Body composition

The observation that resistance exercise in combination with a low carbohydrate diet resulted in reduced body weight and body fat as compared with similar exercise while on a regular diet is in accordance with previous studies showing a large loss of weight and body fat when carbohydrate intake is reduced and maintained at a low level [34–37, 42–48].

This study do not clarify whether the observed results can be attributed to energy restriction in general or to carbohydrate restriction per se. Whatever the mechanisms might be, the subjects in the Lc+Ex group reduced body fat while maintaining lean body mass. Similar results have also been obtained using resistance exercise in combination with a regular energy restricted diet [27]. However, a decreased feeling of hunger seems to be an advantage with the low carbohydrate diet [49–51], an effect attributed to increased levels of ketone bodies [50], reduced levels of neuropeptide Y and leptin levels and decreased insulin levels [1]. Carbohydrate restriction will reduce glucose availability and lower insulin output, and may increase the concentration of counter regulatory hormones such as catecholamines and glucagon, thereby promoting adipose tissue lipolysis [52] and a shift in metabolism from fat storage to fatty acid release and oxidation [1]. In support of this, Volek et al [22] reported that serum insulin levels were inversely related to loss of body fat in a 6 week carbohydrate restricted diet trial, and approximately 70% of the variability in fat loss was accounted for by lower serum insulin levels.

Theoretically, carbohydrate driven de novo synthesis of fatty acids in the liver should be reduced by carbohydrate restriction, thereby resulting in reduced hepatic formation of TAG and very low density lipoproteins, with ensuing reduced uptake and esterification in adipose tissue [53]. Also, decreased glucose driven formation of glycerol-3-phosphate in the fat cell should reduce adipose tissue TAG production and storage [15]. Our findings seem to support this line of reasoning since there was a significant loss of adipose tissue mass in subjects ingesting the low carbohydrate diet.

In the Lc+ Ex group no increase in mean LBM could be detected in spite of the 10 weeks of resistance training. On the other hand, there was no loss of LBM in our study, unlike results from earlier weight loss studies [14]. Although low carbohydrate diets seem to reduce the amount of LBM lost with weight reduction [54], some reduction of LBM is still expected [9, 34–37, 47, 55]. Maintenance of, or increase in LBM with resistance exercise has previously been demonstrated in females on calorie restricted diets [26, 27, 56, 57]. The maintenance of LBM in the present trial may therefore presumably be attributed to the resistance training.

The mechanisms behind a lower increase in LBM when on a low carbohydrate diet compared to a diet higher in carbohydrate may in part be explained by a lower energy intake and lower insulin levels. In the Ex group in the present study, there was a significant positive correlation between carbohydrate intake and the increase in LBM. Unfortunately, we do not have data on insulin. Conceivably, a higher carbohydrate intake should give higher insulin levels and thereby stimulate anabolic processes like formation of glycogen, triacylglycerols and proteins [58] and reduce catabolic ones, e.g. lipolysis in fat tissue.

A second explanation for the lack of increased LBM in the Lc+Ex group may be the use of skeletal muscle protein for fuel. Dietary induced ketosis increases the use of amino acids for glucose production [59]. Although no correlation between protein intake and LBM change was found in our study, an association between low protein intake and lean body mass loss has been found in both low carbohydrate diets [14] as well as low calorie diets [18].

Fleck and Kraemer have summarized the findings of 29 studies measuring changes in lean body mass from resistance exercise in untrained individuals [60]. Average increase in LBM constituted 2 kg in 14 weeks, or 0.06 kg of LBM per exercise session. In the studies using only female participants the equivalent number was 0.04 kg LBM increase per session. Our Ex group experienced an average LBM increase of 1.55 kg in 10 weeks or 0.08 kg per exercise session, which is in accordance with, although somewhat higher, than previously reported.

