BCAAs: myth or reality?

BCAAs — leucine, isoleucine and valine — take up an entire shelf in every sports nutrition shop, often at a premium price. The promise: to build muscle and protect the muscle you already have. A 2017 scientific review asks the question right in its title: myth or reality? Its answer is damning. But the story doesn’t end there — BCAAs do have an effect, just not the one they’re selling you.

The study comparing BCAAs with real protein

This is the most telling comparison. In 2019, a randomised, double-blind trial divided 45 men aged 71 into three groups: 6 g of BCAAs, 6 g of branched-chain keto acids, or 30 g of milk protein. Muscle protein synthesis was then measured, not just once, but over two successive time windows.

BCAAs do, therefore, work in the strictest sense: they do indeed boost protein synthesis. But it’s a flash in the pan. Two hours later, levels have dropped back down, whilst whole milk protein is still having an effect. The authors state this clearly: the increase achieved with 6 g of BCAAs is short-lived, unlike that achieved with an equivalent amount of intact milk protein.

The harshest verdict

The 2017 review goes further than simply describing the approach as ‘less effective’. It first notes a gap: at the time of its publication, no study had quantified the response of muscle protein synthesis to BCAAs taken orally on their own in humans. The entire commercial claim was therefore based on a lack of experimental evidence.

And the only two studies that had tested BCAAs on their own, administered intravenously, found that they reduced muscle protein synthesis — whilst also reducing protein breakdown. The authors’ conclusion is unequivocal: presenting BCAAs as a stimulant of muscle protein synthesis in humans is not justified.

A 2019 biochemistry review is slightly less definitive: it describes the evidence as inconclusive rather than non-existent. On this specific point, therefore, the literature is not unanimous — but no one is arguing that there is a clear-cut effect.

What about leucine on its own?

This is the fallback argument: that leucine is the ‘trigger’ amino acid. There is some truth in this in the short term. A 2006 study involving 20 men aged 70 added leucine to balanced meals and measured muscle protein synthesis over a five-hour period.

The difference is clear. Except that three years later, the same question was investigated over a longer period: 30 healthy older men took 7.5 g of leucine a day for three months. The result: there was no change in muscle mass or strength in either the leucine group or the placebo group.

That’s exactly the catch with this section of the shop: a genuine, acute effect – measurable in a laboratory over a few hours – which has absolutely no lasting effect on the body after several months.

Note: Leucine appears to be particularly useful for compensating for an inadequate meal. A 2006 study shows that enriching a mixture of essential amino acids with 41 per cent leucine restores the response in older people, whereas 26 per cent is insufficient — but that this enrichment offers no additional benefit in younger subjects. And when protein intake is already sufficient, adding leucine does not further increase muscle synthesis.

Where BCAAs really make a difference

Let’s give them their due. In two areas that have nothing to do with muscle building, studies do indeed find an effect.

Muscle soreness and muscle damage. A 2021 meta-analysis of nine randomised trials involving trained men found a positive effect on creatine kinase (a marker of muscle damage) within 24 hours, at 24 hours and at 48 hours after exercise. As for muscle soreness itself, the effect was only evident within the first 24 hours, whilst another marker, lactate dehydrogenase, remained unchanged.

Mental fatigue in endurance sports. Several studies, including one from 1991 conducted during a 30-kilometre cross-country ski race and a marathon, report an improvement in mental performance after exercise, and a reduction in perceived exertion during exercise. The hypothesis put forward is that this has an effect on the brain — less tryptophan is absorbed, and therefore less serotonin is produced.

In summary

The bottom line: BCAAs aren’t dangerous, they’re just redundant. If you’re meeting your daily protein intake, you’re already consuming plenty of them — and in a form that your muscles can utilise for longer.

To find out how much complete protein you should aim for and in what form, have a look at whey or natural proteins.

Every figure in this article is taken from the studies listed below, summarised on the basis of their abstracts alone. Please note the study populations: several of the trials on leucine involve older people, whose muscles respond differently, and the research on fatigue mainly concerns endurance sports. This is for information purposes only and is not a substitute for professional advice.