You’ve probably heard people talk about taking amino acid supplements, but what are they, and are they good for anything? Essential amino acids can only be acquired by eating protein; these include histidine, lycine, methionine, phenylalanine, threonine, tryptophan, isoleucine, leucine, and valine. If you’ve ever heard the term “complete protein,” it means that a food contains all nine essential amino acids. Meat, poultry, fish, eggs, and dairy are complete proteins, as are quinoa, soy, hempseed, and buckwheat. A few amino acids are “conditionally essential,” meaning that they are only essential for specific subgroups of people; for example, arginine is necessary for children but not to adults.
Some of the essential amino acids are branched-chain amino acids (leucine, isoleucine, and valine), which skip the normal digestive processes and become available in the muscle to be used as energy or saved in a pool for later metabolism.
The essential amino acids are critical for the synthesis of muscle. Sarcopenia, wasting, and cachexia are the result of essential amino acid deficiency. Taking essential amino acids might help a person to prevent muscle loss while they are losing weight and eating a low-calorie diet. In mice, chronic essential amino acid supplementation increases lifespan, by reversing the decline of mitochondria in cardiac and skeletal muscle that occurs with aging.
Clinically, branched-chain amino acids are used to improve messaging in the brain cells of people with advanced liver disease, mania, anorexia, and tardive dyskinesia (a movement disorder). They have also been utilized in reducing muscle wasting among individuals confined to bed or with wasting-cachexia syndrome from diseases, including chronic obstructive pulmonary disease (COPD).
Contrary to popular advice at gyms, it is unlikely that taking branched-chain amino acids alone will have any beneficial effect on muscle growth. Athletes are advised to look for supplements that contain all nine of the essential amino acids are are composed of 20-30% leucine, which is a branched-chain amino acid believed to stimulate muscle protein synthesis the most of all of the amino acids. Older adults looking to prevent muscle loss should look for supplements that consist of 40% leucine.
Taking amino acid supplements is not necessary for most people, however, since they are found abundantly in a variety of foods. Examples of foods high in leucine include turkey, beef, fish, soybeans, eggs, white beans, and kidney beans.
Research published in the Journal of Diabetes in May 2018 found that those who develop type 2 diabetes and heart disease have higher levels of the branched-chain amino acids; more research is needed. Side effects of branched-chain amino acid supplements include fatigue and loss of coordination, as well as stomach problems. Rarely, these supplements have resulted in high blood pressure and headache. The only essential amino acid with known toxicity is methionine, which is transformed into the toxic metabolite homocysteine and can cause atherosclerosis.