes need more protein in their diet and/or there is no potential ergogenic value of incorporating different types of protein into the diet. It is the position stand of ISSN that exercising individuals need approximately 1.4 to 2.0 grams of protein per kilogram of bodyweight per day. This is greater than the RDA recommendations for sedentary individuals. According to the current literature we know that the addition of protein and or BCAA before or after resistance training can increase protein synthesis and gains in lean mass beyond normal adaptation. However, it should be noted that gains have primarily been observed in untrained populations unless the supplement contained other nutrients like creatine monohydrate [13, 39].

Essential Amino Acids (EAA)

Recent studies have indicated that ingesting 3 to 6 g of EAA prior to [105, 106] and/or following exercise stimulates protein synthesis [92, 93, 98–101, 105]. Theoretically, this may enhance gains in muscle mass during training. To support this theory, a study by Esmarck and colleagues [107] found that ingesting EAA with carbohydrate immediately following resistance exercise promoted significantly greater training adaptations in elderly, untrained men, as compared to waiting until 2-hours after exercise to consume the supplement. Although more data is needed, there appears to be strong theoretical rationale and some supportive evidence that EAA supplementation may enhance protein synthesis and training adaptations. Because EAA's include BCAA's, it is probable that positive effects on protein synthesis from EAA ingestion are likely due to the BCAA content [108, 109]. Garlick and Grant [109] infused glucose into growing rats to achieve a concentration of insulin secretion that was insufficient to stimulate protein synthesis by itself. In addition to this, all eight essential amino acids with glucose was infused into another group and then in a third group the investigators only infused the BCAA's along with the glucose. Compared with the glucose infusion alone, protein synthesis was stimulated equally by the essential amino acids and the BCAAs. This demonstrates that the BCAAs are the key amino acids that stimulate protein synthesis. The ISSN position stand on protein concluded that BCAAs have been shown to acutely stimulate protein synthesis, aid in glycogen resynthesis, delaying the onset of fatigue, and help maintain mental function in aerobic-based exercise. It was concluded that consuming BCAAs (in addition to carbohydrates) before, during, and following an exercise bout would be recommended safe and effective [39].

Possibly Effective

β-hydroxy β-methylbutyrate (HMB)

HMB is a metabolite of the amino acid leucine. Leucine and metabolites of leucine have been reported to inhibit protein degradation [110]. Supplementing the diet with 1.5 to 3 g/d of calcium HMB during training has been typically reported to increase muscle mass and strength particularly among untrained subjects initiating training [111–116] and the elderly [117]. Gains in muscle mass are typically 0.5 to 1 kg greater than controls during 3 - 6 weeks of training. There is also evidence that HMB may lessen the catabolic effects of prolonged exercise [118, 119] and that there may be additive effects of co-ingesting HMB with creatine [120, 121]. However, the effects of HMB supplementation in athletes are less clear. Most studies conducted on trained subjects have reported non-significant gains in muscle mass possibly due to a greater variability in response of HMB supplementation among athletes [122–124]. Consequently, there is fairly good evidence showing that HMB may enhance training adaptations in individuals initiating training. However, additional research is necessary to determine whether HMB may enhance training adaptations in trained athletes.

Branched Chain Amino Acids (BCAA)

BCAA supplementation has been reported to decrease exercise-induced protein degradation and/or muscle enzyme release (an indicator of muscle damage) possibly by promoting an anti-catabolic hormonal profile [31, 51, 125]. Theoretically, BCAA supplementation during intense training may help minimize protein degradation and thereby lead to greater gains in fat-free mass. There is some evidence to support this hypothesis. For example, Schena and colleagues [126] reported that BCAA supplementation (~10 g/d) during 21-days of trekking at altitude increased fat free mass (1.5%) while subjects ingesting a placebo had no change in muscle mass. Bigard and associates [127] reported that BCAA supplementation appeared to minimize loss of muscle mass in subjects training at altitude for 6-weeks. Finally, Candeloro and coworkers [128] reported that 30 days of BCAA supplementation (14 grams/day) promoted a significant increase in muscle mass (1.3%) and grip strength (+8.1%) in untrained subjects. A recent published abstract [129] reported that resistance trained subjects ingesting 14 grams of BCAA during 8 weeks of resistance training experienced a significantly greater gain in body weight and lean mass as compared to a whey protein supplemented group and a carbohydrate placebo group. Specifically, the BCAA group gained 2 kg of body mass and 4 kg of lean body mass. In contrast, the whey protein and carbohydrate groups both gained an additional 1 kg of body mass and 2 kg and 1 kg of lean body mass, respectively. It cannot be overstated that this investigation was published as an abstract, was conducted in a gym setting, and has not undergone the rigors of peer review at this time. Although more research is necessary, these findings suggest that BCAA supplementation may have some impact on body composition.

Too Early to Tell

α-ketoglutarate (α-KG)

α-KG is an intermediate in the Krebs cycle that is involved in aerobic energy metabolism. There is some clinical evidence that α-KG may serve as an anticatabolic nutrient after surgery [130, 131]. However, it is unclear whether α-KG supplementation during training may affect training adaptations.

α-Ketoisocaproate (KIC)

KIC is a branched-chain keto acid that is a metabolite of leucine metabolism. In a similar manner as HMB, leucine and metabolites of leucine are believed to possess anticatabolic properties [132]. There is some clinical evidence that KIC may spare protein degradation in clinical populations [133, 134]. Theoretically, KIC may help minimize protein degradation during training possibly leading to greater training adaptations. However, we are not aware of any studies that have evaluated the effects of KIC supplementation during training on body composition.

Ecdysterones

Ecdysterones (also known as ectysterone, 20 Beta-Hydroxyecdysterone, turkesterone, ponasterone, ecdysone, or ecdystene) are naturally derived phytoecdysteroids (i.e., insect hormones). They are typically extracted from the herbs Leuza rhaptonticum sp., Rhaponticum carthamoides, or Cyanotis vaga. They can also be found in high concentrations in the herb Suma (also known as Brazilian Ginseng or Pfaffia). Research from Russia and Czechoslovakia conducted over the last 30 years indicates that ecdysterones may possess some potentially beneficial physiological effects in insects and animals [135–140]. However, since most of the data on ecdysterones have been published in obscure journals, results are difficult to interpret. Wilborn and coworkers [141] gave resistance trained males 200 mg of 20-hydroxyecdysone per day during 8-weeks of resistance training. It was reported that the 20-hydroxyecdysone supplementation had no effect on fat free mass or anabolic/catabolic hormone status [141]. Due to the findings of this well controlled study in humans, ecdysterone supplementation at a dosage of 200 mg per day appears to be ineffective in terms of improving lean muscle mass. While future studies may find some ergogenic value of ecdysterones, it is our view that it is too early to tell whether phytoecdysteroids serve as a safe and effective nutritional supplement for athletes.

Growth Hormone Releasing Peptides (GHRP) and Secretagogues

Research has indicated that growth hormone releasing peptides (GHRP) and other non-peptide compounds (secretagogues) appear to help regulate growth hormone (GH) release [142, 143]. These observations have served as the basis for development of nutritionally-based GH stimulators (e.g., amino acids, pituitary peptides, "pituitary substances", Macuna pruriens, broad bean, alpha-GPC, etc). Although there is clinical evidence that pharmaceutical grade GHRP's and some non-peptide secretagogues can increase GH and IGF-1 levels at rest and in response to exercise, it has not been demonstrated that such increases lead to an increase in skeletal muscle mass [144].

Ornithine-α-ketoglutarate (OKG)

OKG (via enteral feeding) has been shown to significantly shorten wound healing time and improve nitrogen balance in severe burn patients [145, 146]. Because of its ability to improve nitrogen balance, OKG may provide some value for athletes engaged in intense training. A study by Chetlin and colleagues [147] reported that OKG supplementation (10 grams/day) during 6-weeks of resistance training promoted greater gains in bench press. However, no significant differences were observed in squat strength, training volume, gains in muscle mass, or fasting insulin and growth hormone. Therefore, additional research is needed before conclusions can be drawn.

