Gluten-Free Diet May Not Boost Athletic Performance

We’ve got good news and bad news. The bad news first: If you’re an athlete who doesn’t have celiac disease, eliminating gluten probably won’t help you clinch that PB. But the good news: Pizza!

Researchers at the University of Tasmania and the Canadian Sport Institute Pacific tracked 13 non-celiac competitive cyclists as they followed both a gluten-free and a gluten-containing diet. In a double-blind, randomised, crossover study, researchers found that there were no statistically significant differences in athletic performance, perceived GI distress, inflammatory markers, intestinal damage, or overall well being between those who ate a gluten-free diet and those who consumed gluten.

Dana Lis, Ph.D., R.D., was the lead researcher for the study, which is set to publish in the December 2015 issue of Medicine and Science in Sports and Exercise and was released ahead of publication online last week. She says that she and Trent Stellingwerff, Ph.D., a physiologist at the Canadian Sport Institute Pacific, originally devised the study after seeing the gluten-free trend catching on with elite athletes.

“All the sudden we had a ton of athletes going gluten-free,” she says. “We as researchers and nutritionists didn’t really have much of a evidence-base with which to recommend whether a gluten-free diet is appropriate for you if you’re not celiac or have any other clinical conditions requiring gluten avoidance. Feeling better is great, and I think even the placebo effect can go a long way. For me personally, I want more science than ‘feeling better.’”

Lis had 13 cyclists eat the same diet for two seven-day periods with a 10-day “washout” period in between. The only difference between the two seven-day periods was that during one of the weeks the athletes ate cereal bars containing gluten. During the other week, the athletes snacked on gluten-free bars. All the other food, which was cooked and supplied by Lis and her team, was identical. As a double-blind study, neither the researchers nor participants knew which cereal bars they were eating, and Lis says the two varieties were undistinguishable to test subjects.

Each day the athletes completed questionnaires on GI distress (both right after exercise and in daily life) and overall well being. On the last day of each seven-day trial, the cyclists completed a 45-minute steady-state ride at 70 percent of their max effort, and a 15-minute, all-out time trial. During the 10-day “washout period” athletes could eat and train however they wanted. When the seven-day trial began anew, they had to replicate the first week’s diet and training, but with the other cereal bar swapped in.

Beyond looking at perceived GI distress and performance, Lis incorporated the 45-minute sub-maximal ride because she wanted to test whether a gluten-free diet could reduce damage to the intestines and gut permeability. “We know from previous research that a 45-minute exercise bout at 70 percent of your watt max will induce intestine injury,” she says. “So we knew that if we simulated that environment and gluten made that worse or better, we’d be more likely to pick up a change.”

But the researchers didn’t get a change. There were two specific indicators for intestinal injury and increased inflammation that Lis and her colleagues were looking for, but blood samples taken post-exercise showed no difference between the subjects who ate gluten and those who did not.

So if nothing changed, why do so many athletes report feeling and performing better on a gluten-free diet? “I just think there are a lot of things that affect an athlete’s diet when they go gluten free,” Lis says. “They’re likely to pay more attention to what they’re eating, to eat less processed foods, and to eat more fruits and vegetables. So I just think there’s a lot of other things going on, not just the gluten itself.”

To be clear, this research was all done around non-celiac athletes, and participants also had no history of irritable bowel syndrome. Some of the participants had tried gluten-free diets in the past, but none had done so within six weeks of starting the trial.

Lis is also the first to admit that the study used a small sample size, but providing 13 athletes with two full weeks of meals is an expensive endeavor. One criticism she expects to hear is that the trial wasn’t long enough to allow changes in gut flora to happen. “That could possibly have an effect on symptoms,” she says. “People will definitely ask that question. But based on clinical research, people who tend to experience symptoms from gluten tend to experience them from a few hours to a few days after ingesting gluten. So, given the clinical basis, definitely this is long enough.”

Lis also adds that she’s not anti gluten-free diets. “That’s not the case at all, we’re just curious,” she says. “I think it’s great when athletes aim to optimise their diet for both health and performance and feeling better is good, too.” Just know that science may not back up the results you’re experiencing.

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