Amino Acid Supplements: Not Everything They're Cracked Up to Be

What's left once protein is digested? Amino acids. And as the U.S. National Library of Medicine explains, amino acids are used to perform many body functions. But does that mean amino acid supplements are good for your health?

​Read more:​ The 9 Essential Amino Acids and Why Your Body Needs Them

"Amino acid supplements are sold with the promise of doing many things," says Connie Diekman, MEd, RD, a St. Louis, Missouri-based food and nutrition consultant, former president of the American Dietetic Association and former director of university nutrition at Washington University in St. Louis. "They promise to increase muscle mass, boost energy, fight infection, aid growth and more."

"But while there is research to show benefit, the question is if people need to consume them," Diekman says. "Most Americans consume adequate protein. And amino acids are the building blocks of protein. Even vegetarians and vegans can meet their protein needs through diet if they include plenty of plant proteins like beans, nuts, soy and products made from these foods. So whether people need to consume a supplement is doubtful."

But if amino acid supplements are on your radar, Diekman strongly advises first consulting with a registered dietitian or certified specialist in sports dietetics (CSSD). And, in the interim, familiarize yourself with the various types and some caveats to consider.

The amino acid L-arginine is found in red meat, fish, soy, chicken, whole grains, dairy and beans, notes the Mayo Clinic.

The Office of Dietary Supplements (ODS), part of the U.S. National Institutes of Health, says that makers of arginine supplements claim they can be a boon to athletes by boosting blood flow and oxygen delivery, while stimulating muscle growth. However, ODS says there's little scientific evidence to back that up, with most research suggesting that L-arginine doesn't deliver on its promises.

But ODS notes that, when taken at a dosage of up to 9 grams a day, it appears to be safe, at least for a period of weeks, though there have been reports of side effects such as diarrhea and nausea. The Mayo Clinic agrees that the supplement is generally safe, and even acknowledges that it might have some positive effects, such as lowering blood pressure and treating erectile dysfunction.

However, beyond warning of side effects such as nausea, diarrhea, abdominal pain, bloating, gout and a worsening of asthma symptoms, the Mayo Clinic cautions against taking it if you've had cold sores or genital herpes as it can trigger outbreaks. People taking blood pressure medications should also steer clear, the Mayo Clinic adds, as should those who've had a heart attack, out of concern that the supplement might lead to fatal complications.

Methionine is another essential amino acid. And according to the University of Rochester Medical Center (URMC), some manufacturers claim that, in supplement form, it acts as an antioxidant, detoxicant and a protectant against liver damage. Others argue that it can boost energy, treat osteoporosis and prevent early balding.

The problem? None of that has been proven, says URMC, though methionine supplements have been shown to cause nausea, vomiting, dizziness, drowsiness, low blood pressure and irritability. Taking it may also up your risk for heart disease, warns URMC, and pregnant women, those who are breastfeeding and people with bipolar disorder are urged to avoid it.

Supplement-makers claim that branched-chain amino acids (BCAAs) — which include leucine, isoleucine and valine — are energy-boosters, ODS notes. But has that been proven? There haven't been many studies, and the results are mixed. Some research indicates it might help athletes get stronger and pack on muscle mass, but ODS says there's little evidence it confers any aerobic boost to endurance athletes.

As for safety, ODS says that there doesn't appear to be a problem with daily doses up to 20 grams.

However, a study published in the journal ​Hypertension​ in October 2019 found that high concentrations of BCAAs were associated with a higher risk for high blood pressure among more than 4,000 middle-aged men and women tracked for about eight years. That investigation looked at circulating blood levels of BCAAs, rather than specifically at the impact of BCAA supplements, but it could be an indication that BCAA supplements might not be a good fit for everyone.

​Read more:​ How to Get Needed Protein Without Risking Your Heart Health