Zinc/Magnesium Aspartate (ZMA)

The main ingredients in ZMA formulations are zinc monomethionine aspartate, magnesium aspartate, and vitamin B-6. The rationale of ZMA supplementation is based on studies suggesting that zinc and magnesium deficiency may reduce the production of testosterone and insulin like growth factor (IGF-1). ZMA supplementation has been theorized to increase testosterone and IGF-1 leading to greater recovery, anabolism, and strength during training. In support of this theory, Brilla and Conte [148] reported that a zinc-magnesium formulation increased testosterone and IGF-1 (two anabolic hormones) leading to greater gains in strength in football players participating in spring training. In another study conducted by Wilborn et al. [149], resistance trained males ingested a ZMA supplement and found no such increases in either total or free testosterone. In addition, this investigation also assessed changes in fat free mass and no significant differences were observed in relation to fat free mass in those subjects taking ZMA. The discrepancies concerning the two aforementioned studies may be explained by deficiencies of these minerals. Due to the role that zinc deficiency plays relative to androgen metabolism and interaction with steroid receptors [150], when there are deficiencies of this mineral, testosterone production may suffer. In the study showing increases in testosterone levels [148], there were depletions of zinc and magnesium in the placebo group over the duration of the study. Hence, increases in testosterone levels could have been attributed to impaired nutritional status rather than a pharmacologic effect. More research is needed to further evaluate the role of ZMA on body composition and strength during training before definitive conclusions can be drawn.

Apparently Ineffective

Glutamine

Glutamine is the most plentiful non-essential amino acid in the body and plays a number of important physiological roles [31, 108, 109] Glutamine has been reported to increase cell volume and stimulate protein [151, 152] and glycogen synthesis [153]. Despite its important role in physiological roles, there is no compelling evidence to support glutamine supplementation in terms of increasing lean body mass. One study that is often cited in support of glutamine supplementation and its role in increasing muscle mass was published by Colker and associates [154]. It was reported that subjects who supplemented their diet with glutamine (5 grams) and BCAA (3 grams) enriched whey protein during training promoted about a 2 pound greater gain in muscle mass and greater gains in strength than ingesting whey protein alone. While a 2 pound increase in lean body mass was observed, it is likely that these gains were due to the BCAAs that were added to the whey protein. In a well-designed investigation, Candow and co-workers [155] studied the effects of oral glutamine supplementation combined with resistance training in young adults. Thirty-one participants were randomly allocated to receive either glutamine (0.9 g/kg of lean tissue mass) or a maltodextrin placebo (0.9 g/kg of lean tissue mass) during 6 weeks of total body resistance training. At the end of the 6-week intervention, the authors concluded glutamine supplementation during resistance training had no significant effect on muscle performance, body composition or muscle protein degradation in young healthy adults. While there may be other beneficial uses for glutamine supplementation, there does not appear to be any scientific evidence that it supports increases in lean body mass or muscular performance.

Smilax officinalis (SO)

SO is a plant that contains plant sterols purported to enhance immunity as well as provide an androgenic effect on muscle growth [1]. Some data supports the potential immune enhancing effects of SO. However, we are not aware of any data that show that SO supplementation increases muscle mass during training.

Isoflavones

Isoflavones are naturally occurring non-steroidal phytoestrogens that have a similar chemical structure as ipriflavone (a synthetic flavonoid drug used in the treatment of osteoporosis) [156–158]. For this reason, soy protein (which is an excellent source of isoflavones) and isoflavone extracts have been investigated in the possible treatment of osteoporosis. Results of these studies have shown promise in preventing declines in bone mass in post-menopausal women as well as reducing risks to side effects associated with estrogen replacement therapy. More recently, the isoflavone extracts 7-isopropoxyisoflavone (ipriflavone) and 5-methyl-7-methoxy-isoflavone (methoxyisoflavone) have been marketed as "powerful anabolic" substances. These claims have been based on research described in patents filed in Hungary in the early 1970s [159, 160]. Aubertin-Leheudre M, et al. [161] investigated the effects that isoflavone supplementation would have on fat-free mass in obese, sarcopenic postmenopausal women. Eighteen sarcopenic-obese women ingested 70 mg of isoflavones per day (44 mg of daidzein, 16 mg glycitein and 10 mg genistein) or a placebo for six months. There was no exercise intervention in the investigation, only the isoflavone supplementation. At the end of the six month intervention, it was reported that there was no difference in total body fat free mass between the isoflavone and placebo groups, but there was a significant increase in the appendicular (arms and legs) fat free mass in the isoflavone supplemented group but not the placebo group. Findings from this study have some applications to sedentary, postmenopausal women. However, there are currently no peer-reviewed data indicating that isoflavone supplementation affects exercise, body composition, or training adaptations in physically active individuals.

Sulfo-Polysaccharides (Myostatin Inhibitors)

Myostatin or growth differentiation factor 8 (GDF-8) is a transforming growth factor that has been shown to serve as a genetic determinant of the upper limit of muscle size and growth [162]. Recent research has indicated that eliminating and/or inhibiting myostatin gene expression in mice [163] and cattle [164–166] promotes marked increases in muscle mass during early growth and development. The result is that these animals experience what has been termed as a "double-muscle" phenomenon apparently by allowing muscle to grow beyond its normal genetic limit. In agriculture research, eliminating and/or inhibiting myostatin may serve as an effective way to optimize animal growth leading to larger, leaner, and a more profitable livestock yield. In humans, inhibiting myostatin gene expression has been theorized as a way to prevent or slow down muscle wasting in various diseases, speed up recovery of injured muscles, and/or promote increases in muscle mass and strength in athletes [167]. While these theoretical possibilities may have great promise, research on the role of myostatin inhibition on muscle growth and repair is in the very early stages - particularly in humans. There is some evidence that myostatin levels are higher in the blood of HIV positive patients who experience muscle wasting and that myostatin levels negatively correlate with muscle mass [162]. There is also evidence that myostatin gene expression may be fiber specific and that myostatin levels may be influenced by immobilization in animals [168]. Additionally, a study by Ivey and colleagues [167] reported that female athletes with a less common myostatin allele (a genetic subtype that may be more resistant to myostatin) experienced greater gains in muscle mass during training and less loss of muscle mass during detraining. No such pattern was observed in men with varying amounts of training histories and muscle mass. These early studies suggest that myostatin may play a role in regulating muscle growth to some degree. Some nutrition supplement companies have marketed sulfo-polysaccharides (derived from a sea algae called Cytoseira canariensis) as a way to partially bind the myostatin protein in serum. When untrained males supplemented with 1200 mg/day of Cystoseira canariensis in conjunction with a twelve week resistance training regimen, it was reported that there were no differences between the supplemented group and the placebo group in relation to fat-free mass, muscle strength, thigh volume/mass, and serum myostatin [169]. Interestingly, a recent paper by Seremi and colleagues [170] reported that resistance training reduced serum myostatin levels and that creatine supplementation in conjunction with resistance training promoted further reductions. Nevertheless, though the research is limited, there is currently no published data supporting the use of sulfo-polysaccharides as a muscle building supplement.

Boron

Boron is a trace mineral proposed to increase testosterone levels and promote anabolism. Several studies have evaluated the effects of boron supplementation during training on strength and body composition alterations. These studies (conducted on male bodybuilders) indicate that boron supplementation (2.5 mg/d) appears to have no impact on muscle mass or strength [171, 172].

