What Happens to Your Muscles When You Take Amino Acid Supplements?

Amino acids are often called the building blocks of protein, which help your body perform essential functions like growth, digestion, and tissue repair. Your body produces 11 amino acids naturally, while the other nine, called “essential” amino acids, must come from protein-rich foods like meat, eggs and dairy.

Supplements are another option, and they are popular among people looking to improve their fitness. Studies on their effectiveness are limited, but here are three things that could affect your strength and exercise performance when you take amino acid supplements.

There is little evidence that amino acid supplements alone will make your muscles grow. If you’re already meeting your daily protein needs through healthy, whole foods, you’re already getting the amino acids needed for muscle growth, said Anthea Levi, MS, RD, registered dietitian and founder of ALIVE+WELL Nutrition. In this case, taking a supplement is unlikely to provide additional benefit unless you’re training at high intensity, added Emily Hernandez, MS, ACSM, a certified exercise physiologist at Orlando Health.

That said, some research suggests that taking daily branched-chain amino acids (BCAAs) — leucine, isoleucine, and valine — about 30 to 45 minutes after resistance exercise can temporarily boost muscle protein synthesis, the process by which muscles repair and grow. This effect is thought to occur through activation of the mTORC1 pathway, which helps trigger muscle-building processes, Levi explained.

Although the evidence is inconclusive, amino acid supplements, particularly BCAAs, may help reduce fatigue during long or intense workouts, Hernandez said. A small clinical trial found that combining moderate exercise with BCAA supplementation for eight weeks improved strength, mobility and endurance in older adults.

During exercise, muscle tissue develops small microtears that promote its growth over time. Some clinical trials indicate that BCAAs may help relieve soreness during this process, which could be particularly helpful for those who are new to exercise or who regularly train at high intensity, Hernandez said. Other studies, mostly in animals, suggest that taking glutamine, the most abundant amino acid in the body, may also relieve pain.

Still, it’s important to remember that no supplement can replace a quality, balanced diet, Hernandez emphasized.

Experts recommend talking to a healthcare professional before taking amino acid supplements. In most cases, they’re not necessary if you’re already meeting your daily protein needs through your diet, Levi said. Foods rich in protein and amino acids include lean meats like chicken and turkey, soy, nuts, seeds, beans, and fish like salmon and tuna.

Amino acid supplements are generally well tolerated, said Shannon O’Meara, MS, RD, LDN, a registered dietitian at Orlando Health. The people most likely to benefit are people who are new to exercise, people who train at high intensities and older adults who may suffer from age-related muscle loss, Hernandez said.

That said, amino acids aren’t for everyone. Children, pregnant or breastfeeding women, and those with underlying health conditions like diabetes or liver disease should avoid these supplements. Possible side effects include:

• Nausea
• Diarrhea
• Muscle cramps
• Dehydration
• Headaches
• Confusion
• Liver and kidney complications

Because dietary supplements are not regulated by the U.S. Food and Drug Administration, experts recommend choosing products that have been tested for purity and label accuracy by organizations such as the United States Pharmacopeia (USP) or the National Sanitation Foundation (NSF).