When considering whether a food, beverage, or supplement might break a fast, it’s important to first consider what your goals are around fasting. The three most common reasons people fast are for weight loss/metabolic health, gut rest, or longevity. Let’s look at a few items through that lens.

Coffee

Coffee has minimal calories, but what if we don’t drink it black? We’ll take a look at a few popular coffee picks:

Black Coffee

There have been several studies on intermittent fasting where black coffee was allowed within the fasting window and some studies which allowed consumption of any food or beverage within the fasting window, as long as it was less than 25% of energy needs. With those guidelines in place, fasting was still shown to be associated with benefits around health and prevention of disease. In one literature review, coffee was shown to decrease insulin sensitivity. However, similar to the effects of fasting regimens, reduction in insulin sensitivity was observed in a short-term time frame so further studies are required for longer-term impact assessment. During nutrient deprivation, the cells become slightly more insulin resistant likely due to the body prioritizing fuel to go to the brain instead of other cells in the body. However, when looking at the long-term consumption of coffee, regular consumption has been linked with various positive health benefits including reducing the risk of type 2 diabetes.

Even though black coffee contains minimal to no calories, it does promote functions of digestion. Coffee stimulates gastrin (a hormone that stimulates the secretion of gastric acid), gastric acid secretion, and gallbladder contraction, all of which have an impact on our gastrointestinal tract. Coffee intake may also elicit a reflux sensation, which isn’t ideal for those with heartburn issues.

In addition to the metabolic benefits from coffee, one study showed that the consumption of both caffeinated and decaffeinated coffee trigger autophagy in mice. The authors of this study related the increase in mTOR inhibition and other cellular processes to the polyphenols contained in coffee. However, keep in mind this benefit was seen in animals and has not yet been studied in humans.

The Verdict:

Fasting for metabolic health/weight loss: likely does not break a fast

Fasting for gut rest: does break a fast

Fasting for longevity: likely does not break a fast

Bulletproof Coffee

While black coffee is likely fine to drink in most cases during a fast, bulletproof coffees typically have added butter and medium chain triglyceride (MCT) oil. MCT oil, even though calorically dense, has been demonstrated to improve insulin-mediated glucose metabolism and change fasting serum insulin levels. Plus, MCTs are easily converted into ketones by the body and used as energy. In addition to that, MCT oil has been successfully used to induce ketosis in the management of epilepsy, showing that the consumption of MCT oil can still produce a ketogenic environment.

Butter and coconut oil are both fats, but MCTs are produced from coconut oil, it is 100% MCT composition and butter is mostly long chain triglycerides (LCTs), they have a different effect on our gastrointestinal system. MCTs are absorbed directly through the portal vein and taken immediately to the liver, whereas LCTs stimulate pancreatic enzymes and require bile to be released into the gastrointestinal tract. So, with LCTs, the gut is stimulated and digestive processes occur.

Butter is mostly fat with a small portion of protein. Typically, protein inhibits autophagy, however butter contains such a small amount it’s unlikely that it has an effect. MCT oil contains no protein and is only fat. Energy restriction is also important for autophagy. MCT oil and butter are high calorie foods, so overconsumption of these two items may not provide the low nutrient environment necessary for these longevity benefits. For example, a typical bulletproof coffee calls for 2 Tbsp. butter and 1 Tbsp. MCT oil, which provides ~320 kcal. Therefore, it’s possible that this amount of energy intake either slows or stops these desired benefits of fasting.

The Verdict:

Fasting for metabolic health/weight loss: likely does not break a fast

Fasting for gut rest: though MCT oil has minimal impact on the digestion, coffee and butter break a fast focused on gut rest

focused on gut rest Fasting for longevity: likely breaks a fast

Coffee + Cream

Plain, high-quality dairy by itself likely does not contribute to weight gain or increased risk of metabolic disease. One study was even able to show an association between consumption of trans-palmitoleate (a fat found in milk) and lower fasting insulin levels. However, quantity is key since a couple Tbsp. of cream/milk in coffee is very different than a few cups.

Cream, milk, and other dairy products contain carbohydrates, protein, and fat that do require digestion, so the gut is activated after consumption. Research is limited on dairy and its role in autophagy, but a few studies have shown that high-quality dairy consumption does not increase risk of chronic disease.

The Verdict:

Fasting for metabolic health/weight loss: likely does not break a fast in small quantities

in small quantities Fasting for gut rest: breaks a fast

Fasting for longevity: likely does not break a fast, but research is limited in this area







Tea

A limited number of epidemiological studies have been conducted to determine the association between tea drinking and BMI, but methods for evaluating tea intake as well as numerous confounding variables make tea consumption and weight loss claims relatively weak. Rather, studies evaluate benefits associated with mega doses of the polyphenols found in tea. That being said, plain tea has nearly zero calories per cup, so it likely won’t interfere with ketogenesis and the metabolic benefits people seek from fasting.

On average, tea contains about 2 kcal per 8 fl. oz. cup and about 0.4 gm carbohydrates. Consuming tea in small quantities likely does not provide enough energy to have a big impact on digestion. However, there are many different varieties of teas, containing different ingredients and different quantities of caffeine. Some teas such as peppermint or ginger have been traditionally used to sooth digestive issues, but whether or not tea consumption leads to increased GERD (gastroesophageal reflux disease) symptoms is still up for debate. One meta-analysis concluded that there was no significant relationship between tea consumption and the risk of GERD. However, certain subgroups, such as those from Eastern Asian or Middle Asian descent, may be at higher risk.

There have been a few studies looking at specific properties of tea and its potential to trigger autophagy. These studies have pointed us in the direction of tea’s polyphenols, isoflavones, and other components involved in various mechanisms of autophagy, however, these were all done at the cellular level. Research in humans using realistic doses of tea are very limited. Even though we can’t draw conclusive evidence from these studies, at least we can make an educated guess that tea does not inhibit autophagy.