Chromium

Chromium is a trace mineral that is involved in carbohydrate and fat metabolism. Clinical studies have suggested that chromium may enhance the effects of insulin particularly in diabetic populations. Since insulin is an anti-catabolic hormone and has been reported to affect protein synthesis, chromium supplementation has been theorized to serve as an anabolic nutrient. Theoretically, this may increase anabolic responses to exercise. Although some initial studies reported that chromium supplementation increased gains in muscle mass and strength during training particularly in women [173–175], most well-controlled studies [176] that have been conducted since then have reported no benefit in healthy individuals taking chromium (200-800 mcg/d) for 4 to 16-weeks during training [177–183]. Consequently, it appears that although chromium supplementation may have some therapeutic benefits for diabetics, chromium does not appear to be a muscle-building nutrient for athletes.

Conjugated Linoleic Acids (CLA)

Animal studies indicate that adding CLA to dietary feed decreases body fat, increases muscle and bone mass, has anti-cancer properties, enhances immunity, and inhibits progression of heart disease [184–186]. Consequently, CLA supplementation in humans has been suggested to help manage body composition, delay loss of bone, and provide health benefit. Although animal studies are impressive [187–189] and some studies suggests benefit over time at some but not all dosages [190–192], there is little current evidence that CLA supplementation during training can affect lean tissue accretion [193, 194]. As will be discussed below, there appears to be more promise of CLA as a supplement to promote general health and/or reductions in fat mass over time.

Gamma Oryzanol (Ferulic Acid)

Gamma oryzanol is a plant sterol theorized to increase anabolic hormonal responses during training [195]. Although data are limited, one study reported no effect of 0.5 g/d of gamma oryzanol supplementation on strength, muscle mass, or anabolic hormonal profiles during 9-weeks of training [196].

Prohormones

Testosterone and growth hormone are two primary hormones in the body that serve to promote gains in muscle mass (i.e., anabolism) and strength while decreasing muscle breakdown (catabolism) and fat mass [197–204]. Testosterone also promotes male sex characteristics (e.g., hair, deep voice, etc) [198]. Low level anabolic steroids are often prescribed by physicians to prevent loss of muscle mass for people with various diseases and illnesses [205–216]. It is well known that athletes have experimented with large doses of anabolic steroids in an attempt to enhance training adaptations, increase muscle mass, and/or promote recovery during intense training [198–200, 203, 204, 217]. Research has generally shown that use of anabolic steroids and growth hormone during training can promote gains in strength and muscle mass [197, 202, 204, 210, 213, 218–225]. However, a number of potentially life threatening adverse effects of steroid abuse have been reported including liver and hormonal dysfunction, hyperlipidemia (high cholesterol), increased risk to cardiovascular disease, and behavioral changes (i.e., steroid rage) [220, 226–230]. Some of the adverse effects associated with the use of these agents are irreversible, particularly in women [227]. For this reason, anabolic steroids have has been banned by most sport organizations and should be avoided unless prescribed by a physician to treat an illness.

Prohormones (androstenedione, 4-androstenediol, 19-nor-4-androstenedione, 19-nor-4-androstenediol, 7-keto DHEA, and DHEA, etc) are naturally derived precursors to testosterone or other anabolic steroids. Prohormones have become popular among body builders because they believe they are natural boosters of anabolic hormones. Consequently, a number of over-the-counter supplements contain prohormones. While there is some data indicating that prohormones increase testosterone levels [231, 232], there is virtually no evidence that these compounds affect training adaptations in younger men with normal hormone levels. In fact, most studies indicate that they do not affect testosterone and that some may actually increase estrogen levels and reduce HDL-cholesterol [220, 231, 233–238]. Consequently, although there may be some potential applications for older individuals to replace diminishing androgen levels, it appears that prohormones have no training value. Since prohormones are "steroid-like compounds", most athletic organizations have banned their use. Use of nutritional supplements containing prohormones will result in a positive drug test for anabolic steroids. Use of supplements knowingly or unknowingly containing prohormones have been believed to have contributed to a number of recent positive drug tests among athletes. Consequently, care should be taken to make sure that any supplement an athlete considers taking does not contain prohormone precursors particularly if their sport bans and tests for use of such compounds. It is noteworthy to mention that many prohormones are not lawful for sale in the USA since the passage of the Anabolic Steroid Control Act of 2004. The distinctive exception to this is DHEA, which has been the subject of numerous clinical studies in aging populations.

Rather than provide the body with a precursor to testosterone, a more recent technique to enhance endogenous testosterone has been to inhibit aromatase activity [239]. Two studies have investigated the effects of aromatase inhibitors (androst-4-ene-3,6,17-trione) [240] and (hydroxyandrost-4-ene-6,17-dioxo-3-THP ether and 3,17-diketo-androst-1,4,6-triene) [241]. In both of these investigations, it was reported that free testosterone and dihydrotesterone levels were significantly increased. Muscle mass/fat free mass was not measured in one investigation [240] and no changes were observed in fat free mass in the other investigation [241].

Tribulus terrestris

Tribulus terrestris (also known as puncture weed/vine or caltrops) is a plant extract that has been suggested to stimulate leutinizing hormone (LH) which stimulates the natural production of testosterone [132]. Consequently, Tribulus has been marketed as a supplement that can increase testosterone and promote greater gains in strength and muscle mass during training. Several recent studies have indicated that Tribulus supplementation appears to have no effects on body composition or strength during training [242–244].

Vanadyl Sulfate (Vanadium)

In a similar manner as chromium, vanadyl sulfate is a trace mineral that has been found to affect insulin-sensitivity and may affect protein and glucose metabolism [132, 245]. For this reason, vanadyl sulfate has been purported to increase muscle mass and strength during training. Although there may be some clinical benefits for diabetics (with a therapeutic dose of at least 50 mg vanadyl sulfate twice daily [246, 247], vanadyl sulfate supplementation does not appear to have any effect on strength or muscle mass during training in non-diabetic, weight training individuals [248, 249].

Weight Loss Supplements

Although exercise and proper diet remain the best way to promote weight loss and/or manage body composition, a number of nutritional approaches have been investigated as possible weight loss methods (with or without exercise). The following overviews the major types of weight loss products available and discusses whether any available research supports their use. See Table 3 for a summary.

Apparently Effective

Low Calorie Diet Foods & Supplements

Most of the products in this category represent low fat/carbohydrate, high protein food alternatives [250]. They typically consist of pre-packaged food, bars, MRP, or RTD supplements. They are designed to provide convenient foods/snacks to help people follow a particular low calorie diet plan. In the scientific literature, diets that provide less than 1000 calories per day are known as very low calorie diets (VLCD's). Pre-packaged food, MRP's, and/or RTD's are often provided in VLCD plans to help people cut calories. In most cases, VLCD plans recommend behavioural modification and that people start a general exercise program.

Research on the safety and efficacy of people maintaining VLCD's generally indicate that they can promote weight loss. For example, Hoie et al [251] reported that maintaining a VLCD for 8-weeks promoted a 27 lbs (12.6%) loss in total body mass, a 21 lbs loss in body fat (23.8%), and a 7 lbs (5.2%) loss in lean body mass in 127 overweight volunteers. Bryner and colleagues [252] reported that addition of a resistance training program while maintaining a VLCD (800 kcal/d for 12-weeks) resulted in a better preservation of lean body mass and resting metabolic rate compared to subjects maintaining a VLCD while engaged in an endurance training program. Meckling and Sherfey [253] reported that the combination of high protein and exercise was the most effective intervention for weight loss and was superior to a low-fat, high-carbohydrate diet in promoting weight loss and nitrogen balance regardless of the presence of an exercise intervention. Recent studies indicate that high protein/low fat VLCD's may be better than high carbohydrate/low fat diets in promoting weight loss [46, 253–260]. The reason for this is that typically when people lose weight about 40-50% of the weight loss is muscle which decreases resting energy expenditure. Increasing protein intake during weight loss helps preserve muscle mass and resting energy expenditure to a better degree than high carbohydrate diets [261, 262]. These findings and others indicate that VLCD's (typically using MRP's and/or RTD's as a means to control caloric intake) can be effective particularly as part of an exercise and behavioural modification program. Most people appear to maintain at least half of the initial weight lost for 1-2 years but tend to regain most of the weight back within 2-5 years. Therefore, although these diets may help people lose weight on the short-term, it is essential people who use them follow good diet and exercise practices in order to maintain the weight loss. The addition of dietary protein whether in whole food form or meal replacement form could assist in this weight maintenance due to the fact that the retention of muscle mass is greater than in high carbohydrate/low-fat weight loss trials?

