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What Breaks A Fast? How Many Calories Can Break A Fast

Christine VanDoren

Updated on - Written by
Medically reviewed by Kathy Shattler, MS, RDN

how many calories break a fast

Fasting has become a popular approach for helping kickstart your body’s ability to burn fat, stabilize blood sugar levels and balance cholesterol levels, something scientists have been tracking[1] since the 1930s with experiments that showed calorie-restricted diets prolonged the lives of lab rats. Recent studies of intermittent fasting and its benefits[2] have found that a modified fasting diet that includes fasting every other day for eight to 12 weeks helps reduce blood lipids by up to 50% and helps control blood pressure and blood sugar. 

Researchers assert that intermittent fasting plans intended for weight loss, such as fasting periods lasting between 16 and 20 hours a day, can result in “greater fat metabolism and reduced fat storage[3]”. These are encouraging findings for the health community when it comes to using intermittent fasting to control fat, body weight, and overall health.

In programs where periods of caloric restriction are alternated with periods of caloric intake — the true nature of intermittent fasting — the eating period that follows a fasting period is referred to as “breaking” the fast. This is also where the word “breakfast” originates; it’s the first meal that breaks the fast that happens while you sleep. 

If you’re using a fasting program to lose body fat or improve your health in general, knowing the specifics of how a fast is broken can help ensure success from your specific regimen.

How Many Calories Breaks A Fast?

Expert opinions vary on the number of calories it takes to truly break a fast, with some stating that eating fewer than 50 calories[4]  breaks your fast and others saying staying as close to 50 grams of carbohydrates[5] as possible will keep your body in a state of ketosis, or burning stored fat, which is the objective of the fasting period for most people. However, many people also fast for the purpose of cleansing and purifying their bodies. For anyone who falls into this group, the consumption of any calories whatsoever breaks the fast.

The overriding logic asserts that you should stay as close to zero calories as possible to keep from negating the benefits of your fast, which is what anyone participating in a fasting program would anticipate. Given these guidelines, eating anything more than zero calories[6] can be considered breaking your fast, though it’s equally important to have a proper eating plan full of healthy foods before you reach your next eating window to avoid taking in too many calories and eating foods that might derail your progress. 

Once you move from fasting to eating, especially at the beginning of your fasting program, it can be tempting to eat whatever might be available when you’re finally able to eat again. Having a solid eating plan each day and making sure you have healthful options available and ready can help prevent you from eating out of hunger rather than eating to achieve your health goals.

What Breaks a Fast?

In general, eating food is considered the breaking of a fast, though opinions vary among nutritional experts on the number of calories needed for a fast to be broken. A strict fasting program sticks with the zero-calorie rule, which means taking in any new calories is the point at which the fast is broken. 

If your goal is fat loss, it’s essential to give the program its best chance to work, which may mean following a strict program and breaking your fast only during your eating window when you can consume more than the 50 calories that will keep you in your fasting state as described above.

When your body is in ketosis during a fast, it’s converting the fat stored in your body into fuel, which is the fat-burning state you’re hoping to achieve with your fasting program. Once you begin consuming calories and carbohydrates again, ketosis is halted, and your body switches to using glucose for fuel. Your glucose stores are replenished by the food you eat, and this is a process that can cause your body to store fat in reserve if your program isn’t conducted properly. 

An easy way to think about how to approach your program in which breaking your fast is concerned: By considering “fasting” to mean “no calories” and “eating” to mean “consuming calories,” you can think of your first meal after your fasting window with its total calorie and carbohydrate load to be what truly breaks your fast.

What To Eat While Fasting?

Calories taken in during intermittent fasting are meant to be consumed during the eating periods of the program, with alternating periods of food consumption and fasting making the most of your body’s natural mechanisms for burning fat. This means that the true ideal for what you should eat during a fasting period is literally nothing since an actual fast restricts calorie intake to an amount as close to zero as possible. 

There are versions of intermittent fasting[7] (IF) that may use a very-low-calorie diet (i.e., Prolon[8]) or one meal a day during fasting periods rather than avoiding consuming calories altogether. While these programs take a different approach to fasting than the total zero-calorie programs, there are still benefits to be gained from them. In such programs, eating clean foods that include fiber and healthy fats can make you feel full without adding more calories than necessary, allowing you to maintain a minimized eating “fasting” period without compromising your progress. This is not a truly fasted state and may not necessarily reap the benefits of increasing insulin sensitivity and giving your digestive system a rest, depending on the intermittent fasting plan you are on.

If you’re adhering to a strict no-eating fasting program such as the IF 12/12 or 16/8, what you eat and how many calories you consume during your eating window depend on your starting point, overall health, fitness, and weight loss goals. A 12/12 IF plan consists of a 12-hour fasting window and 12 hours of eating, while a 16/8 is 16 hours of fasting and 8 hours of eating. During the fasting window, black coffee, herbal teas, and water may be consumed, while the consumption of diet soda is controversial due to the potential effects of artificial sweeteners on blood sugar and the gut microbiome.

