L-alanyl-L-glutamine (Sustamine™) is the combination of glutamine and alanine. Glutamine supplementation alone has shown to enhance fluid and electrolyte (liquid or gel that contains ions) absorption [1,2] but gives inconsistent effects  probably due to stability issues of glutamine in the gut. However, when glutamine is combined with alanine the ability to enhance electrolyte and fluid absorption appears to be greater than glutamine alone . Furthermore, the alanine-glutamine dipeptide appear to have greater stability at a low pH .
Dehydration can play a critical role in the outcome of a contest. For instance, it has been shown that with hypohydration levels of only 2% basketball players experience a significant performance decrement. At moderate levels of dehydration (4% body mass loss) significant alterations in afferent neural processing can occur .
Jay R Hoffman et al.  examined the efficacy of L-alanyl-L-glutamine (AG) ingestion on basketball performance, including jump power, reaction time, shooting accuracy and fatigue. Ten women participated in four trials (40-min basketball game each). During the first trial (DHY) subjects were not allowed to rehydrate. During the second trial (W) subjects consumed only water and during the other two they consumed either low dose (1 g per 500 ml – AGL) or higher dose (2 g per 500 ml – AGH) of L-alanyl-L-glutamine concentration. A 12.5% (p = 0.016) difference in basketball shooting performance was noted between DHY and AGL and an 11.1% (p = 0.029) difference was seen between AGL and W. Compared to DHY, visual reaction time was significantly greater following AGL (p = 0.014). Differences (p = 0.045) in fatigue were seen only between AGH and DHY. No differences were seen in peak or mean vertical jump power during any trial.
Rehydrating with L-alanyl-L-glutamine during the rest breaks of the game may have contributed to a more efficient fluid and electrolyte uptake, minimizing the destructive effects of dehydration .
Silva, Alessandra C., et al. “Efficacy of a glutamine-based oral rehydration solution on the electrolyte and water absorption in a rabbit model of secretory diarrhea induced by cholera toxin.” Journal of pediatric gastroenterology and nutrition 26.5 (1998): 513-519.
van Loon, Frederik PL, et al. “The effect of L-glutamine on salt and water absorption: a jejunal perfusion study in cholera in humans.” European journal of Gastroenterology & Hepatotogy 8.5 (1996).
Li, Yousheng, et al. “The effect of glutamine-supplemented total parenteral nutrition on nutrition and intestinal absorptive function in a rat model.” Pediatric surgery international 22.6 (2006): 508-513.
Lima, Aldo AM, et al. “Effects of an alanyl-glutamine—based oral rehydration and nutrition therapy solution on electrolyte and water absorption in a rat model of secretory diarrhea induced by cholera toxin.” Nutrition 18.6 (2002): 458-462.
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- Dougherty, Kelly A., et al. “Two percent dehydration impairs and six percent carbohydrate drink improves boys basketball skills.” Medicine and science in sports and exercise 38.9 (2006): 1650.
Montain, Scott J. Montain SJ, and William J. Tharion WJ Tharion. “Hypohydration and muscular fatigue of the thumb alter median nerve somatosensory evoked potentials.” Applied Physiology, Nutrition, and Metabolism 35.4 (2010): 456-463.
Hoffman, Jay R., et al. “L-alanyl-L-glutamine ingestion maintains performance during a competitive basketball game.” Journal of the International Society of Sports Nutrition 9.1 (2012): 4.