Ephedra, Caffeine, and Silicin

Thermogenics are supplements designed to stimulate metabolism thereby increasing energy expenditure and promote weight loss. They typically contain the "ECA" stack of ephedra alkaloids (e.g., Ma Haung, 1R,2S Nor-ephedrine HCl, Sida Cordifolia), caffeine (e.g., Gaurana, Bissey Nut, Kola) and aspirin/salicin (e.g., Willow Bark Extract). The first of the three traditional thermogenics is now banned by the FDA however the safety associated with the ingestion of ephedra is debated. More recently, other potentially thermogenic nutrients have been added to various thermogenic formulations. For example, thermogenic supplements may also contain synephrine (e.g., Citrus Aurantum, Bitter Orange), calcium & sodium phosphate, thyroid stimulators (e.g., guggulsterones, L-tyrosine, iodine), cayenne & black pepper, and ginger root.

A significant amount of research has evaluated the safety and efficacy of EC and ECA type supplements. According to a meta-analysis in the Journal of American Medical Association, ephedrine/ephedra promote a more substantial weight loss 0.9 kg per month in comparison to placebo in clinical trials but are associated with increased risk of psychiatric, autonomic or gastrointestinal symptoms as well as heart palpitations. Several studies have confirmed that use of synthetic or herbal sources of ephedrine and caffeine (EC) promote about 2 lbs of extra weight loss per month while dieting (with or without exercise) and that EC supplementation is generally well tolerated in healthy individuals [263–274]. For example, Boozer et al [267] reported that 8-weeks of ephedrine (72 mg/d) and caffeine (240 mg/d) supplementation promoted a 9 lbs loss in body mass and a 2.1% loss in body fat with minor side effects. Hackman and associates [275] reported that a 9 month clinical trial utilizing a multi-nutrient supplement containing 40 mg/d of ephedra alkaloids and 100 mg/day caffeine resulted in a loss of weight and body fat, improved metabolic parameters including insulin sensitivity without any apparent side effects. Interestingly, Greenway and colleagues [274] reported that EC supplementation was a more cost-effective treatment for reducing weight, cardiac risk, and LDL cholesterol than several weight loss drugs (fenfluramine with mazindol or phentermine). Finally, Boozer and associates [268] reported that 6-months of herbal EC supplementation promoted weight loss with no clinically significant adverse effects in healthy overweight adults. Less is known about the safety and efficacy of synephrine, thyroid stimulators, cayenne/black pepper and ginger root.

Despite these findings, the Food and Drug Administration (FDA) banned the sale of ephedra containing supplements. The rationale has been based on reports to adverse event monitoring systems and in the media suggesting a link between intake of ephedra and a number of severe medical complications (e.g., high blood pressure, elevated heart rate, arrhythmias, sudden death, heat stroke, etc) [276, 277]. Although results of available clinical studies do not show these types of adverse events, ephedra is no longer available as an ingredient in dietary supplements and thus cannot be recommended for use. Consequently, thermogenic supplements now contain other nutrients believed to increase energy expenditure (e.g., synephrine, green tea, etc) and are sold as "ephedrine-free" types of products. Anyone contemplating taking thermogenic supplements should carefully consider the potential side effects, discuss possible use with a knowledgeable physician, and be careful not to exceed recommended dosages.

Possibly Effective

High Fiber Diets

One of the oldest and most common methods of suppressing the appetite is to consume a diet that is high in fiber. Ingesting high fiber foods (fruits, vegetables) or fiber containing supplements (e.g., glucomannan) increase the feeling of fullness (satiety) which typically allows an individual to feel full while ingesting fewer calories. Theoretically, maintaining a high fiber diet may serve to help decrease the amount of food you eat. In addition, high fiber diets/supplements help lower cholesterol and blood pressure, enhance insulin sensitivity, and promote weight loss in obese subjects [278]. A recent study found that a Mediterranean diet that was high in fiber resulted in a more dramatic weight loss that a traditional low-fat diet and had beneficial effects on glycemic control [279]. Other research on high fiber diets indicates that they provide some benefit, particularly in diabetic populations. For example, Raben et al [280] reported that subjects maintaining a low fat/high fiber diet for 11 weeks lost about 3 lbs of weight and 3.5 lbs of fat. Other studies have reported mixed results on altering body composition using various forms of higher fiber diets [281–284]. Consequently, although maintaining a low fat/high fiber diet that is high in fruit and vegetable content has various health benefits, these diets seem to have potential to promote weight loss as well as weight maintenance thus we can recommend high fiber diets as a safe and healthy approach to possibly improve body composition.

Calcium

Several studies and recent reviews have reported that calcium supplementation alone or in combination with other ingredients does not affect weight loss or fat loss [285–290]. Research has indicated that calcium modulates 1,25-diydroxyvitamin D which serves to regulate intracellular calcium levels in fat cells [291, 292]. Increasing dietary availability of calcium reduces 1,25-diydroxyvitamin D and promotes reductions in fat mass in animals [292–294]. Dietary calcium has been shown to suppress fat metabolism and weight gain during periods of high caloric intake [291, 293, 295]. Further, increasing calcium intake has been shown to increase fat metabolism and preserve thermogenesis during caloric restriction [291, 293, 295]. In support of this theory, Davies and colleagues [296] reported that dietary calcium was negatively correlated to weight and that calcium supplementation (1,000 mg/d) accounted for an 8 kg weight loss over a 4 yr period. Additionally, Zemel and associates [291] reported that supplemental calcium (800 mg/d) or high dietary intake of calcium (1,200 - 1,300 mg/d) during a 24-week weight loss program promoted significantly greater weight loss (26-70%) and dual energy x-ray absorptiometer (DEXA) determined fat mass loss (38-64%) compared to subjects on a low calcium diet (400-500 mg/d). These findings and others suggest a strong relationship between calcium intake and fat loss. However, more research needs to be conducted before definitive conclusions can be drawn.

Green Tea Extract

Green tea is now one of the most common herbal supplements that is being added to thermogenic products because it has been suggested to affect weight loss and is now the fourth most commonly used dietary supplement in the US [297]. Green tea contains high amounts of caffeine and catechin polyphenols. The primary catechin that is associated to the potential effects on weight loss through diet induced thermogenesis is the catechin epigallocatechin gallate, also known as EGCG [298, 299]. Research suggests that catechin polyphenols possess antioxidant properties and the intake of tea catechins is associated with a reduced risk of cardiovascular disease [298–300]. In addition, green tea has also been theorized to increase energy expenditure by stimulating brown adipose tissue thermogenesis. In support of this theory, Dulloo et al [301, 302] reported that green tea supplementation in combination with caffeine (e.g., 50 mg caffeine and 90 mg epigallocatechin gallate taken 3-times per day) significantly increased 24-hour energy expenditure and fat utilization in humans to a much greater extent than when an equivalent amount of caffeine was evaluated suggesting a synergistic effect. Recently, work by Di Pierro and colleagues [303] reported that the addition of a green tea extract to a hypocaloric diet resulted in a significant increase in weight loss (14 kg vs. 5 kg) versus a hypocaloric diet alone over a 90 day clinical trial. Maki and coworkers [304] also demonstrated that green tea catechin consumption enhanced the exercise-induced changes in abdominal fat. However, it must be noted that both human and animal studies have not supported these findings and have reported that supplementation of these extracts does not affect weight loss [305, 306]. Theoretically, increases in energy expenditure may help individuals lose weight and/or manage body composition.

