Do BCAAs Break a Fast? The Truth About Amino Acids

James Cunningham, BSc, CPT
Published by James Cunningham, BSc, CPT | Staff Writer & Senior Coach
Last updated: June 20, 2024
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BCAAs (Branched-Chain Amino Acids) can break a fast because of their calorie content, albeit minimal, triggering an insulin response and affecting the fasting state.

As a fitness trainer, clients often ask whether I suggest incorporating BCAAs into their eating window to avoid interference with the fasting process. This prompted me to delve into comprehensive research.

Keep reading to understand how consuming BCAAs during intermittent fasting affects the process and to comprehend their impact on metabolism.

Quick Summary

  •  BCAAs break a fast due to their caloric content, contributing to protein building, even in minimal amounts.
  • BCAAs have been observed to alleviate both physical and mental fatigue following intermittent fasting.
  • Consuming a full dose of the BCAA supplement may be able to provide you with around 20 calories.
  • In my opinion, taking premium BCAA supplements together with a nutrient-dense diet and adequate rest may help you have the energy to support your fitness journey.

Do BCAAs Break A Fast?

holding BCAA Scoop

Yes, BCAAs break a fast due to their caloric content, as one gram of BCAAs provides about five calories, which technically interrupts the fast.

While this is minimal compared to some pre-workout supplements, BCAAs, being amino acids, contribute to protein building, constituting a macronutrient, regardless of their form.

One gram of BCAAs is roughly five calories, technically interrupting the fast. Despite this, the potential benefits of taking BCAAs during a fast may outweigh the drawbacks.


What Does It Mean To Break A Fast?

Breaking a fast simply means ending the period of abstaining from food, typically by consuming a meal or snack.

Some people do this for religious reasons, while others are interested in the potential health benefits.

If you are breaking a fast, it means that you are ending the period of abstaining from food. If you eat, then you’re not fasting.

There are a few exceptions that don’t end the fast. For example, water or tea is ordinarily okay to drink while on a fast.

What Are The Benefits of BCAAs?

plate weighing scale

BCAAs provide benefits like muscle growth, reduced soreness, lower fatigue, and potential blood sugar improvements for those aiming to enhance their training.

While a balanced diet usually meets BCAA needs, supplementation is sometimes necessary. Combining BCAAs with whey protein provides an optimal boost.

Research from the University of Rochester Medical Center suggests that leucine, found in BCAA supplements, is crucial for muscle protein synthesis, preventing protein breakdown, and supporting muscle building [1].

Here are the most common benefits of these amino acids:

  • Increase muscle mass: Many individuals use BCAAs for muscle building, and research from the National Institute of Health strongly suggests their effectiveness in promoting increased muscle tissue [2].
  • Decreases muscle soreness: Engaging in intense resistance training often leads to muscle soreness. BCAAs can assist in alleviating soreness and may contribute to mitigating muscle damage.
  • Reduce physical and mental fatigue: BCAA supplements not only aid in reducing physical fatigue but also help maintain mental alertness. This enables longer workout sessions, contributing to enhanced muscle growth.
  • May lower blood sugar levels: BCAAs can impact insulin levels, with studies indicating an insulin response that prompts muscles to absorb more sugar and lowers blood glucose levels.

It's important to note that individual differences, including age, gender, and fitness levels, can influence the effectiveness of BCAAs. This underscores the need for personalized approaches guided by experts.

What Are The Benefits of Fasting?

alarm clock and plate

Fasting offers various benefits, including improved insulin resistance, weight loss, reduced inflammation, potential heart health improvements, enhanced brain function, and a potential increase in lifespan.

  1. Reduces insulin resistance: Fasting leads to a drop in insulin levels, which can lead to an increase in fat burning, as per the National Institutes of Health [3].
  2. Aids in weight and fat loss: It decreases muscle glycogen, used for energy, leading to water weight loss. Plus, fasting can increase metabolism, speeding up fat loss [4].
  3. Fights inflammation: Research from the Mayo Clinic indicates that fasting can reduce inflammation, potentially preventing diseases like heart disease or arthritis [5].
  4. May improve heart health: Studies show fasting can lower blood pressure and cholesterol, benefiting heart health [6].
  5. Boosts brain function: While mostly studied in animals, fasting might promote nerve cell growth, enhancing brain function. More human research is needed [7].
  6. Could extend lifespan: Animal studies hint at fasting prolonging life and slowing aging, but it's not a surefire way to longevity [8].

How Does Fasting Work?

fruit juice

Fasting works by restricting food intake, often involving abstaining from food entirely and consuming only water or, alternatively, opting for variations such as vegetable or fruit juice fasting.

There is also “partial fasting”, which involves removing certain foods from your diets like processed foods or caffeine.

Intermittent fasting offers a variety of popular methods, such as the 16/8 method, Eat-stop-eat, the Warrior diet, the 5:2 diet, Alternate-day fasting, and spontaneous meal skipping, catering to different preferences and lifestyles.

  1. The 16/8 method
    Fast for 16 hours and eat during an 8-hour window. Adjust the fasting duration based on your comfort—14-15 hours for women.
  2. Eat-stop-eat
    Incorporate a 24-hour fast once or twice a week, avoiding overeating when breaking the fast.
  3. The warrior diet
    Consume small amounts of fruits and vegetables, followed by a 4-hour eating window, typically around dinnertime.
  4. The 5:2 diet
    Eat normally for five days and restrict calories (500 for men, 600 for women) on two non-consecutive days.
  5. Alternate-day
    Fast for 24 hours or consume only a few hundred calories every other day.
  6. Spontaneous meal skipping
    Occasionally skip meals based on your schedule or appetite, ensuring nutritional needs are met in the remaining meals.

"The key with fasting is to stick to a regular structure. I have seen individuals erratically fast based on their schedule and then get frustrated when they don’t feel or see the benefits. If fasting is a tool someone is going to utilize, life has to fall in line with it, and if it doesn’t, that might be a sign you need to rethink it."
- Sydney Greene, MS, RD


man holding tumbler

Do BCAAs Trigger An Insulin Spike?

BCAAs can elevate insulin levels, but it's not a spike. While there's concern for weight loss, BCAAs promote fat loss by reducing insulin. However, the increase from BCAAs isn't significant enough to hinder fat burning, so they don't cancel each other out.

Can You Build Muscle While Fasting?

You can build muscle while fasting, but it will be challenging due to reduced calorie intake and potential difficulty getting enough protein. Intermittent fasting isn't ideal for bodybuilding. It's better suited for weight loss or maintenance.

Will I Lose Muscle If I Fast?

You won't lose muscle if you fast. One study found that weight training during fasting helps preserve muscle. Lack of exercise may impact body composition, but fasting alone does not lead to muscle loss when combined with proper training.


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About The Author

James Cunningham, BSc, CPT
Staff Writer & Senior Coach
James Cunningham, BSc, CPT holds a BSc degree in Sport & Exercise Science from University of Hertfordshire. He's a Health & Performance Coach from London that brings a unique blend of academic knowledge of health supplements and practical exercise experience to the table for his readers.
Learn more about our editorial policy
Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
Learn more about our editorial policy
Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
Learn more about our editorial policy

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