The Simple Guide to What Breaks A Fast: Food, Beverages, & Supplements

One of the most common questions in the fasting community is: Does X break a fast?

The X can be coffee, branched-chain amino acids, a spoon of MCT oil, or a scoop of protein powder. Coffee is of special interest since billions of people start their day with it. 

Does X break a fast? The answer depends on a few things. It depends on the substance consumed, but it also depends on the fasting regimen and the person pursuing it.  

For instance, some fasting protocols allow limited portions of calories. That opens things up significantly. 

Let’s start by defining fasting, then we’ll apply what we’ve learned to a list of common drinks, supplements, and sweeteners to see if they “break” a fast.

Defining Fasting

Fasting can be defined as a temporary period of macronutrient deprivation. In other words, a fast is a time that you restrict fat, protein, and carbohydrate calories. 

Yet this definition says nothing of how long the fast should be or how aggressively calories should be limited. To sharpen it up, let’s explore the different flavors of fasting. 

First, consider intermittent fasting (IF) vs extended fasting. Intermittent fasting, also called time-restricted feeding, is generally defined as any fast between 12 and 36 hours. When a fast exceeds 36 hours, it’s generally considered an extended fast. 

Within these broad categories are different fasting protocols. For instance, the IF protocol known as OMAD (one meal a day) entails consuming all your daily calories in one sitting. For the remainder of the day you consume zero calories.

On a 5:2 protocol, however, you consume 25% of your normal calories two times per week. This is called a modified fast, and it’s been shown to have benefits—weight loss, insulin sensitivity, and other metabolic improvements—similar to zero-calorie fasts.[*] 

Another brand of modified fasting is the Fasting Mimicking Diet (FMD). Pioneered by longevity researcher Dr. Valter Longo, the FMD entails reducing calories 5 days per month and has been shown to have metabolic benefits in humans.

So the first thing to realize is that not all fasting protocols involve total calorie restriction. Let’s go deeper into what it means to break a fast. 

What Does It Mean To Break a Fast?

What breaks a fast will depend on the specific fasting protocol. The quick and dirty answer, however, is that consuming calories breaks a fast. 

Consuming calories takes your body out of fasting mode and puts it into growth mode. Both are important in order for the human body to flourish. 

In fasting mode, you burn fat, make ketones, and activate a cellular recycling program called autophagy.[*] In growth mode, you store fat, build muscle, and repair tissue. You break it down, then you build it back up again.  

Why does consuming calories put you in growth mode? There are several factors, but perhaps the most important is the hormone insulin.

Insulin is a growth hormone. It helps you build muscle and store energy for later. When you eat a meal—especially a meal with carbohydrates—insulin rises to shut down your fast.[*] 

Another player is called mTOR, a genetic growth pathway activated by the consumption of protein and carbs.[*][*] When mTOR goes up, another pathway called AMPK (linked to the benefits of fasting) goes down.[*] 

And so consuming calories—especially carbohydrate and protein calories—activates the systems that break a fast. As you might imagine, the amount of calories matters. 

A few grains of rice won’t have a meaningful insulin impact, but a few scoops will. Keep that in mind as we review our list of comestibles. 

Does It Break A Fast? (DIBAF)

Review this list and find out. 

Beverages

Coffee

Everyone wants to know if coffee breaks a fast. Some purists are sticklers for water-only fasts, but since coffee is non-caloric, it’s probably fine. Also, coffee has been shown to induce autophagy in mice, so it may actually enhance your fast.[*]  

DIBAF? Unlikely.  

Tea

Similar to coffee, tea contains zero calories and a bunch of antioxidants. Nothing to spike insulin or mTOR. Nothing to break a fast. 

DIBAF? Unlikely.

Bone broth  

Bone broth does provide protein calories, but its constituent amino acids (like glycine) have smaller impacts on growth pathways than amino acids like leucine.[*] A mug or two shouldn’t derail your fast.   

DIBAF? Not meaningfully. 

Diet soda

Is diet soda part of an ancestral diet? No. That said, will the ingredients spike insulin or mTOR? Also no.[*] 

DIBAF? Unlikely.