Conjugated Linoleic Acids (CLA)

CLA is a term used to describe a group of positional and geometric isomers of linoleic acid that contain conjugated double bonds. Adding CLA to the diet has been reported to possess significant health benefits in animals [184, 307]. In terms of weight loss, CLA feedings to animals have been reported to markedly decrease body fat accumulation [185, 308]. Consequently, CLA has been marketed as a health and weight loss supplement since the mid 1990s. Despite the evidence in animal models, the effect of CLA supplementation in humans is less clear. There are some data suggesting that CLA supplementation may modestly promote fat loss and/or increases in lean mass [190–192, 309–314]. Recent work suggested that CLA supplementation coupled with creatine and whey protein resulted in a increase in strength and lean-tissue mass during resistance training [315]. However, other studies indicate that CLA supplementation (1.7 to 12 g/d for 4-weeks to 6-months) has limited to no effects on body composition alterations in untrained or trained populations [190, 310, 316–324]. The reason for the discrepancy in research findings has been suggested to be due to differences in purity and the specific isomer studied. For instance, early studies in humans showing no effect used CLA that contained all 24 isomers. Today, most labs studying CLA use 50-50 mixtures containing the trans-10, cis-12 and cis-9, trans-11 isomers, the former of which being recently implicated in positively altering body composition. This has been supported by recent work indicating that CLA (50:50 cis-9, trans-11:trans-10, cis-12) plus polyunsaturated fatty acid supplementation prevented abdominal fat increases and increase fat-free mass [325]. However, it must be noted that this response only occurred in young obese individuals. Thus, CLA supplementation may have potential in the areas of general health and it is clear that research on the effects on body composition is ongoing and still quite varied. Further research is needed to determine which CLA isomer is ideal for ingestion and possibly if there are differential responses among lean or obese and old or young populations.

Too Early to Tell

Gymnema Sylvestre

Gymnema Sylvestre is a supplement that is purported to regulate weight loss and blood sugar levels. It is purported to affect glucose and fat metabolism as well as inhibit sweet cravings. In support of these contentions, some recent data have been published by Shigematsu and colleagues [326, 327] showing that short and long-term oral supplementation of gymnema sylvestre in rats fed normal and high-fat diets may have some positive effects on fat metabolism, blood lipid levels, and/or weight gain/fat deposition. More recent work in rats has shown that gymnema sylvestre supplementation promoted weight loss by reducing hyperlipidemia [328]. The only apparent clinical trial in humans showed that an herbal combination group containing 400 mg of gymnema sylvestra resulted in effective and safe weight loss while promoting improved blood lipid profiles. It should be noted that this group was not significantly different that the other active group, containing HCA, when observing these dependent variables [329]. Due to the lack of substantial positive research on the effects of gymnema sylvestre supplementation in humans, we cannot recommend gymnema sylvestre as a supplement to positively affect weight loss.

Phosphatidyl Choline (Lecithin)

Choline is considered an essential nutrient that is needed for cell membrane integrity and to facilitate the movement of fats in and out of cells. It is also a component of the neurotransmitter acetylcholine and is needed for normal brain functioning, particularly in infants. For this reason, phosphatidyl choline (PC) has been purported as a potentially effective supplement to promote fat loss as well as improve neuromuscular function. However, despite these alleged benefits of lecithin supplementation, there are no clinical trials in humans to support a potential role of lecithin supplementation affecting weight loss.

Betaine

Betaine is a compound that is involved in the metabolism of choline and homocysteine. Garcia Neto et al. [330] have shown that betaine feedings can effect liver metabolism, fat metabolism, and fat deposition in chickens. Betaine supplementation may also help lower homocysteine levels which is a marker of risk to heart disease [331]. For this reason, betaine supplements have been marketed as a supplement designed to promote heart health as well as a weight loss. A recent study by Hoffman and colleagues [332] found betaine supplementation to improve muscular endurance in active college age males. Despite this, there appears to be little evidence in human models that supports the role of betaine as a supplement for weight loss and thus it is not recommended for supplementation.

Coleus Forskohlii (Forskolin)

Forskolin, which is touted as a weight loss supplement is a plant native to India that has been used for centuries in traditional Ayurvedic medicine primarily to treat skin disorders and respiratory problems [333, 334]. A considerable amount of research has evaluated the physiological and potential medical applications of forskolin over the last 25 years. Forskolin has been reported to reduce blood pressure, increase the hearts ability to contract, help inhibit platelet aggregation, improve lung function, and aid in the treatment of glaucoma [333–335]. With regard to weight loss, forskolin has been reported to increase cyclic AMP and thereby stimulate fat metabolism [336–338]. Theoretically, forskolin may therefore serve as an effective weight loss supplement. Recent evidence has shown that forskolin supplementation had no effect on improving body composition in mildly obese women [339]. In contrast, work done by Godard et al. in 2005 reported that 250 mg of a 10% forskolin extract taken twice daily resulted in improvements in body composition in overweight and obese men [340]. Another study suggested that supplementing the diet with coleus forskohlii in overweight women helped maintain weight and was not associated with any clinically significant adverse events [341]. Currently, research is still needed on forskolin supplementation before it can be recommended as an effective weight loss supplement.

Dehydroepiandrosterone (DHEA) and 7-Keto DHEA

Dehydroepiandrosterone (DHEA) and its sulfated conjugate DHEAS represent the most abundant adrenal steroids in circulation [342]. Although, DHEA is considered a weak androgen, it can be converted to the more potent androgens testosterone and dihydrotestosterone in tissues. In addition, DHEAS can be converted into androstenedione and testosterone. DHEA levels have been reported to decline with age in humans [343]. The decline in DHEA levels with aging has been associated with increased fat accumulation and risk to heart disease [344]. Since DHEA is a naturally occurring compound, it has been suggested that dietary supplementation of DHEA may help maintain DHEA availability, maintain and/or increase testosterone levels, reduce body fat accumulation, and/or reduce risk to heart disease as one ages [342, 344]. Although animal studies have generally supported this theory, the effects of DHEA supplementation on body composition in human trials have been mixed. For example, Nestler and coworkers [345] reported that DHEA supplementation (1,600 mg/d for 28-d) in untrained healthy males promoted a 31% reduction in percentage of body fat. However, Vogiatzi and associates [346] reported that DHEA supplementation (40 mg/d for 8 wks) had no effect on body weight, percent body fat, or serum lipid levels in obese adolescents. More recent work has supported these findings suggesting that one year of DHEA supplementation had no effect on body composition when taken at 50 mg per day [347]. 7-keto DHEA, a DHEA precursor, has been marketed as a potentially more effective form of DHEA which is believed to possess lypolytic properties. Although data are limited, Kalman and colleagues and coworkers [348] reported that 7-keto DHEA supplementation (200 mg/d) during 8-weeks of training promoted a greater loss in body mass and fat mass while increasing T3 while observing no significant effects on thyroid stimulating hormone (TSH) or T4. More recent data has shown that 7-keto DHEA supplementation can increase RMR [349] and blunt the decrease in RMR associated with 8 weeks of restricted dieting [350]. However, it must be noted that the second study did not use isolated 7-keto DHEA but used a commercial weight loss product that contained DHEA as well as other known weight loss agents (i.e. caffeine, green tea extract, citrus aurantium, etc.). Thus, these results do not directly support the use of 7-keto DHEA. Although more research is needed on the effects of supplementing DHEA by itself as a weight loss agent, these findings provide minimal support that 7-keto DHEA may serve as an effective weight loss supplement.

