What Breaks a Fast? A Full Guide

Those new to intermittent fasting may find themselves questioning what they can (and cannot) consume during their fast, especially when it comes to controversial foods and beverages like zero-calorie foods and certain vitamins. Unfortunately, many individuals only focus on what they can’t have while fasting, but breaking a fast safely and correctly is just as important.

Key takeaways:

What is intermittent fasting?

Intermittent fasting is a diet method that alternates between periods where one restricts from food entirely or consumes very little, resulting in a significant calorie reduction, and periods where you consume your daily calorie allotment. After a few hours of fasting, the body’s glucose supply will diminish, resulting in the need for a new energy source by burning fat.

Researchers have found that intermittent fasting can possibly have benefits including:

  • Weight loss
  • Improved cognition
  • Lowered blood pressure
  • Improved type 2 diabetes

The easiest way to track fasts is to use specialized intermittent fasting apps.

What does it mean to break a fast?

This is where intermittent fasting can become controversial. It’s often said that consuming any amount of calories, no matter how big or small, will disrupt the fasting process. Meanwhile, beverages like black coffee and tea, which only contain about five calories per cup, have been made an exception.

So, how do we know what breaks a fast and what doesn’t?

Technically consuming any amount of calories breaks a fast. However, if your calorie intake is very low and contains minimal carbs, you may remain in ketosis. When in ketosis, you may still experience some fat-boosting and appetite-suppressing benefits.

Melissa Mitri, MS, RD, Nutrition Writer, Owner of Melissa Mitri Nutrition.

Zero-calorie rule and fasting

During your fasting window, you are really not supposed to have anything other than water. However, it may be okay to have a few select beverages during a fast, as long as they are very low in calories. A few examples are unsweetened coffee or tea with a splash of almond milk, coffee blended with a small dose of MCT oil, or bone broth. While these are generally lower calorie options, bone broth, for example, is high in protein and can therefore stop the autophagy progress and break your fast.

Reintroducing foods back into your system

After several hours of fasting, the body continues to burn fat while ketones supply an alternative energy source. It also induces autophagy, a process by which damaged or old cells are destroyed and their constituents are recycled to regenerate new, healthier cells.

When transitioning from a fasting state to an eating window, following a few rules can make the transition much smoother for the body. Here are a few tips to follow as you start your eating window:

  • Introduce small portions to start. Your body has just been through several hours of calorie restriction, and consuming large amounts of food quickly can shock your digestive system, causing stomach upset, bloating, and a spike in insulin levels.
  • Avoid foods high in fats, sugars, and carbohydrates. Breaking your fast with foods high in fat, sugar, and carbohydrates (anything processed) can be difficult to digest and cause many problems, including spiked insulin levels, diarrhea, and bloating, and counteract the benefits of your fasting period.
  • Avoid binge eating when breaking a fast. Binge eating can be common in intermittent fasting due to the fact that it takes approximately 20 minutes for your brain to send a signal to the stomach that it's full, making it more likely to overeat. The Department of Psychological and Brain Sciences at Texas A&M conducted a study on the binge-eating habits of individuals who participated in intermittent fasting. Researchers found that intermittent fasters were less likely to listen to their body's natural hunger and satiety signals and instead focused on the external rules.

What should I eat to break a fast?

When breaking a fast, it’s important to be cautious about what you eat when first breaking a fast and stick to nutrient-dense foods that benefit the body. After fasting for several hours, the body needs to replenish all of the nutrients, therefore, following a fasting period, your diet should include the following:

  • Healthy fats. This can include foods like nuts, seeds, and avocado.
  • Lean protein. Fish, poultry, greek yogurt, and eggs are all excellent choices. Try to avoid other animal proteins like cheese and red meat.
  • Legumes or beans. This includes lentils and a variety of beans such as garbanzo or black beans.
  • Soups. It’s best to avoid heavy soups that are dairy-based and instead opt for lighter soups that are loaded with vegetables. Bone broth is a great option that you can sip on if your body struggles to transition between fasting and eating windows.
  • Smoothies. Smoothies are an excellent way to ease back into the eating window as it’s easily digestible and can be packed with nutrients from fresh fruit and vegetables, yogurt, seeds, and other plant protein options.

What supplements will break a fast?

There are several vitamins and other supplements available. Some have been deemed as fasting-friendly while others should be avoided while fasting.

BCAAs (branched-chain amino acids)

BCAAs are among the most controversial supplements. They are made up of proteins (found in many foods), and protein can stop the fasting benefits; thus, most BCAAs should be avoided. L-tyrosine is one exception, as it contains very few calories and shouldn’t affect the fast, but if you’re trying to achieve autophagy, it is recommended not to take it.

Creatine is another exception, as it doesn’t contain any sugar and is a non-proteinogenic amino acid, so it doesn’t cause an insulin release.


Collagen is a low-calorie supplement with approximately 30 calories per serving. It has too many calories to be considered fasting-friendly. It also contains amino acids, which can kick you out of your fast. It’s best to take supplements like these during your eating window.

Vitamins and minerals with "unnecessary additives"

Most vitamins and minerals are safe to consume while fasting, but it’s important to always check the back of the label for any unnecessary ingredients. This includes added calories, sugar, and artificial sweeteners, which can stop the ketosis and autophagy processes. These ingredients are typically found in gummy vitamins and will break a fast.

It’s always a good idea to check the label of your vitamins and supplements before starting an intermittent fast. If you’re hesitant, you can always take them during your eating window just to be safe. Any medications prescribed by a doctor should be taken as directed, and if you’re new to intermittent fasting, consult with your doctor before starting the program to ensure it’s a safe diet method for you.

While the fasting portion of intermittent fasting can feel like the biggest hurdle, properly breaking a fast carries its own share of difficulties. Making sure you get enough of the right nutrient-dense foods you need while not overeating can be overwhelming at first, but it becomes easier over time. Intermittent fasting has proven its many benefits through research, but taking care of your body between these fasting windows is just as important for a healthy lifestyle.

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