Journal Title (Medline/Pubmed accepted abbreviation): Br J Sports Med
Page numbers: 530-532
Summary of background and research design
This article provides a brief review on the background and efficacy of four sports nutrition supplements: glycine, histidine-containing dipeptides, inosine, and β-hydroxymethylbutyrate (HMB).
Summary of research findings
Glycine - the smallest amino acid; non-essential (synthesized from serine), present in most proteins and highly concentrated in collagen. No purported benefit in and of itself, although combination of glycine with other nutrients has been studied. In limited studies, glycine-proprionyl-L-carnitine (GPLC) may decrease oxidative stress and/or enhance vasodilation.
Histidine - when combined with β-alanine, forms carnosine, which has numerous functions, and apparently assists in pH buffering. Dietary carnosine and analogs (anserine, balenine) are consumed in the diet in meat, and affect intramuscular carnosine synthesis by elevating blood β-alanine concentrations. Supplementation with 4-6 g/day of β-alanine for 4-10 weeks effectively augments muscle carnosine levels, and in some studies has improved exercise performance (delay time to exhaustion in high-intensity cycling). This effect is not dependent on ingested histidine.
Inosine - a nucleoside involved in oxygen transport by stimulating red blood cell concentrations of 2,3-diphopshoglycerate (2,3-DPG). It has been proposed to enhance exercise performance by improving oxygen transport and/or elevating ATP concentration, although there is no research to support either assertion.
HMB - a metabolic product of the essential branched chain amino acid leucine, approximately 5% of oxidized leucine becomes HMB. It may indirectly inhibit degradation of muscle protein, and supplementation of 1.5-3.0 g / day has elicited trends for improved strength and muscle growth. Recent reviews suggest these benefits are relatively small for trained males, but greater in the untrained or elderly.
Interpretation of findings/Key practice applications
Glycine - no benefit; GPLC may provide limited benefit, although research is scant
Histidine - no benefit by itself. Histidine-containing dipeptides such as carnosine may improve resistance to fatigue in high intensity exercise by elevating intramuscular carnosine, however dietary β-alanine, not histidine, is the key determinant of intramuscular carnosine synthesis.
Inosine - no established benefit
HMB - may provide some benefit on strength and muscle growth, particularly with increasing age or among untrained individuals. For those already engaged in regular exercise (esp. resistance training), a stronger benefit may be achieved with HMB and coingestion of nutrients that stimulate muscle protein anabolism (e.g. protein, essential amino acids, leucine)