Klein, J., Nyhan, W. L., & Kern, M. (2006). The effects of alanine supplementation on plasma amino acid concentrations, fuel substrates, and endurance. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1998.

This study examined the influence of alanine on plasma concentrations of amino acids and fuel substrates as well as exercise performance. In a double blind design, four different solutions (6% alanine (ALA); 6% sucrose (CHO); 6% sucrose and 6% alanine (ALA-CHO); or an artificially sweetened placebo (PLC) were randomly tested during separate trials. During each trial, trained cyclists (N = 10) ingested 500 ml of the test solution 30 minutes before an exercise bout and 250 ml after 15, 30, and 45 minutes of exercise. Participants cycled for 45 min at 75% of VO2max after a 5-minute warm-up. Following the 45-minute exercise, a 15-minute trial of accumulated work was used to assess performance. Blood samples were collected before the initial beverage consumption and immediately before the 15-min accumulated-work trial.

Plasma concentration of alanine increased significantly during every trial but much more (approximately 10-fold) when alanine was supplemented compared with less than 2-fold increases when either CHO or PLC were consumed. Alanine ingestion, with or without sucrose, increased plasma concentrations of glutamine, aspartate, glutamate acid plus asparagine, glycine, threonine, serine, and proline, while it decreased phenylalanine concentration. Plasma leucine and isoleucine concentrations decreased significantly during the ALA, ALA-CHO, and PLC trials, but not significantly during the CHO trial. Serum free fatty acid concentrations were higher at the end of exercise for PLC compared to the other conditions. Plasma glucose concentrations were higher post-exercise for the CHO versus the PLC trial and remained stable during ALA and ALA-CHO trials. Serum insulin concentration increased for CHO, remained unchanged for ALA-CHO, and decreased for ALA and PLC trials. No differences in work completed during the performance bouts were observed among the trials. Ratings of gastrointestinal discomfort at the end of exercise were similar among trials.

Implication. Alanine supplementation produced potentially favorable effects on plasma concentrations of most gluconeogenic amino acids but failed to alter performance at the end of one hour of exercise.

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