A lot of us use some kind of supplement to help gain an edge in life and love—whether it’s to get slightly bigger muscles (whey protein), improve cardiovascular health (fish oil), increase alertness and focus (caffeine), etc. Some work really well, others offer an incremental improvement, and the rest don’t do much at all. And how you pair supps can also increase or decrease their potency, like combining stacks of creatine and beta-alanine increases their muscle-building properties or mixing calcium and iron together creates competition among them for absorption by the body, limiting their efficacy.

Branched chain amino acids, or BCAAs, are leucine, isoleucine, and valine, and they are used to increase muscle mass and battle fatigue, but a new study published in Frontiers in Physiology has found that they may not work so well on their own. For the small study, researchers put 10 trained lifters through experiments where they downed a BCAA drink (5.6g) or placebo and did some one-rep max leg extensions and legs presses. They then took muscle biopsies and found that though the BCAAs did increase muscle protein synthesis rates by 22%, it didn’t compare to when a whey protein supp with a similar amount of BCAAs was taken. In that case, the muscle synthesis response doubled.

“Our results show that the common practice of taking BCAA supplements in isolation will stimulate muscle protein synthesis—the metabolic mechanism that leads to muscle growth—but the total response will not be maximal because BCAA supplements do not provide other amino acids essential for the best response,” said study lead Kevin Tipton, professor of sport, health, and exercise science at the University of Stirling in England. “A sufficient amount of the full complement of amino acids is necessary for maximum muscle-building, following exercise. Athletes interested in enhancing muscle growth with training should not rely on these BCAA supplements alone.”