What Breaks a Fast and What Doesn’t? Your Guide

If you’ve ever experimented with intermittent fasting, you’re probably familiar with the experience of asking the internet some version of: is (insert food or drink here) going to break my fast? 

And you’ve probably noticed that in many cases there’s no definitive answer. Why? The way I think of it, it’s because fasting isn’t binary. It’s more like a spectrum. Fasting creates several different health effects, and a small amount of calories or different kinds of nutrients may change some of them but not others. 

There’s also general disagreement around which foods and drinks do affect your fast in any way. And there’s the consideration of bioindividuality: how my body responds to a spoonful of MCT oil in coffee may be different from how yours does (don’t worry, I’ll address both coffee and MCT oil below). 

With all of these considerations in mind, I hope this article will bring you some clarity and understanding of the nuances so that you can make the best decisions for your own fasting journey. 

What Does It Mean To Break Your Fast? 

The really short version is that anything with calories breaks a fast—technically. But when my functional medicine telehealth patients ask me about what they can or can’t eat or drink, I also like to consider context, including the person’s individual goals. 

Consuming a few calories might break your fast, but is it meaningfully impacting the key pathways we associate with the health benefits of fasting, like insulin signaling, digestion, mTOR (the growth pathway activated by protein), or autophagy and cellular cleanup? It depends on the food, its macronutrient breakdown, the quantity, the type of fast or fasting period, and your bioindividuality. 

The Fasting Spectrum

With all of that context in mind, we can really think of a fasting spectrum from completely pure to more flexible. 

A key example of this concept is the fasting mimicking diet, which is a carefully designed eating plan developed by researcher Valter Longo that’s low in overall calories, protein, and carbohydrates, and higher in healthy fats. While you’re eating actual food here, research shows that this eating plan mimics many of the effects of a true water fast. (1) 

While we don’t always have thorough research on every possible food or drink and whether or not it breaks a fast, we can use that concept and what we know about the impact of different kinds of macronutrients to help guide our fasting decisions. 

The Strict or Pure Fast 

If you want to stay on the safest side of maximum possible fasting benefits, consume nothing but water. This is the only surefire way to make sure that you’re absolutely not breaking your fast or interfering with any of the pathways of fasting. 

And while we’re here, not only can you drink water on a fast, you need to drink water, and lots of it. Water is important all the time, but especially during a fast when you are not consuming fresh foods that contain water and help keep you hydrated. Water is even more important in the summer months and if you exercise frequently. I recommend keeping your water intake around 64 ounces daily and sipping on it regularly during your fast.  

Does Coffee Break a Fast? 

This is probably the most common question I’m asked when it comes to intermittent fasting, and I understand why. 

And I’m always happy to provide the good news for coffee lovers, which is that black coffee is very unlikely to break a fast. (2) 

Coffee on its own contains negligible calories and no sugar, and it can actually provide additional benefits including supporting metabolic health and flexibility and increasing fat burning. Coffee may also improve satiety and make fasting easier. 

In some fasting circles, I’ve heard it discussed that caffeine shouldn’t be consumed during a fast because it can raise cortisol levels, which could disrupt some of the benefits of fasting by stimulating your stress response. (3) 

This is another area where bioindividuality matters. If you’re drinking enough coffee that you’re feeling jittery and anxious, or if you are very caffeine sensitive, then you may want to avoid it or cut back while fasting. You don’t want to be in an overtly stressed out state. 

But I also don’t think we have to get too hung up on a mild and temporary increase in cortisol. Fasting itself is a hormetic (positive) stress, and a brief cortisol rise isn’t inherently bad. (4) 

So in my opinion, as long as you’re not sensitive to caffeine or overdoing it, it’s fine to keep drinking your coffee. What you don’t want to do is add sugar or dairy creamers (which do break your fast). 

Does Tea Break a Fast? 

As with coffee, black, unsweetened tea, whether caffeinated or not, is unlikely to break a fast. I love sipping on Earl Grey when I’m fasting, as well as different kinds of herbal teas which each have their own additional health benefits. 

Again, the important caveat is that you don’t want to add anything to your tea that would break your fast. 

