Amino acids are among the most versatile of all supplements. They can help people increase muscle and improve moods, and also provide a convenient non-animal source of amino acids for vegetarians. Yet aside from their place in many body-building supplements, amino acids tend to take up very little shelf space. Knowing some of the research behind the supplements will help you connect customers with their benefits.

What they are
Amino acids are the building blocks of protein. After water, amino acids are collectively the most common substance in the body. Ten dietary amino acids are "essential" because the body cannot make them: L-arginine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan and L-valine. All other amino acids are considered nonessential because the body can make them. However, some people have difficulty making or absorbing them.

The research on building muscle
The most exciting recent research has focused on the role of multi-amino-acid supplements and single-amino-acid supplements in building muscle in seniors.

• Multi-amino acids. Recent studies show that multi-amino-acid supplements, which provide eight to 11 free—or unbound—amino acids, can reverse sarcopenia, the age-related loss of muscle. In one of the studies, published in the American Journal of Cardiology, daily multi-amino-acid supplements increased lean body mass—i.e., muscle—after six months and even more so after 16 months.
• Branched-chain amino acids. L-leucine is one of three branched-chain amino acids that help convert protein to muscle. BCAAs account for about one-third of the protein in skeletal muscle. In a recent European study, taking 3 grams of leucine daily boosted muscle synthesis in older men to almost the same level as that in young men.
• Two more muscle-building aminos. L-ornithine can safely increase secretion of human growth hormone. Researchers reported that supplements of 2,000 milligrams daily increased the stamina of subjects riding exercise bikes. Beta-alanine, a precursor to carnosine—technically a dipeptide, closely related to an amino acid—also led to greater endurance and less fatigue on exercise bikes.

  The research on mood
  Several amino acids form the basis of neurotransmitters—brain chemicals that influence mood and cognitive abilities.

• L-tryptophan. This amino acid and its 5-HTP form are the building blocks of the neurotransmitter serotonin, which protects against depression and anxiety. A study conducted at McGill University in Montreal found that L-tryptophan supplements (1 gram, three times daily for 15 days) led to less irritability and "quarrelsome" behavior.
• Gamma aminobutyric acid. GABA is also a neurotransmitter that helps the brain filter out extraneous and distracting stimuli. As such, it can have a calming effect, reducing anxiety and racing thoughts.
• L-theanine. Found in green and black tea, L-theanine increases alpha waves in the brain, leading to improved mental focus and a feeling of relaxation. The effect is similar to that of meditation and yoga.
• N-acetylcysteine. Recent studies show that this particular form of the amino acid L-cysteine can reduce addictive behaviors, such as cocaine use and gambling.
• L-arginine. This amino acid is the precursor to nitric oxide, which regulates blood-vessel tone and flexibility and can often lower blood pressure. Because poor blood-vessel tone is involved in erectile dysfunction, L-arginine may function as a safe, natural sexual enhancer for men. Jack Challem is a personal nutrition coach in Tucson, Ariz. His latest book is Stop Prediabetes Now (Wiley, 2007). E-mail him with "NFM" in the subject line at jchallem@aol.com.