BCAAs: Why the hype outpaces the evidence

When Prof. Stu Phillips and I sat down to talk BCAAs, we knew we might ruffle feathers. Few products have ridden a longer wave of marketing than branched-chain amino acids—leucine, isoleucine, and valine. They’re three of the nine essential amino acids (EAAs), meaning we must get them from food. The question athletes actually need answered is simple: do BCAA powders do anything extra if you already eat enough high-quality protein? After revisiting the literature (and hearing Stu’s take as someone who generates much of that literature), my answer is equally simple: for most athletes, no.

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HISTORY

Let’s start with why BCAAs sounded so promising. Muscle tissue is relatively enriched in these amino acids, and leucine in particular acts like a foreman on a worksite—it arrives and tells the crew to start building. Biochemically, leucine helps switch on mTORC1 and initiates muscle protein synthesis (MPS). That “leucine trigger” is real, which is one reason why leucine-rich proteins (whey, dairy) are great choices around training. But a trigger isn’t a full build: once you shout “Go!”, you still need a steady supply of all the EAAs to lay bricks and keep MPS going. BCAA-only blends, by definition, don’t provide the complete set of building blocks.

Human tracer studies make this point clearly. Give people a suboptimal dose of protein and you can “rescue” the MPS response by adding leucine or an EAA mix. In other words, if your protein feeding is too small, boosting leucine (or taking EAAs) can bring the response closer to that of a full serving. Useful? Yes—for small, inadequate feedings. But when you compare BCAA-only versus complete protein or EAAs head-to-head, BCAAs consistently produce a smaller and shorter-lived anabolic response. Mechanistically, you’ve flipped the switch without supplying enough amino acid “bricks” to sustain construction.

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REAL-WORLD OUTCOMES

What about real-world outcomes? A comprehensive meta-analysis shows protein supplementation supports training adaptations to at least 1.6 g/kg/day is required for exercising individuals. Male or female, young or older. Higher amounts are recommended for endurance athletes - at Fuelin we opt for 2.0-3.0g/kg to ensure optimal protein intake. There’s no evidence that layering BCAA powders on top of an already adequate protein intake produces extra muscle or strength gains. If anything, it adds cost without a clear signal. Food first; top up with complete protein (whey/soy/pea) as needed.

Soreness and “muscle damage” markers are often touted as BCAA wins. The best you can say is that results are mixed and context-dependent. Recent systematic reviews report that BCAAs can attenuate certain blood markers (e.g., CK) and sometimes reduce DOMS after strenuous protocols—but effects are small to moderate, heterogeneous, and frequently vanish when you compare against active controls like carbohydrate or complete protein. Even where you see a blip, it’s not superiority to simply meeting protein needs. In practice, athletes do better by nailing daily protein and carbohydrate around sessions than by sipping flavored BCAAs and hoping for magic. ‍

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PERFORMANCE CLAIMS?

Performance claims? The International Olympic Committee’s consensus statement remains the most balanced, evidence-based guide. The IOC lists a short roster of ergogenic aids with strong support—carbohydrate, caffeine, creatine, beta-alanine, sodium bicarbonate. BCAAs aren’t on that list. That doesn’t mean they’re “bad”; it means, when standards are high, they don’t meet the bar for reliably improving performance in trained humans. As a coach and practitioner, that matters more to me than any single study.

Two common rebuttals deserve a straight answer. First, “I sip BCAAs when fasted so I don’t lose muscle.” Physiologically, amino acids—especially leucine—are insulinogenic. They elicit insulin release and interrupt the very hormonal milieu you’re chasing with a “clean fast.” If your aim is a true fast, BCAA sipping breaks it; if your aim is muscle retention during long gaps, a small complete protein feeding is a smarter intervention.

Second, “BCAAs help me feel better after training.” Placebos are powerful, and feeling better is not trivial. But when we zoom out to biomarkers and performance, the picture doesn’t justify the expense for most athletes who already meet protein targets. If a flavored drink helps you hydrate and eat on time, great—make that drink a whey, soy, or pea isolate (or just milk and fruit) and you get the taste plus the complete amino acid profile your muscles actually need.

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ANY USE AT ALL?

Are there scenarios where a BCAA-style approach has a role? Edge cases exist: severe appetite suppression, long-haul travel, or brief windows where you can’t stomach a full serving of protein. Even then, evidence favors EAA blends or complete protein over BCAA-only formulas, because they provide the full complement of indispensable amino acids. In older or clinical populations with anabolic resistance, leucine-enrichment of small protein doses can help—again, that’s about fixing an inadequate feeding, not outperforming a normal, protein-adequate diet. For healthy, well-fed endurance and strength athletes, BCAAs remain a solution in search of a problem.

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BOTTOM LINE

My bottom line as a coach and co-founder at Fuelin is pragmatic: invest where the effect sizes are real. Hit ~0.3 g/kg protein at 3–5 meals/snacks per day (which naturally delivers ~2–3 g leucine per feeding if you choose high-quality sources) OR simply your daily Fuelin recommendation of 2-3g/kg of protein daily! Wrap training with appropriate carbohydrate. If you use supplements, choose those with consistently positive, sport-relevant outcomes—caffeine, creatine, beta-alanine, bicarbonate—and use them at evidence-based doses. For nearly everyone already eating well, BCAAs are a distraction. Good marketing, sure. Good return on your dollar? Not in my program.

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Thanks for reading,

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Scott

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