Exercise is in itself a valuable addition to weight loss diets. Meckling and Sherfey showed an added effect of exercise in inducing weight loss with both a low carbohydrate and a high carbohydrate diet. Best results on weight loss were achieved using a combination of exercise and a high protein, low carbohydrate diet [61], thus confirming the findings of Layman et al [62] who also showed that a diet with higher protein and reduced carbohydrate content combined with exercise additively improved body composition during weight loss. On the basis of these studies it seems that carbohydrate restriction in combination with exercise and resistance exercise in particular, offers an advantage over both low fat diets with exercise and low carbohydrate diets without exercise, in improving body composition.

Although there were large individual differences in body composition changes in our study, several subjects experienced very large changes in body composition in a short time period. If the details surrounding the individual differences in response to a combination of carbohydrate restriction and resistance exercise can be more clearly understood, this strategy may prove to be of great importance in the management of overweight and obesity. Also, a change in body composition may be more favorable than weight loss. Resistance exercise is in itself effective for improving body composition and is thus of importance for the treatment of obesity and its related metabolic disorders. It is, however, difficult to quantify the need for muscle mass retention. A small decrease in total muscle mass may not necessarily be considered negative. Obese individuals often have a larger total LBM than leaner counterparts. Loss of body weight will also reduce the load on the musculoskeletal system. With regard to muscle functionality and metabolic role, the quality of muscles may be considered more important than size.

Performance

The attendance at the exercise sessions did not differ between the two groups. In addition the instructors did not observe any group differences in exercise intensity or the ability to perform at the requested loads. We therefore find it less likely that differences in exercise intensity would account for the between group differences in LBM change.

Low carbohydrate diets may result in decreased anaerobic performance [39, 63], but several studies have observed no decrements in aerobic exercise with carbohydrate restricted diets [64]. Indeed, sustained aerobic performance might be beneficially influenced by a high fat diet [65–67]. White et al found a positive correlation between rating of perceived exertion and blood ketones [68]. In contrast, Brinkworth et al [37] recently observed no correlation between blood ketones and ratings of perceived exertion in their 8 week study, and observed no detrimental effects on maximal or submaximal markers of aerobic exercise or muscle strength, compared to an isocaloric high carbohydrate diet.

Unfortunately, performance ability was not measured objectively in the present study, and the possibility of reduced performance with carbohydrate restriction cannot be excluded.

Blood lipids and glucose

As there were no significant effects on fasting serum lipids in subjects performing resistance exercise while on a ketogenic diet, and since carbohydrate restriction generally seem to improve the fasting lipid profiles [5], we would not expect harmful long term effects of the current regime on the fasting concentration of the measured blood lipids. It should be kept in mind, however, that the 24 hour serum lipid load may increase in subjects ingesting a high fat diet in spite of lower fasting levels, since the fasting concentration of TAG is the lowest value during the day on a high fat diet, while it is the highest one on high carbohydrate diet [69]. On the other hand, carbohydrate restriction may lower both fasting and non-fasting serum triglycerides [70] and studies of postprandial lipemia have shown a strong correlation between postprandial triglyceride levels and the level of fasting triglycerides [71]. Additionally, it is well known that the concentration of plasma free fatty acids (FFA) increases on a ketogenic diet [72], and high FFA levels may be an important cardiovascular risk factor [73], especially if sustained. However, plasma FFA levels were not determined in the present trial. In any instance, we consider the exercise part of the present trial to have positive health effects. Both resistance exercise [25] and aerobic exercise [74] have been associated with improvements in CVD risk factors. Previous studies of resistance exercise have demonstrated positive effects on blood lipids [25] which may in part be explained by improved insulin sensitivity, and an increase in skeletal muscle lipoprotein lipase activity, resulting in increased VLDL-triacylglycerol catabolism [75].

Limitations

This is a small study in which only some variables were determined. Habitual dietary intake was not assessed. To be more complete the study should have included determination of insulin levels and sensitivity, as well as albumin bound fatty acids, plasma lipoprotein distribution and fatty acid distribution. In addition, only fasting values of blood variables were determined and the effect of our trial on many CVD risk factors is thus unknown. We also did not account for or make any evaluation of sex or thyroid hormones, catecholamines, glucagon, corticosteroids, all of which known to be metabolic regulators [76–79]. Menstrual cycle phase is known to influence serum lipoproteins [80]. Menstrual cycle was not coordinated with blood collection.