Glutamine and Sport: Athlete Immunity, Athlete's Gut, What the Studies Show

From an Oxford study published in 1996. Its reasoning: endurance athletes have more infections after prolonged exercise, plasma glutamine drops after this type of effort, and immune cells use it as fuel. The team gave 151 athletes, after a marathon, ultramarathon or intensive rowing training, a glutamine drink or placebo immediately after exercise and two hours later, then a questionnaire about infections in the following seven days: 81% without infection on glutamine versus 49% on placebo. A striking result, based on self-reported infections, which launched twenty years of research.

No. A crossover, randomized, double-blind trial from the Muscle Research Centre in Copenhagen had ten athletes cycle for two hours at 75% of their VO2 max, with glutamine or placebo during and after exercise, and directly measured their immune cells. Glutamine did prevent the drop in plasma levels, but it had no effect on lymphocyte traffic, NK cell activity, T cell proliferation, or hormones. The authors conclude that the study does not support a mechanistic role for glutamine in exercise-induced immune changes.

Because they don't measure the same thing. The Oxford study counts infections reported by questionnaire, without biological measurement. The Copenhagen trial directly measures immune cell function, double-blind. Michael Gleeson's review explains the key: glutamine is indeed essential for lymphocyte proliferation, but its concentration doesn't drop enough after exercise to compromise it. The supposed mechanism therefore doesn't exist, which makes the 1996 result difficult to explain otherwise than by its methodological limitations.

Yes, and it's recent: the intestine during exercise. A trial from John Moores University in Liverpool had ten men run for one hour at 70% of their VO2 max in a 30-degree chamber, after a placebo or 0.25, 0.5 or 0.9 g of glutamine per kilo of lean mass, taken two hours before. Intestinal permeability, measured by the lactulose to rhamnose ratio, was lower under glutamine at all doses, and very likely lower at the highest dose, in a dose-dependent manner. Digestive symptoms, mild in this trial, did not change. The authors conclude that athletes competing in heat could benefit from an acute dose before exercise to preserve intestinal integrity.

High doses: 0.25 to 0.9 g per kilo of lean mass, meaning for a 60 kg lean mass runner between 15 and 54 g in a single dose, two hours before exercise. The effect was already present at the lowest dose and increased with dose. This is a ten-person trial, under laboratory conditions, which requires confirmation; but it provides a clear order of magnitude, which is that of clinical nutrition and not that of a teaspoon.

The Loughborough review is clear on this point too: the reasons given for supplementation, immune support, glycogen synthesis, anticatabolic effect, have received little support from well-controlled studies in healthy, well-nourished adults. Our dedicated article on glutamine and recovery reviews the trials, dose by dose.

In healthy adults, single doses of 20 to 30 g have no notable adverse effects, and 28 g per day for 14 days caused no damage in athletes, according to the reference review. Doses up to 0.65 g per kilo have been tolerated without abnormal ammonia elevation. The limit is elsewhere: in case of kidney or liver failure or serious illness, glutamine is decided with a doctor, as detailed in our guide on glutamine and the intestine.

That the 1996 immune hypothesis did not withstand mechanistic trials or reference review: glutamine does not protect athletic immunity. That its emerging area is the intestine during heat exercise, where a trial shows reduced permeability in a dose-dependent manner at 0.25 to 0.9 g per kilo of lean mass two hours before. That muscle recovery has no solid data. And that the doses from positive trials are counted in tens of grams, in a single dose before exercise.