ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, Do BCAAs Break a Fast? And, Does it Matter?


Do BCAAs Break a Fast? And, Does it Matter?

Reading Time: 4 minutes 30 seconds


Date: 2022-05-10

Fasting comes with a lot of health benefits, from weight loss to improved insulin sensitivity. To follow a fasting diet strictly, you cannot consume any food during a specified period of time. 

But what about supplements? Do they count as food? This can be confusing even for experienced fitness and health buffs. If you work with clients who want to fast but also use supplements like BCAAs, learn how they impact the fasted state and whether it matters in the end. 

What is Fasting? 

Fasting is simply not eating. It means not consuming any calories for a period of time. People have long used fasting for a variety of reasons, including as part of spiritual and religious practices. 

Many people fast to lose weight or benefit their health. Research has backed up this practice, proving there are many benefits if done right. There are several different strategies you can use to fast for health reasons: 

  • 16/8. This is one of the most popular and sustainable styles of fasting. You fast daily for 16 hours and restrict your eating to an 8-hour window. A typical window for eating on the 16/8 fast is between 10 am and 6 pm. 

  • 5:2. On this diet, you fast two days per week and eat normally on the other five days. This is primarily a diet with weight loss as the goal. On the fast days, you eat 500 to 600 calories, so it isn’t necessarily a true fast. 

  • Eat-Stop-Eat. This is like the 5:2 diet, but on fast days you eat nothing for 24 hours. You can do it for one or two days per week. 

  • Individual. One of the good things about fasting is that it’s flexible. You can individualize your strategy and do what works for you. Vary the 16/8 diet or do 24-hour fasts once in a while. 

Help your clients achieve healthy weight loss with these pro tips

The Many Benefits of Intermittent Fasting

Intermittent fasting is a trending topic in diet, nutrition, health, and fitness. Its popularity continues to grow, and it might be more than a fad. This is an eating strategy that has the potential to stick around due to the many proven benefits

  • Improved cognition and memory

  • Lower blood pressure and resting heart rate

  • Lower LDL cholesterol and triglycerides

  • Lower risk of heart disease

  • Reduced inflammation

  • Weight loss and maintenance

  • Lowered risk of diabetes

  • Improved metabolic numbers, including insulin sensitivity

  • Reduced tissue damage

Intermittent fasting is safe for most people, but it’s always best to check with your doctor before trying a new diet. 

What Are Branched-Chain Amino Acids?  

The branched-chain amino acids, or BCAAs, are the essential amino acids that have a branched chemical structure: leucine, isoleucine, and valine. These are three of the nine essential amino acids that you have to consume because the body cannot produce them. 

BCAA supplements are popular with bodybuilders and others looking to build muscle. Muscle tissue is made up of amino acids, and these three in particular are involved in stimulating muscle protein synthesis. Research shows that a BCAA supplement after strength training increases muscle gains. 

Other potential benefits of supplementing BCAA include reduced muscle breakdown and soreness after a workout and reduced fatigue. In people at risk for muscle-wasting, BCAA can slow or reduce muscle mass loss. 

Check out this ISSA blog article to learn more about BCAA supplements

So, Do BCAAs Break a Fasted State? 

The straight answer is yes. Anything that provides calories technically breaks a fast. You can drink water or black coffee or plain tea without breaking a fast, but a food, drink, or supplement with calories counts. 

Do BCAAs Break a Fast to the Extent That You Should Avoid Them? 

There is no clear answer to this question based on research, although a quick search will lead to many so-called experts sharing their opinions. 

Some argue that a mere 20 calories from a BCAA supplement still gives you most of the benefit of a fast. Others would say that a fast is a strict no-calorie window and that you should not break it for anything. It’s likely that there is some truth to both arguments and that the answer depends on the individual. 

A fasted period allows insulin levels to drop. Insulin signals the body to store fat, so when it drops, the process reverses. Instead of storing energy as fat, you start burning fat. Would a small amount of calories be enough to interrupt this? The answer isn’t clear, but you likely still get many metabolic benefits of the fast, even with the supplement. 

Skipping BCAAs During a Fast Depends on Your Goals

The fact that BCAAs speed muscle growth and that fasting can be good for health, presents a conundrum for many people. Is it worth breaking the fast for a few protein calories that might help you build more muscle?

Whether or not you use BCAA supplements during a fast is a personal decision for you or your client. Consider your goals and how the break in your fast might affect them. For example, if your goal is to change body composition by losing fat and building muscle, you might want to break the fast slightly to use BCAAs. 

Working out strenuously and limiting calories can help you lose fat, but if you aren’t consuming enough protein, you’ll also lose muscle tissue. This can sideline your goals, so you might want to compromise the fast just a little to make sure you can build muscle mass, not lose it.

If you’re most interested in fasting for the metabolic, heart, and other health benefits, consider a stricter fast. One solution, if it works with your schedule, is to work out during your eating window so that you can get the benefits of a BCAA supplement. 

Fitting in a workout around your fasting schedule is easier if you are doing a version of the 16/8 fast. If your plan includes 24-hour fasts or days limited to 500 or 600 calories, you might want to avoid exercising on those days. Use them as rest and recovery days. 

If you’re strictly fasting, avoid BCAA supplements in your fasted state. If you’re not concerned about a strict fast and want to build muscle, the supplement can support your goals. With clients, it’s important to consider their fitness and health goals before advising them on fasting and supplements. And, of course, always ensure they talk to their doctor before trying either.

Educating Yourself and Your Clients

Supplements can have important health benefits and help you meet fitness goals. Be aware of how a supplement affects other strategies, like fasting. BCAAs can be great for building muscle, but they will interrupt a fasted state. 

Become an ISSA-certified nutritionist and you’ll be prepared to answer every food question. ISSA’s Nutritionist program is an essential course in nutrition, diet, and health. It will prepare you to start coaching clients and helping them make better food choices. 


Intermittent Fasting: What is it, and how does it work?. Retrieved 8 April 2022, from

Jackman, S. R., Witard, O. C., Philp, A., Wallis, G. A., Baar, K., & Tipton, K. D. (2017). Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans. Frontiers in physiology, 8, 390.

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