will BCAA's break my fast?

Will BCAA’s Break My Fast?

In the fitness industry, intermittent fasting is a popular choice due to its abilities to increase fat burning, improve insulin sensitivity, and increase HGH (human growth hormone). All these attributes make intermittent fasting a popular choice among gym goers, fitness enthusiast, or simply anyone who wants to stay in shape. However, a main concern among those who intermittent fast and workout is that they do not want to lose any muscle.

So a lot of people decide to drink BCAA’s (branched-chain amino acids) while they fast…The question is, will these amino acids break your fast?

I often get asked about acceptable drinks while fasting, and one of the most popular drinks people want me to discuss is BCAA’s. There has been some debate on whether or not BCAA’s are acceptable while intermittent fasting. I will be discussing if BCAA’s do indeed break your fast, benefits to drinking BCAA’s while fasting, and the best BCAA’s for intermittent fasting.

What Are BCAA’s?

First, I want to clarify what exactly branched chained amino acids are, and what they do. Branched-chain amino acids are the essential amino acids (leucine, isoleucine, valine), and these amino acids are responsible for your a large portion of your body’s muscle protein. They are called essential amino acids because your body does not produce them on its own, whereas, nonessential amino acids are produced by the body. Thus the name “nonessential”.

will BCAA's break my fast

Amino acids often get called “the building blocks of protein”. That is because a protein is basically multiple amino acids held together by peptide bonds. This makes them a popular choice among weightlifters or athletes due to their ability to build protein molecules.

What Do BCAA’s Do?

Most people who consume BCAA’s are weightlifters, athletes, runners, or anyone interested in building/preserving muscle mass. BCAA’s are taken to help enhance muscle protein synthesis and recovery following a workout. Essential amino acids are very important in muscle building and recovery, making them a popular choice for anyone who is constantly breaking down their muscles from a workout.

Branched chain amino acids also play an important role during training. This is due to their ability in helping preserve muscle glycogen, which is the fuel source of your muscles during activity. So amino acids help fuel your muscles, as well as protect your muscles during intense workouts by preventing muscle catabolism (breakdown).

Will BCAA’s Break My Fast?

BCAA’s have been recognized as an amazing drink for intermittent fasting, due to them containing zero calories, and the muscle benefits listed above. Especially during intermittent fasting where you are not consuming any food (specifically protein) which your muscles need to recover & grow. So everyone turned to BCAA’s as their savor to avoid muscle breakdown while still fasting. However, BCAA’s technically break your fast! Let me explain why.

This is primarily due to the essential amino acid “Leucine”, which is the main amino acid responsible for activating protein synthesis. Leucine is the main amino acid that is responsible for activating protein synthesis pathways to your muscles. The problem with Leucine is that it also activates similar pathways in the brain, and MOST of the benefits of intermittent fasting take place in your brain. Research has shown that the amino acid “Leucine” activates these pathways in your brain, and will make your brain believe you have consumed food. Your brain makes use of Leucine as an indicator for whether or not you have been fed.

So technically, if you drink BCAA’s while fasting, your brain will believe you have broken the fast. Even though you haven’t consumed calories, Leucine will trigger pathways which tell your brain you have been fed. Therefore, this would “turn off” the neurological benefits of intermittent fasting such as cellular autophagy, neuro-protective factors, and longevity. For this reason, I recommend not drinking BCAA’s while fasting. One of the main reasons for doing intermittent fasting is for the neurological (brain) benefits such at cellular autophagy, neuron enhancements, protective mechanisms, and improvements in longevity. So by consuming amino acids you would technically be shutting down these benefits.

What About If I Workout Fasted?

A main concern for those who workout in the morning is that they would be training while they are still fasted. Those who workout while fasting are concerned of muscle breakdown. This is true, that muscle breakdown can occur during training especially while fasting. For this reason, I recommend people workout/train during their feeding window. However, it is not as problematic as you think.

For example, say you follow the 16:8 intermittent fasting protocol, and you usually eat from Noon to 8pm. That means you are fasted from 8pm until Noon the next day. Let’s say you like to workout at around 6-7am, and then you would be done by 9-10am. This means you would workout, and still be required to fast 2-3 more hours to reach Noon, and your 16 hours of total fasting. This is OKAY, your muscle tissue will not suffer as drastically as you think, especially if you break your fast at Noon with a high protein meal. During a fasted workout you will be using primarily body-fat for your energy source, before even muscle breakdown takes place. This actually is a great way to lose unwanted body-fat.

Like I said, I recommend lifting weights while you are in your feeding window to avoid this, but if you absolutely have to workout while in your fasting window, then you could consume amino acids during the workout (to avoid muscle breakdown). Technically, it will break your fast (at least neurologically), but you still will be getting the fat burning effects, and the effects from not eating.

BCAA’s That Won’t Break Your Fast

will BCAA's break my fast

If you are still concerned of losing muscle mass while training fasted, there are a few options for you. Amino acids/supplements such as beta alanine, creatine, L-carnitine, and betaine DO NOT break your fast. This is because these amino acids are not responsible for protein synthesis, unlike Leucine. So, if you want to take some supplements before or while training then I recommend one of the supplements I listed above.

Beta alanine and Betaine are amino acids that do not break your fast, and can be taken before, during, or after your workout. These amino acids can help with muscle strength and energy during your workout. Creatine and L-carnitine are also supplements that can be taken before, during, or after workouts, and they DO NOT break your fast. Creatine and L-carnitine provide energy during workouts, and has been shown to increase muscle workload output during exercise. Check out my complete list of supplements acceptable during intermittent fasting here.

TheMuscleMaster’s Final Say:

If you want to be strict with intermittent fasting, then you should not consume BCAA’s during your fast. Rather stick with acceptable drinks while fasting to ensure you are getting all the benefits! I recommend working out while in your feeding window to avoid any chance of muscle breakdown. However, if you absolutely have to workout while fasting, then I recommend you drink some form of BCAA’s. Sipping on amino acids while you workout will not dramatically hinder your results from intermittent fasting.

You can still consume non-proteinogenic amino acids while fasting such as beta alanine, betaine, creatine, and L-carnitine. These amino acids will not break your fast, and make an excellent choice. These amino acids can help with your workouts while still maintaining your fast!

Check out my full guide on the best supplements to take that won’t break your fast.


  1. Thanks for this article! This was the answer to my question I’ve been searching for and very informative!

  2. Very informative! What if I break my fast with the bcaa right after a workout? I fast 20 hours, work out after work, then have my window of eating.

    1. Author

      Hey Andrew,
      That would be fine..Breaking your fast with BCAA’s would actually be very beneficial, it is a great way to transition quickly from a catabolic to an anabolic state. Which would help prevent muscle loss and build muscle.

  3. Thanks for the info! What about adding L-Glutamine to water while fasting, do you think one teaspoon will break a fast?
    Thanks in advance.

    1. Author

      Hey Michelle,

      Good question, L glutamine is a proteinogenic amino acids meaning it is used to synthesize protein in the body. Although, one teaspoon is a small amount, it technically would break your fast. I only recommend amino acids that aren’t proteinogenic while fasting. These are betaine, beta-alanine, D-aspartic acid, carnitine, and creatine.

  4. Thanks for the very informative article! Do you think the leucine in micellar casein (which is 2.2g for Muscletech’s Nitro Tech Casein Gold) is enough to trigger our MTOR or is it enough to trigger protein synthesis (thus breaking the fast ) considering that that 2.2g of leucine will be spread out to 8 hours of digestion?

    1. Author

      Hey Noar,
      Great question, yes 2.2grams of leucine is a substantial amount, and enough to trigger mTOR signaling pathways even without insulin stimulation. Besides just the leucine, the milk protein isolate and casein protein will trigger protein synthesis breaking your fast. I would stick to consuming this in your feeding window, and would be okay to consume before you start fasting.

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