Obvious dietary logic dictates that your choices during the eating window of your fast should be foods low on the glycemic index, fiber-rich, high in protein and healthy fats, and low in added sugars and saturated fats—in other words, a sensible diet. By planning your eating windows to be as healthful as any other diet you would opt for to lose weight and burn body fat, you give your physiological systems their greatest advantage to working in your favor. This increases your chances of finding success in your fasting program!

What To Drink During A Fast?

It’s crucial to stay hydrated during a fast. Hydration is the vehicle for providing oxygen to your cells, which can be neglected when focusing intently on keeping your fasting and eating windows clean and distinct from one another.

Since the goal is to remain as calorie-free as possible during a fast, water, coffee and tea are the best things to drink during your fasting period. All of these will adequately hydrate your cells and provide enough electrolytes to keep your systems a balance between eating periods. Herbal teas help by adding a bit of flavor to satisfy your need for something more robust than plain water, in addition to whatever health benefits the herbs provide.

If water and herbal teas aren’t enough to satisfy your thirst, take a coffee break which can keep you from feeling like you’re missing out during your fasting windows. 

If you’re okay with the under-50 calorie rule, a cup or two of coffee or tea without artificial sweeteners or creamer should keep you within your limits. You should remember to increase your water intake to balance out the diuretic effect of caffeine in both drinks and prevent the possibility of dehydration. 

No matter what you choose to drink during your fast, the most important thing to remember is to drink enough fluids to stay hydrated until your next eating window. This will also keep your stomach full and help with the hunger sensations you might feel until your body fully adjusts to the cycle of your fasting program.

Final Thought

Knowing how to break a fast without upending your progress is as important as knowing when not to eat. The impulse to eat foods that aren’t on your eating plan or to over-consume calories that might be considered healthy can be surprising for those in a fasting program, especially when the program is in its beginning stages. 

Reducing and regulating your body weight through fasting can reap great rewards, even beyond losing unwanted pounds and inches. Understanding how and when to break your fast is key to maximizing the benefits you can expect from your fasting program. It may even help you control some adverse health conditions you have been struggling with.

Anecdotal reports from participants in studies have included energy boosts, increased mental clarity, and improved sleep, among other benefits that can help make a fasting program more desirable as part of your fitness regimen. And since adhering to a strict fasting schedule forces you to be hyper-aware of when, what, and how much you eat, it also helps you constantly gauge your overall eating habits. This hyper-awareness is especially important to be mindful of when it comes time to break your fast. 

As with any significant change in your eating and nutritional practices, you should consult with your doctor and a Registered Dietitian (RD) before starting a fasting program to make sure this regimen is right for you.


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    1. Centre for Healthy Brain Ageing (CHeBA). (2013). Fasting for a Longer Healthy Life: Is There a Scientific Basis? [online] Available at: https://cheba.unsw.edu.au/blog/fasting-longer-healthy-life-there-scientific-basis#:~:text=The%20scientific%20study%20of%20the,producing%20malnutrition%2C%20prolonged%20their%20lifespan.
    2. ‌Wang, Y. and Wu, R. (2022). The Effect of Fasting on Human Metabolism and Psychological Health. Disease Markers, [online] 2022, pp.1–7. doi:10.1155/2022/5653739.
    3. ‌Mandal, S., Simmons, N., Awan, S., Chamari, K. and Ahmed, I. (2022). Intermittent fasting: eating by the clock for health and exercise performance. BMJ Open Sport & Exercise Medicine, [online] 8(1), p.e001206. doi:10.1136/bmjsem-2021-001206.
    4. ‌24 Hour Fast (2020). How many calories break a fast? | 24 Hour Fast. [online] 24 Hour Fast. Available at: https://24hourfast.com/how-many-calories-break-a-fast/ ‌
    5. Kumar, K. (2021). How Many Carbs Will Disrupt Ketosis? Keto Guidelines. [online] MedicineNet. Available at: https://www.medicinenet.com/how_many_carbs_will_disrupt_ketosis/article.htm ‌
    6. Collier, R. (2013). Intermittent fasting: the science of going without. Canadian Medical Association Journal, [online] 185(9), pp.E363–E364. doi:10.1503/cmaj.109-4451.
    7. ‌Hopkinsmedicine.org. (2022). Intermittent Fasting: What is it, and how does it work? [online] Available at: https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
    8. ‌Schilling, R. (2019). Fasting Mimicking Diet For 5 Days Every Month. [online] Medical Articles by Dr. Ray. Available at: https://www.askdrray.com/fasting-mimicking-diet-for-5-days-every-month/ ‌
Christine VanDoren

Medically reviewed by:

Kathy Shattler

Christine is a certified personal trainer and nutritionist with an undergraduate degree from Missouri State University. Her passion is helping others learn how strong and healthy they can become by transforming their daily habits. Christine spends most of her time in the gym, hiking, painting, and learning how she can influence others through positivity!

Medically reviewed by:

Kathy Shattler

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