Get my free Tea Guide here: Tea Guide – Dr. Will Cole 

Do MCT Oil, Coconut Oil, and Other Fats Break a Fast? 

Adding pure, healthy fats like MCT oil, coconut oil, or ghee to your coffee or other beverages will add calories, which technically breaks a fast. However, small amounts of pure fats don’t significantly raise insulin levels because there’s no protein or carbohydrate content. So in small amounts, this will usually keep you in something similar to the fasting-mimicking state. 

For some people, adding a small amount of these fats helps them extend their fasting windows without stress, so in these cases, I think it’s a great idea. Of course, keep in mind that the more you consume, the higher number of calories you’re taking in, so you might start to see fasting benefits decrease. I would usually suggest sticking to one serving—for example, adding a spoonful of MCT oil to one cup of black coffee in the morning while fasting. 

Do Collagen or Almond Creamers Break a Fast? 

There’s a key distinction between adding a spoonful of MCT oil to your coffee and adding a spoonful of collagen to your coffee, which is that one is fat and the other is protein. Maybe that sounds obvious, but many people don’t realize that it’s not just calories that matter when it comes to what breaks a fast, it’s the macronutrient breakdown. 

Collagen protein powders or creamers and almond milk contain some calories and can activate digestion and mTOR, if minimally. Looking again at the fasting mimicking diet, we know that people can still experience many fasting benefits even with some (minimal) protein intake. 

Personally, I usually avoid collagen and other proteins until the end of my fast because mTOR is particularly sensitive to protein, and activating it shifts cells away from autophagy. But again, this is really an individual choice. 

If you do include an almond, collagen, coconut, or other creamer, make sure to check the ingredients to ensure there’s no added sugar or artificial sweeteners. 

Does Bone Broth Break a Fast? 

Bone broth, which I absolutely love and recommend to just about all of my patients, falls into the same general category as collagen and almond milk. It contains collagen itself (this is one of the primary reasons it benefits your health) and the protein content makes it more likely to activate mTOR, even if calories are low. 

However, you can again likely achieve many fasting-like benefits while drinking bone broth, and if you’re in need of more nourishment, this is a great option to include. 

How to Break a Fast Gently

When you’re ready to intentionally break your fast, I recommend opting for gentle, easy to digest, nutrient-dense foods including bone broth, soups or stews, avocado, or steamed vegetables. Avoid large, heavy meals, and of course, as always, avoid processed foods, excess sugar, and refined carbohydrates. 

Personalizing Your Fast

As I write about in Intuitive Fasting, fasting isn’t one-size-fits-all, and there are many ways to customize your routine and introduce flexibility into the process. When it comes down to what breaks a fast specifically, one tool that can be helpful is using a continuous glucose monitor (CGM) or another wearable health tech device that helps you understand how what you eat and drink (or don’t) actually affects your blood sugar levels and other metrics. Over time this can also help you tune in more intuitively to your body without having to rely on data all the time. 

The Takeaway

When it comes to fasting, I don’t think we always need to be aiming for perfection. If a little bit of coconut oil or collagen helps you fast longer, feel better, and stay consistent, you’re probably still getting most of the benefits of being in a fasted state. Ultimately, the best fast is the one your body responds well to, and that you can sustain. 

As one of the first functional medicine telehealth clinics in the world, we provide webcam health consultations for people around the globe. 

Sources

• Wei, M., Brandhorst, S., Shelehchi, M., Mirzaei, H., Cheng, C. W., Budniak, J., … & Longo, V. D. (2017). Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science translational medicine, 9(377), eaai8700. 
• Sciarrillo, C. M., Keirns, B. H., Elliott, D. C., & Emerson, S. R. (2021). The effect of black coffee on fasting metabolic markers and an abbreviated fat tolerance test. Clinical Nutrition ESPEN, 41, 439-442.
• Lovallo, W. R., Whitsett, T. L., al’Absi, M., Sung, B. H., Vincent, A. S., & Wilson, M. F. (2005). Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Biopsychosocial Science and Medicine, 67(5), 734-739.
• Mattson, M. P. (2008). Dietary factors, hormesis and health. Ageing research reviews, 7(1), 43-48.