Water

Water is on this list because some people practice “dry fasting”. But since fasting has a diuretic effect (you lose fluids more rapidly), going dry could be dangerous. Stay hydrated. 

DIBAF? No.

Supplements and Sweeteners

MCT oil, butter, or creamer

Does adding fat to your morning coffee break a fast? Technically yes, but since fat has a minimal insulin impact, it shouldn’t meaningfully interfere.  

DIBAF? Not meaningfully. 

Branched-Chain Amino Acids (BCAAs)

Leucine, isoleucine, and valine are three amino acids (the building blocks of protein) known as BCAAs. These amino acids (especially leucine) stimulate mTOR and activate muscle synthesis.[*] Because of this, they’re best avoided during a fast.  

DIBAF? Yes. 

Protein powder

Same message as the last section. Consuming protein raises mTOR and insulin.

DIBAF? Yes. 

Electrolytes

During a fast, you pee out electrolytes like sodium and potassium at higher rates.[*] Replacing these minerals may help prevent the fatigue, weakness, headaches, and cramps that manifest for similar reasons as Keto flu. Just make sure you choose an electrolyte product with zero sugar. 

DIBAF? No. 

Sweeteners

Non-caloric sweeteners like aspartame, sucralose, allulose, stevia, monk fruit, and erythritol don’t significantly raise insulin levels and therefore shouldn’t interfere with a fast.[*][*][*]  

DIBAF? Unlikely. 

Multivitamins

No two multivitamins are exactly alike, and you’ll need to check the ingredients for anything that could cause an insulin response. Tablet-style multivitamins that contain nothing aside from vitamins and minerals likely won’t break your fast. Multivitamins that come in a gummy or chewable form may contain sugars or proteins, which raise insulin levels and bring you out of your fast. Regardless of the exact ingredients, many people find that multivitamins cause digestive discomfort when taken on an empty stomach. For this reason, you may want to consider waiting until your feeding window to take a multivitamin.

DIBAF? Depends on the exact ingredients. 

Other Supplements

As above, this depends on the exact ingredients. If it contains an insulin-reactive sweetener or more than a handful of calories, it will break a fast. If the only ingredients are vitamins, minerals, or a couple of calories worth of herbs, then it likely won’t break a fast. With that being said, some supplements (particularly those that are fat soluble) are absorbed best with food, so you may want to consider taking them during your feeding window even if they won’t break your fast. 

DIBAF? Depends on the exact ingredients. 

Best Foods to Break a Fast

Not sure what to eat to break a fast? We’ve got you covered. First, don’t overthink it. Despite what you might read in those magazines near the checkout at the supermarket, you’re not required to eat fermented siberian cabbage soup or anything crazy to break your fast. Just use common sense—start with gentle foods, avoid anything too heavy, and resist the urge to overeat. 

Here are a few ideas for gentle foods to break a fast on Keto:

• Smoothies
• Cooked vegetables w/ oil (Avoid raw cruciferous veggies)
• Salad drizzled with EVOO
• Small amounts of poultry and fish
• Nuts & nut butters
• Soups
• Eggs
• Avocados
• Bone broth

Don’t Stress About Fasting

Many of the items that people worry about—coffee, tea, MCT oil, bone broth, stevia, etc.—don’t have the calories or metabolic effects to meaningfully interfere with a fast. 

Besides, fasting isn’t all or nothing. You can still benefit while consuming limited calories. 

So keep the above list in mind, and don’t stress too much about what breaks a fast. You’ll enjoy life more that way. 

Whether you’re a seasoned fasting pro, or curious to try this powerful health and weight-loss tool, Carb Manager’s IF tracker makes it just as easy to manage the time you’re not eating as it is to track daily meals. Premium members can choose from popular programs like 16:8 and OMAD, set custom fasting/eating windows, count down with our fasting timer, and more. 

Please note that as with any significant diet or lifestyle change, we recommend working alongside a registered health professional, especially if you are currently on any prescribed medications or undergoing any medical treatments. Fasting is not appropriate for everyone and should be avoided by those with a history of eating disorders, pregnant and breastfeeding women, and anyone under 18.