Psychotropic Nutrients/Herbs

Psychotropic nutrients/herbs are a new class of supplements that often contain things like St. John's Wart, Kava, Ginkgo Biloba, Ginseng, and L-Tyrosine. They are believed to serve as naturally occurring antidepressants, relaxants, and mental stimulants thus the theoretical rationale regarding weight loss is that they may help people fight depression or maintain mental alertness while dieting. There are no clinical weight loss trials that utilize any of the above nutrients/herbs as the active ingredient in the supplementation trial. Although a number of studies support potential role as naturally occurring psychotropics or stimulants, the potential value in promoting weight loss is unclear and therefore are not recommended for supplementation.

Apparently Ineffective

Calcium Pyruvate

Calcium Pyruvate is supplement that hit the scene about 10-15 ago with great promise. The theoretical rationale was based on studies from the early 1990s that reported that calcium pyruvate supplementation (16 - 25 g/d with or without dihydroxyacetone phosphate [DHAP]) promoted fat loss in overweight/obese patients following a medically supervised weight loss program [351–353]. Although the mechanism for these findings was unclear, the researchers speculated that it might be related to appetite suppression and/or altered carbohydrate and fat metabolism. Since calcium pyruvate is very expensive, several studies have attempted to determine whether ingesting smaller amounts of calcium pyruvate (6-10 g/d) affect body composition in untrained and trained populations. Results of these studies are mixed. Earlier studies have shown both a positive effect on calcium pyruvate supplementation in improving body composition [354], however, Stone and colleagues [355] reported that pyruvate supplementation did not affect hydrostatically determined body composition during 5-weeks of in-season college football training. More recently, calcium pyruvate supplementation was also shown to not have a significant effect on body composition or exercise performance. Additionally, it has been reported that supplementation may negatively affect some blood lipid levels [356]. These findings indicate that although there is some supportive data indicating that calcium pyruvate supplementation may enhance fat loss when taken at high doses (6-16 g/d), there is no evidence that ingesting the doses typically found in pyruvate supplements (0.5 - 2 g/d) has any affect on body composition. In addition, the overall quantity of research examining calcium pyruvate is minimal at best thus it is not warranted to include calcium pyruvate as a weight loss supplement.

Chitosan

Chitosan has been marketed as a weight loss supplement for several years as is known as a "fat trapper". It is purported to inhibit fat absorption and lower cholesterol. This notion is supported animal studies indicated by decreased fat absorption, increased fat content, and/or lower cholesterol following chitosan feedings [357–360]. However, the effects in humans appear to be less impressive. For example, although there is some data suggesting that chitosan supplementation may lower blood lipids in humans,[361] other studies report no effects on fat content [362, 363]or body composition alterations [364–366] when administered to people following their normal diet. More recent work has shown that the effect of chitosan on fat absorption is negligible and is the equivalent of approximately 9.9 kcal/day following supplementation [362]. Other work has concluded that the insignificant amounts of fat that are trapped from supplementation would take about 7 months for a male to lose a pound of weight, and that the effect was completely ineffective in women [364]. Thus, based on the current evidence, chitosan supplementation is apparently ineffective and has no significant effects on "fat trapping" and/or on improving body composition.

Chromium

Chromium supplementation is derived from its role in maintaining proper carbohydrate and fat metabolism by potentially effecting insulin signalling [367]. Initial studies reported that chromium supplementation during resistance training improved fat loss and gains in lean body mass [173–175]. To date, the studies using more accurate methods of assessing body composition have primarily indicate no effects on body composition in healthy non-diabetic individuals [176–183, 368]. Recent work has reported that 200 mcg of chromium picolinate supplementation on individuals on a restrictive diet did not promote weight loss or body composition changes following 12 weeks of supplementation [368]. This work supports Lukaski et al [182] previous findings that 8-weeks of chromium supplementation during resistance training did not affect strength or DEXA determined body composition changes. Thus, based on the current review of the literature we cannot recommend chromium supplementation as a means of improving body composition.

Garcinia Cambogia (HCA)

HCA is a nutrient that has been hypothesized to increase fat oxidation by inhibiting citrate lypase and lipogenesis [369]. Theoretically, this may lead to greater fat burning and weight loss over time. Although there is some evidence that HCA may increase fat metabolism in animal studies, there is little to no evidence showing that HCA supplementation affects body composition in humans. For example, Ishihara et al [370] reported that HCA supplementation spared carbohydrate utilization and promoted lipid oxidation during exercise in mice. However, Kriketos and associates [371] reported that HCA supplementation (3 g/d for 3-days) did not affect resting or post-exercise energy expenditure or markers of lipolysis in healthy men. Likewise, Heymsfield and coworkers [372] reported that HCA supplementation (1.5 g/d for 12-weeks) while maintaining a low fat/high fiber diet did not promote greater weight or fat loss than subjects on placebo. Finally, Mattes and colleagues [373] reported that HCA supplementation (2.4 g/d for 12-weeks) did not affect appetite, energy intake, or weight loss. These findings suggest that HCA supplementation does not appear to promote fat loss in humans.

L-Carnitine

Carnitine serves as an important transporter of fatty acids from the cytosol into the mitochondria of the cell [374]. Increased cellular levels of carnitine would theoretically enhance transport of fats into the mitochondria and thus provide more substrates for fat metabolism. L-carnitine has been one of the most common nutrients found in various weight loss supplements. Over the years, a number of studies have been conducted on the effects of L-carnitine supplementation on fat metabolism, exercise capacity and body composition. The overwhelming conclusions of L-carnitine research indicates that L-carnitine supplementation does not affect muscle carnitine content [375], fat metabolism, aerobic- or anaerobic-exercise performance [375], and/or weight loss in overweight or trained subjects [376, 377]. Despite the fact that L-carnitine has been shown apparently ineffective as a supplement, the research on L-carnitine has shifted to another category revolving around hypoxic stress and oxidative stress. Preliminary research has reported that L-carnitine supplementation has a minimal effect on reducing the biomarkers of exercise-induced oxidative stress [378]. While these findings are not promising, there is some recent data indicating that L-carnitine tartrate supplementation during intensified periods of training may help athletes tolerate training to a greater degree [379]. Consequently, there may be other advantages to L-carnitine supplementation than promoting fat metabolism.

Phosphates

The role of sodium and calcium phosphate on energy metabolism and exercise performance has been studied for decades [31]. Phosphate supplementation has also been suggested to affect energy expenditure, however, the research in this area is quite dated and no research on the effects on energy expenditure have been conducted. Some of this dated work includes the work by Kaciuba-Uscilko and colleagues [380] who reported that phosphate supplementation during a 4-week weight loss program increased resting metabolic rate (RMR) and respiratory exchange ratio (suggesting greater carbohydrate utilization and caloric expenditure) during submaximal cycling exercise. In addition, Nazar and coworkers [381] reported that phosphate supplementation during an 8-week weight loss program increased RMR by 12-19% and prevented a normal decline in thyroid hormones. Although the rate of weight loss was similar in this trial, results suggest that phosphate supplementation may influence metabolic rate possibly by affecting thyroid hormones. Despite these to dated trials, no further research has been conducted and thus the role of phosphates in regards to weight loss is inconclusive at best.

Herbal Diuretics

This is a new type of supplement recently marketed as a natural way to promote weight loss. There is limited evidence that taraxacum officinale, verbena officinalis, lithospermum officinale, equisetum arvense, arctostaphylos uva-ursi, arctium lappa and silene saxifraga infusion may affect diuresis in animals [382, 383]. Two studies presented at the 2001 American College of Sports Medicine meeting [384, 385] indicated that although herbal diuretics promoted a small amount of dehydration (about 0.3% in one day), they were not nearly as effective as a common diuretic drug (about 3.1% dehydration in one day). Consequently, although more research is needed, the potential value of herbal diuretics as a weight loss supplement appears limited.