The Verdict:

Fasting for metabolic health/weight loss: likely does not break a fast as long as sugar isn’t added

as long as sugar isn’t added Fasting for gut rest: dependent upon your personal response to tea and the type/quantity you consume

Fasting for longevity: likely does not break a fast

Lemon Juice

One ounce of pure lemon juice only contains 7 kcal and about 2 grams of carbohydrates. Taking the aforementioned 25% of caloric needs as a fasting protocol framework, ingestion of a 3 ounce serving of pure lemon juice, contributing 6 grams of carbohydrates, is not enough to disqualify you from being in a fasted state nor is it enough to push someone out of ketosis.

Lemon juice does contain calories and carbohydrates which will need to be digested, so the gut will be stimulated. The carbohydrates in lemon juice are a mix of sucrose, fructose, and glucose, all of which need to be metabolized by the gut and liver.

Some research suggests that over consumption of fructose can lead to health issues such as NAFLD and obesity. However, others argue that the source of fructose may be more important, stating that high intake of fruits with high fructose content can be associated with good metabolic health. Since lemon juice is only 20% fructose per carbohydrate gram and since we generally do not consume large quantities of lemon juice, it likely does not have a significant impact on longevity and long-term health.

The Verdict:

Fasting for metabolic health/weight loss: likely does not break a fast if consuming less than 3 fl. oz.

if consuming less than 3 fl. oz. Fasting for gut rest: breaks a fast

Fasting for longevity: likely does not break a fast

Bone Broth

Bone broth does contain protein, a small amount of carbohydrates, and sometimes fat. Carbohydrates and protein can kick someone out of ketosis if consumed at high enough quantities. Those specific quantities vary from person to person, but in general, more than 50 grams of carbohydrates and more than 80 grams of protein can be sufficient to completely prevent ketone production. The nutritional content of bone broth varies greatly based on the method of cooking, duration of cooking, and ingredients used—that said, on average, one cup of bone broth ranges from 31 to 86 kcal, 0.2 to 2.9 grams of fat, and 4.7 to 6 grams of protein. These amounts are unlikely to completely kick someone out of ketosis, but may slightly slow down the breakdown of fat.

Though bone broth is sometimes used for gut health, it typically contains carbohydrates, protein, and fats; all of which need to be digested and stimulate the gut.

In one animal study, they saw an inhibition in autophagy when supplemented with glycine (one of the main amino acids in bone broth). However, it is questionable whether this translates to humans. When looking at other aspects of health, bone broth contains essential nutrients such as calcium, magnesium, potassium, and collagen, so it is a nutrient-dense product that can be useful for optimizing nutritional intake. For overall health impact, bone broth is a positive choice, but for promoting autophagy more research is needed.

The Verdict:

Fasting for metabolic health/weight loss: likely okay to consume in small quantities , but you may not see as significant results with fat loss and metabolic health

, but you may not see as significant results with fat loss and metabolic health Fasting for gut rest: breaks a fast

Fasting for longevity: more research is needed, so likely best to avoid if fasting for this reason

Gum

The type of gum has an impact on whether or not it breaks a fast. Original gum contains sugar, which we consume when chewing it. If you’re having multiple pieces per day, the calories and grams of sugar can definitely add up. For example, Original Bubble Yum has 25 kcal, 6 grams of carbohydrates, and 5 grams of sugar per piece. If you were to have 4 pieces in one day, you’d be getting 100 kcal and 20 grams of sugar. This will likely have an impact on ketogenesis and your ability to optimally burn fat. Sugar-free gums made with sugar alcohols will still provide a small amount of calories. For example, Spry gum has 1.7 kcal and 0.72 g of carbohydrates per piece. In very large doses, some studies have shown xylitol to cause a small increase in glucose and insulin levels. However, the quantity used was equivalent to over 40 pieces of gum, which is an unrealistic amount to consume in one day.

Regular sugar gum will require digestion and metabolism. Sugar-free gum is debatable. Our bodies are unable to completely digest and absorb 100% of sugar alcohols, though all are partially absorbed to some degree, which triggers our gut.

Sugar consumption in excess is related to poor health and higher risk of chronic disease. So, consuming sugary gum, especially when trying to fast for these benefits, isn’t a good idea. Sure, 5 grams of sugar a couple times a month probably won’t have a long-term impact, but if you’re consuming this daily while intermittent fasting, or it starts to trigger a sugar craving, then having this gum could be causing more harm than good. For sugar-free gum, research is limited on its effects on longevity and autophagy. From the limited research that exists, they are probably safe to consume. Sugar-free gum, ingested in non-excessive amounts, would not impact an individual’s energy-deficient state nor would it account for amino acid uptake. It is therefore reasonable to assume that there would be minimal impact on the regulation of autophagy.

The Verdict:

Fasting for metabolic health/weight loss: regular gum breaks the fast, sugar-free gum does not

Fasting for gut rest: breaks a fast

Fasting for longevity: regular gum breaks the fast, sugar-free gum likely does not

Apple Cider Vinegar

A tablespoon of apple cider vinegar (ACV) has 3 kcals and 0.1 grams of carbohydrates—in essence, very little nutrients. This small amount likely does not inhibit ketosis or the ability to break down fat.

Apple cider vinegar promotes stomach acid production, so it does stimulate the gut.

Apple cider vinegar does not contain protein and contains minimal calories, so nutrient sensing pathways involved in autophagy are likely not triggered with its consumption. The benefits of ACV are mostly seen with improving stomach acid/reflux issues and its connection to greater health and longevity benefits is still up for debate.

The Verdict: