Risks of Using BCAAs to Burn Fat and Build Muscle

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J. E. Hinners, MD MPH

bellyBranched-chain amino acids (BCAAs) are often promoted in the world of bodybuilding as well as in various other workout routines as a means for accelerating the body’s ability to burn fat and build muscle. They are also claimed to improve your fitness endurance performance and reduce muscle soreness.

Part of the alluring appeal of these taking BCAA supplements is that they appear to be “natural,” as the body naturally makes BCAAs.

When taking any supplement, however, it is always wise to discerningly investigate any supplement-associated health risks in addition to the many benefits that advertisers are already telling us about. Surprisingly, even supplements that mimic the body’s natural components are not guaranteed to be free of adverse effects.

What are BCAAs?

Branched-chain amino acids (leucine, isoleucine, and valine) are substances that are found naturally in the body and are used for building proteins and nourishing muscle. Food sources of BCAAs include milk, meats, nuts, whey protein, fish, and eggs–or primarily protein sources.

As long as you’re not depriving your body of protein foods and you are generally a healthy individual without any particular disease conditions, then dietary intake of BCAAs is typically adequate for meeting the body’s need for BCAAs.

What are some medicinal therapeutic uses of BCAA supplementation?

  • Treating patients with liver disease (such as cirrhosis)–BCAA helps correct the liver’s amino acid imbalance
  • Treating those with anorexia, particularly from cancer or liver disease–BCAA is believed to stimulate the appetite
  • Treating post-surgery bed rest patients–BCAA supports the muscle recovery phase
  • Treating those suffering from tardive dyskenesia (a muscle movement disorder resulting from long-term use of certain antipychotic drugs)–BCAA appears to reduce symptoms

Why do athletes and dieters also consider BCAA supplementation?

Advocates of BCAA supplementation for athletes and dieters claim that BCAA supplementation improves fitness because it:

  1. Burns fat
  2. Builds muscle
  3. Reduces muscle soreness
  4. Increases athletic power & endurance
  5. Reduces cravings for sweets & carbohydrates (“by increasing serotonin levels,” to paraphrase)


What the Research Says for Those Taking BCAA Supplements for Fitness Reasons

There is a fantastic, scientific literature review of the research on BCAA supplementation here that I am using below (unless stated otherwise) because I don’t believe in reinventing the wheel. For specific scientific citations or for further explanation, please refer here.

Possible BENEFITS of BCAA supplementation:

1. BUILDS MUSCLE (anabolic effects of leucine)


3. May INCREASE PHYSICAL ENDURANCE at lower-moderate levels (as was found in one study at 50% dietary increase in the rats tested). This finding appears to be due to reduced glycogen depletion rates.

4. May MILDLY INCREASE PHYSICAL & MENTAL ENDURANCE for longer-lasting physical activity when taken in high doses above 50g over the course of multiple hours, as was tested in one study. One theory argues that BCAA loading prior to exercise in fact decreases serotonin production in the brain since BCAAs and serotonin share the same transport–thereby delaying onset of physical fatigue (**note the contrast with BCAA advocates’ claim about increased serotonin with BCAA supplementation).

5. May DECREASE MENTAL FATIGUE in aerobic exercise

6. May REDUCE MUSCLE SORENESS relative to carbohydrate ingestion

 At this point, you may be asking yourself…

“So what’s so bad about BCAA supplementation, then??”


Possible RISKS of BCAA supplementation:

1. May DECREASE exercise ENDURANCE at higher levels (at 100% dietary increase in the rats tested)

2. May–or may not–have a POSSIBLE LINK TO the development of Amyotrophic Lateral Sclerosis (ALS), a common neuromuscular disease sometimes referred to as “Lou Gehrig’s Disease.” The evidence for this possible link is very weak and not yet overwhelming. High correlations have been reported between football players and the development of ALS, and there is quite some discussion of the topic in Manuel’s article, “Stronger is not always better: could a bodybuilding dietary supplement lead to ALS?”

3. May lead to hyperaminoacidemia; the excess leucine (one of the three BCAAs) can THEORETICALLY WORSEN INSULIN RESISTANCE. Some well-respected health professionals express reserve for BCAA supplementation since insulin resistance can lead to Type 2 Diabetes, and the relationship between leucine and insulin resistance is still a bit unclear. Leucine deprivation and high leucine feedings have both appeared to improve insulin-resistant conditions in rats.

There has been somewhat mixed evidence pertaining to this point. Some studies suggest that those with high plasma BCAAs are at greater risk for developing diabetes, while one recent 2013 cohort study in Japan suggested that high oral intake of BCAAs may actually decrease risk of developing diabetes.

So I guess the conclusion on this particular point so far is…inconclusive.

My Personal Overall Opinion of BCAA Supplementation

As for me, personally, my preference would be to get my sufficient dose of BCAAs naturally from protein in my diet–meats, cheese, milk, fish, and nuts. For a helpful article on how to do that, read here.

I am not super comfortable with the possible link to increased insulin resistance (and possible development of diabetes) with BCAA supplements, and I’m not feeling super stellar about a questionable link with ALS.

That being said, I do suspect that those more in danger of possibly developing these potential side effects would be those who consume excessive amounts of BCAA supplements.

So if you really feel the need to take them, then at least make sure you are within the observed safety limits (and then even under those limits, to be more sure).

Dose limits for BCAAs

Men: 500mg/kg bodyweight (roughly 35g per day for the average male)


This gender data bias is a common and glaring fault in a number of medical and scientific studies–with many safety and dosage parameters set by male subjects. It really isn’t a political correctness thing here but a safety thing, as male and female bodies have their differences. So I would advise females to be well under the male limit to be safe.

*Whether male or female, and particularly if you have a special health condition or are taking medications–always “error” on the side of checking with your healthcare provider on dosage first!

Drugs used for Parkinson’s patients, for example, will be less effective if taken alongside of BCAAs.

Whey protein shakes–another alternative

If I felt the need to up my BCAA intake, I would probably feel a tad safer doing so by way of consuming a quality whey protein shake (with grass-fed cow milk!), as BCAA’s are naturally occurring in whey protein and are in a less concentrated form (some whey protein shakes disclose the amount of BCAAs per serving).

If you’re lactose-intolerant, you may be surprised to find that your body can tolerate whey protein with little to no problems, relative to other lactose-containing products, depending on which whey protein product you buy. Some contain more lactose than others, so a bit of product label investigation would be in order, alongside consulting a healthcare provider, if needed.

Here are the two whey protein shakes I have had–both by Dr. Mercola, so I may be a bit biased here, but I loved them both and took them for different reasons:

Dr. Mercola: Miracle Whey Banana Protein Powder 1 lb


Dr. Mercola: Pro-Optimal Whey – Chocolate 19.05 oz

Big fan of the banana-flavored one (Miracle Whey), but I also liked the extra immune support of the Pro-Optimal Whey. Dr. Mercola discusses a bit more about whey protein shakes here.

Well, that’s about it on BCAA supplementation. Have you had any personal experiences, good or bad? Do share, we’d love to hear about it!