Performance Enhancement Supplements

A number of nutritional supplements have been proposed to enhance exercise performance. Some of these nutrients have been described above. Table 3 categorizes the proposed ergogenic nutrients into apparently safe and effective, possibly effective, too early to tell, and apparently ineffective. Weight gain supplements purported to increase muscle mass may also have ergogenic properties if they also promote increases in strength. Similarly, some sports may benefit from reductions in fat mass. Therefore, weight loss supplements that help athletes manage body weight and/or fat mass may also possess some ergogenic benefit. The following describes which supplements may or may not affect performance that were not previously described.

Apparently Effective

Water and Sports Drinks

Preventing dehydration during exercise is one of the keys of maintaining exercise performance (particularly in hot/humid environments). People engaged in intense exercise or work in the heat need to frequently ingest water or sports drinks (e.g., 1-2 cups every 10 - 15 minutes). The goal should be not to lose more than 2% of body weight during exercise (e.g., 180 lbs × 0.02 = 3.6 lbs). Sports drinks typically contain salt and carbohydrate at scientifically engendered quantities. Studies show that ingestion of sports drinks during exercise in hot/humid environments can help prevent dehydration and improve endurance exercise capacity [[56], von Duvillard 2005), [386, 387]]. In fact, research has shown that carbohydrate intake during team sport type activities can increase exercise performance and CNS function [15, 16, 388]. Consequently, frequent ingestion of water and/or sports drinks during exercise is one of the easiest and most effective ergogenic aids.

Carbohydrate

One of the best ergogenic aids available for athletes and active individuals alike, is carbohydrate. Athletes and active individuals should consume a diet high in carbohydrate (e.g., 55 - 65% of calories or 5-8 grams/kg/day) in order to maintain muscle and liver carbohydrate stores [1, 3]. Research has clearly identified carbohydrate is an ergogenic aid that can prolong exercise [3]. Additionally, ingesting a small amount of carbohydrate and protein 30-60 minutes prior to exercise and use of sports drinks during exercise can increase carbohydrate availability and improve exercise performance. Finally, ingesting carbohydrate and protein immediately following exercise can enhance carbohydrate storage and protein synthesis [1, 3].

Creatine

Earlier we indicated that creatine supplementation is one of the best supplements available to increase muscle mass and strength during training. However, creatine has also been reported to improve exercise capacity in a variety of events [[71], Kendall 2005, [389–391]]. This is particularly true when performing high intensity, intermittent exercise such as multiple sets of weight lifting, repeated sprints, and/or exercise involving sprinting and jogging (e.g., soccer) [71]. Creatine has also been shown to be effective at improving high intensity interval training. A 2009 study found that in addition to high intensity interval training creatine improved critical power [390]. Although studies evaluating the ergogenic value of creatine on endurance exercise perfor mance are mixed, endurance athletes may also theoretically benefit in several ways. For example, increasing creatine stores prior to carbohydrate loading (i.e., increasing dietary carbohydrate intake before competition in an attempt to maximize carbohydrate stores) has been shown to improve the ability to store carbohydrate [392–394]. A 2003 study found that ingesting 20 grams of creatine for 5 days improved endurance and anaerobic performance in elite rowers [395]. Further, co ingesting creatine with carbohydrate has been shown to optimize creatine and carbohydrate loading [396]. Most endurance athletes also perform interval training (sprint or speed work) in an attempt to improve anaerobic threshold. Since creatine has been reported to enhance interval sprint performance, creatine supplementation during training may improve training adaptations in endurance athletes [397, 398]. Finally, many endurance athletes lose weight during their competitive season. Creatine supplementation during training may help people maintain weight.

Sodium Phosphate

We previously mentioned that sodium phosphate supplementation may increase resting energy expenditure and therefore could serve as a potential weight loss nutrient. However, most research on sodium phosphate has actually evaluated the potential ergogenic value. A number of studies indicated that sodium phosphate supplementation (e.g., 1 gram taken 4 times daily for 3-6 days) can increase maximal oxygen uptake (i.e., maximal aerobic capacity) and anaerobic threshold by 5-10% [399–403]. These finding suggest that sodium phosphate may be highly effective in improving endurance exercise capacity. In addition to endurance enhancement, sodium phosphate loading improved mean power output and oxygen uptake in trained cyclist in a 2008 study [404]. Other forms of phosphate (i.e., calcium phosphate, potassium phosphate) do not appear to possess ergogenic value.

Sodium Bicarbonate (Baking Soda)

During high intensity exercise, acid (H+) and carbon dioxide (CO 2 ) accumulate in the muscle and blood. One of the ways you get rid of the acidity and CO 2 is to buffer the acid and CO 2 with bicarbonate ions. The acid and CO 2 are then removed in the lungs. Bicarbonate loading (e.g., 0.3 grams per kg taken 60-90 minutes prior to exercise or 5 grams taken 2 times per day for 5-days) has been shown to be an effective way to buffer acidity during high intensity exercise lasting 1-3 minutes in duration [405–408]. This can improve exercise capacity in events like the 400 - 800 m run or 100 - 200 m swim [409]. In elite male swimmers sodium bicarbonate supplementation significantly improved 200 m freestyle performance [410]. A 2009 study found similar improvements in performance in youth swimmers at distances of 50 to 200 m. Although bicarbonate loading can improve exercise, some people have difficulty with their stomach tolerating bicarbonate as it may cause gastrointestinal distress.

Caffeine

Caffeine is a naturally derived stimulant found in many nutritional supplements typically as gaurana, bissey nut, or kola. Caffeine can also be found in coffee, tea, soft drinks, energy drinks, and chocolate. It has previously been made clear that caffeine can have a positive effect on energy expenditure, weight loss, and body fat. Caffeine has also been shown to be an effective ergogenic aid. Research investigating the effects of caffeine on a time trial in trained cyclist found that caffeine improved speed, peak power, and mean power [411]. Similar results were observed in a recent study that found cyclists who ingested a caffeine drink prior to a time trial demonstrated improvements in performance [412, 413]. Studies indicate that ingestion of caffeine (e.g., 3-9 mg/kg taken 30 - 90 minutes before exercise) can spare carbohydrate use during exercise and thereby improve endurance exercise capacity [406, 414]. In addition to the apparent positive effects on endurance performance, caffeine has also been shown to improve repeated sprint performance benefiting the anaerobic athlete [415, 416]. People who drink caffeinated drinks regularly, however, appear to experience less ergogenic benefits from caffeine [417]. Additionally, some concern has been expressed that ingestion of caffeine prior to exercise may contribute to dehydration although recent studies have not supported this concern [414, 418, 419]. Caffeine doses above 9 mg/kg can result in urinary caffeine levels that surpass the doping threshold for many sport organizations. Suggestions that there is no ergogenic value to caffeine supplementation is not supported by the preponderance of available scientific studies.

β-alanine

In recent years research has begun investigating the effects of β-alanine supplementation on performance. β-alanine has ergogenic potential based on its relationship with carnosine. Carnosine is a dipeptide comprised of the amino acids, histidine and β-alanine naturally occurring in large amounts in skeletal muscles. Carnosine is believed to be one of the primary muscle-buffering substances available in skeletal muscle. Studies have demonstrated that taking β-alanine orally over a 28-day period was effective in increasing carnosine levels [420, 421]. This proposed benefit would increase work capacity and decrease time to fatigue. Researchers have found that β-alanine supplementation decreases rate of fatigue [422]. This could translate into definite strength gains and improved performance. A recent study [423] supplemented men with β-alanine for 10 weeks and showed that muscle carnosine levels were significantly increased after 4 and 10 weeks of β-alanine supplementation.

