Taking branched-chain amino acids (BCAAs) while fasting intermittently can have significant benefits, especially for body composition. While intermittent fasting, the eating window is shortened, making it difficult to get the nutrition and meals your body needs. But will BCAAs interrupt intermittent fasting? Here’s what you need to know: 

Do BCAAs Break a Fast?  

It’s no surprise that we get asked this question often here at aminoVITAL. With the increasing popularity of fasting and intermittent fasting in the fitness industry, the benefits of fasting are becoming more well-known. It’s also no surprise that those who usually use BCAAs to prevent the breakdown of their muscles and reduce their soreness are now interested in whether these branched-chain amino acids affect their progression and break their fasting efforts.  

The short answer is yes. BCAA’s technically do break a fast. However, there is an important distinction: BCAAs do not reduce the potential health benefits of fasting.  

Why do people fast? 

People fast for a variety of reasons. Some practice fasting as part of their religion or spiritualities, often considered an act of sacrifice as it cleanses and purifies the body. Some think it is an effective way to lose weight short-term, and some fast simply as a way to detoxify their body in general or for an upcoming medical procedure.  

Despite the ever-growing trend of fasting and the surge in popularity, fasting is a concept that dates back hundreds of years and is defined as abstinence from food and drink for set periods. In contrast, intermittent fasting is cycling between periods of eating and fasting, ranging from a few hours to a few days at a time.  

What are the benefits of fasting? 

There have been several science-backed studies that have found that fasting does have significant benefits to our health. For example, studies have found that fasting has many benefits to brain function. One study in mice showed that when they were exposed to fasting for 11 months, they experienced improved brain structure and function. And there have been other studies that have shown that fasting can protect the health of the brain overall.  

Intermittent fasting could also decrease blood sugar levels and help decrease insulin resistance. According to a study from the US National Library of Medicine and the National Institute of Health, intermittent fasting has significantly reduced blood sugar levels in those with type 2 diabetes.  

Intermittent fasting could also help the human body hold onto muscle mass. This is because muscle is a metabolically active tissue, which allows our bodies to burn calories even when resting. Unfortunately, when people lose weight, they can also lose muscle. There have been some studies that have shown that intermittent fasting could preserve muscle mass. A 2011 study and review showed that intermittent fasting was potentially more effective at holding on to muscle during weight loss than a traditional calorie deficit.  

These are just a few benefits backed by science about fasting in general. But how do BCAAs play into this concept?   

How do BCAAs work while fasting? 

As we mentioned earlier, BCAAs technically do break a fast, but not in the same way that other foods and drinks will. A fast is broken when we consume anything that has a caloric value. The insulin we get from consuming food helps transfer those nutrients from our meals to the appropriate places. When we consume calories, specifically in the form of glucose, it triggers an insulin response that helps our bodies transport those calories throughout the body to use for energy. In a nutshell, our bodies use predominately fat as an energy source during fasting instead of using carbohydrates, which triggers an insulin spike.  

However, BCAAs do not trigger this insulin spike. They only trigger a slight insulin response in the body, and it’s not enough to switch the body out of a fat-burning state. A study from the National Library of Medicine showed only a modest insulin response after the ingestion of 1g and 5g of BCAAs.  

So, knowing all of this, why take BCAAs in the first place? Because they help reduce fatigue and muscle soreness and keep you performing at your best.  

Fatigue is one of the hardest things to overcome while fasting, especially if you engage in any type of fasted workout.  

If you are exercising in a fasted state, then your glycogen stores will be low, which means you are going to feel fatigued faster than if you had recently eaten. BCAAs can help reduce this effect and can increase exercise capacity. 

This is a huge benefit to those in a fasted state because they’re already putting their body through stress by withholding food. BCAAs can help mitigate some of the central fatigue that comes with fasting and fasted exercise.  



Arnason, T. G., Bowen, M. W., & Mansell, K. D. (2017). Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot study. World journal of diabetes, 8(4), 154–164. https://doi.org/10.4239/wjd.v8.i4.154 

Insulin. (2018, March). YourHormones.com. Retrieved from http://www.yourhormones.info/hormones/insulin/ 

Li, L., Wang, Z., & Zuo, Z. (2013). Chronic intermittent fasting improves cognitive functions and brain structures in mice. PloS one, 8(6), e66069. https://doi.org/10.1371/journal.pone.0066069 

Link, R. (2018, July 30). 8 Health Benefits of Fasting, Backed by Science. Healthline.com. Retrieved from https://www.healthline.com/nutrition/fasting-benefits 

Zhang, Y., Kobayashi, H., Mawatari, K., Sato, J., Bajotto, G., Kitaura, Y., & Shimomura, Y. (2011). Effects of branched-chain amino acid supplementation on plasma concentrations of free amino acids, insulin, and energy substrates in young men. Journal of nutritional science and vitaminology, 57(1), 114–117. https://doi.org/10.3177/jnsv.57.114 

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