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Essential amino acids (EAA)

The nine amino acids your body can't make — and the real drivers of muscle protein synthesis.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsAmino acidsMuscleProtein

Of the 20 amino acids that build our proteins, nine are essential — we must get them from food. They are the actual signal and substrate for building muscle, which is why EAA powders have become popular. For most people, though, enough quality protein does the same job.

Key takeaways

  • The nine EAAs (including the three BCAAs) must come from the diet and are what actually trigger and sustain muscle protein synthesis (MPS).
  • A full spread of EAAs raises MPS more than BCAAs alone — you need all nine to build protein, not just the “switch”.1
  • Most useful when protein intake or quality is low — older adults, plant-based diets, or training fasted.
  • For most people, whole protein (whey, dairy, meat) supplies the same EAAs more cheaply.

What they are

The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Because the body cannot synthesise them, a shortfall of any one limits how much protein you can build — the “weakest link” principle.

The evidence

EAAs stimulate muscle protein synthesis in a dose-dependent way, and the response depends on getting all nine together with enough leucine to trigger it. The International Society of Sports Nutrition concludes that EAA-rich protein around training supports muscle adaptation.1

Dose & how to use

Studies typically use ~6–15 g EAA containing ~2.5–3 g leucine, taken between meals or around training. There is no advantage to EAAs if a meal already delivers that much high-quality protein.

Safety & who benefits

Safe for healthy adults. Genuinely useful for older adults (who need more leucine to overcome “anabolic resistance”), plant-based eaters, and clinical or appetite-limited situations. Otherwise a protein-rich diet already covers it.

Bottom line: the real muscle-builders — worth it when protein is low or quality is poor, redundant when your diet already delivers enough.

References

Adult research summary for education, not a prescription. These are food supplements, not treatments for disease.

  1. Jäger R, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 2017. pmc.ncbi.nlm.nih.gov

This article summarises nutrition and exercise science for education. It is not a substitute for individual medical advice; consult a professional before starting a supplement, in pregnancy, or alongside medication.