Stout et al. [422] conducted a study that examined the effects of β-alanine supplementation on physical working capacity at fatigue threshold. The results showed decreased fatigue in the subjects tested. Other studies have shown that β-alanine supplementation can increase the number of repetitions one can do [424], increased lean body mass [425], increase knee extension torque [426] and training volume [427]. In fact, one study also showed that adding β-alanine supplementation with creatine improves performance over creatine alone [428]. While it appears that β-alanine supplementation can decrease fatigue rate, raise carnosine levels, and improve performance all of the research is not as favorable. There are other studies that show no performance benefits [425, 429]

Possibly Effective

Post-Exercise Carbohydrate and Protein

Ingesting carbohydrate and protein following exercise enhances carbohydrate storage and protein synthesis. Theoretically, ingesting carbohydrate and protein following exercise may lead to greater training adaptations. In support of this theory, Esmarck and coworkers [107] found that ingesting carbohydrate and protein immediately following exercise doubled training adaptations in comparison to waiting until 2-hours to ingest carbohydrate and protein. Additionally, Tarnopolsky and associates [430] reported that post-exercise ingestion of carbohydrate with protein promoted as much strength gains as ingesting creatine with carbohydrate during training. A recent study by Kreider and colleagues [431] found that protein and carbohydrate supplementation post workout was capable of positively supporting the post exercise anabolic response. In the last few years many studies have agreed with these findings in that post workout supplementation is vital to recovery and training adaptations [13, 104, 431–433]. These findings underscore the importance of post-exercise carbohydrate and protein ingestion to support muscle anabolism and strength. However, it is still unclear if there are direct implications of protein/carbohydrate supplementation on other markers of performance such as time to exhaustion, maximal oxygen uptake, and/or skill development.

Essential Amino Acids (EAA)

Ingestion of 3-6 grams of EAA following resistance exercise has been shown to increase protein synthesis [92, 93, 98–102, 105, 434]. Theoretically, ingestion of EAA after exercise should enhance gains in strength and muscle mass during training. While there is sound theoretical rationale, it is currently unclear whether following this strategy would lead to greater training adaptations and/or whether EAA supplementation would be better than simply ingesting carbohydrate and a quality protein following exercise.

Branched Chain Amino Acids (BCAA)

Ingestion of BCAA (e.g., 6-10 grams per hour) with sports drinks during prolonged exercise would theoretically improve psychological perception of fatigue (i.e., central fatigue). Although there is strong rationale, the effects of BCAA supplementation on exercise performance is mixed with some studies suggesting an improvement and others showing no effect [33]. More research is needed before conclusions can be drawn.

β-HMB

HMB supplementation has been reported to improve training adaptations in untrained individuals initiating training as well as help reduce muscle breakdown in runners. Theoretically, this should enhance training adaptations in athletes. However, most studies show little benefit of HMB supplementation in athletes. A 2004 study by Hoffman [435] found HMB supplementation to be ineffective in collegiate football players after short term supplementation. It has been hypothesized that HMB will delay or prevent muscle damage; however this has limited evidence as suggested in previous sections. There are a few studies that have been positive [115]. A 2009 study found that HMB supplementation did positively affect strength in trained men [436]. While HMB supplementation may still have some scientific rationale there is little evidence that is can directly affect performance in moderately trained subjects.

Glycerol

Ingesting glycerol with water has been reported to increase fluid retention [437]. Theoretically, this should help athletes prevent dehydration during prolonged exercise and improve performance particularly if they are susceptible to dehydration. Although studies indicate that glycerol can significantly enhance body fluid, results are mixed on whether it can improve exercise capacity [69, 438–443]. Little research has been done on glycerol in the last five years however, a 2006 study agreed with previous findings in that glycerol has little impact on performance [444].

Too Early to Tell

A number of supplements purported to enhance performance and/or training adaptation fall under this category. This includes the weight gain and weight loss supplements listed in Table 3 as well as the following supplements not previously described in this category.

Medium Chain Triglycerides (MCT)

MCT's are shorter chain fatty acids that can easily enter the mitochondria of the cell and be converted to energy through fat metabolism [445]. Studies are mixed as to whether MCT's can serve as an effective source of fat during exercise metabolism and/or improve exercise performance [445–449]. A 2001 study found that 60 g/day of MCT oil for two weeks was not sufficient at improving performance [450]. In fact Goedecke found that not only did MCT supplementation not improve performance, but, actually negatively affected sprint performance in trained cyclists [451]. These findings have been confirmed by others that MCT oils are not sufficient to induce positive training adaptations and may cause gastric distress [452, 453]. It must be noted that while most studies have not been favourable, one 2009 study found that MCT oil may positively affect RPE and lactate clearance [454]. It does not appear likely that MCT can positively affect training adaptations, but further research is needed.

Apparently Ineffective

Glutamine

As described above, glutamine has been shown to influence protein synthesis and help maintain the immune system. Theoretically, glutamine supplementation during training should enhance gains in strength and muscle mass as well as help athletes tolerate training to a better degree. Although there is some evidence that glutamine supplementation with protein can improve training adaptations, more research is needed to determine the ergogenic value in athletes. There is currently no research to suggest that glutamine has a direct effect on performance.

Ribose

Ribose is a 3-carbon carbohydrate that is involved in the synthesis of adenosine triphosphate (ATP) in the muscle (the useable form of energy). Clinical studies have shown that ribose supplementation can increase exercise capacity in heart patients [455–459]. For this reason, ribose has been suggested to be an ergogenic aid for athletes. Although more research is needed, most studies show no ergogenic value of ribose supplementation on exercise capacity in health untrained or trained populations [460–462]. A 2006 study [463] investigated the effects of ribose vs. dextrose on rowing performance. After eight weeks of supplementation dextrose had a better response than ribose across the subjects [463]. Kreider and associates [462] and Kersick and colleagues [464] investigated ribose supplementation on measures of anaerobic capacity in trained athletes. This research group found that ribose supplementation did not have a positive impact on performance [462, 464]. It appears at this point that ribose supplementation does not improve aerobic or anaerobic performance.

Inosine

Inosine is a building block for DNA and RNA that is found in muscle. Inosine has a number of potentially important roles that may enhance training and/or exercise performance [465]. Although there is some theoretical rationale, available studies indicate that inosine supplementation has no apparent affect on exercise performance capacity [466–468].

Supplements to Promote General Health

In addition to the supplements previously described, several nutrients have been suggested to help athletes stay healthy during intense training. For example, the American Medical Association recently recommended that all Americans ingest a daily low-dose multivitamin in order to ensure that people get a sufficient amount of vitamins and minerals in their diet. Although one-a-day vitamin supplementation has not been found to improve exercise capacity in athletes, it may make sense to take a daily vitamin supplement for health reasons. Glucosomine and chondroitin have been reported to slow cartilage degeneration and reduce the degree of joint pain in active individuals which may help athletes postpone and/or prevent joint problems [469, 470]. Supplemental Vitamin C, glutamine, echinacea, and zinc have been reported to enhance immune function [471–474]. Consequently, some sports nutritionists recommend that athletes who feel a cold coming on take these nutrients in order to enhance immune function [55, 471–473]. Similarly, although additional research is necessary, Vitamin E, Vitamin C, selenium, alpha-lipoic acid and other antioxidants may help restore overwhelmed anti-oxidant defences exhibited by athletes and reduce the risk of numerous chronic diseases in some instances [475]. Creatine, calcium β-HMB, BCAA, and L-carnitine tartrate have been shown to help athletes tolerate heavy training periods [31, 118, 125, 126, 128, 379, 476–478]. Finally, the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapantaenoic acid (EPA), in supplemental form, are now endorsed by the American Heart Association for heart health in certain individuals [479]. This supportive supplement position stems from: 1.) an inability to consume cardio-protective amounts by diet alone; and, 2.) the mercury contamination sometimes present in whole-food sources of DHA and EPA found in fatty fish. Consequently, prudent use of these types of nutrients at various times during training may help athletes stay healthy and/or tolerate training to a greater degree [50].