How a Gluten-Free Diet Affects Athlete Performance

Two small athlete trials found no performance advantage from removing gluten in people without celiac disease. Their size and duration leave small or longer-term effects uncertain. For athletes with celiac disease, strict gluten avoidance is medical treatment. If wheat seems to trigger symptoms, identify the cause before removing a staple source of training carbohydrate.⁶⁷

01Four causes of gluten-related symptoms

Bloating on a long run, loose stools after a pasta dinner, and fatigue in a heavy block can all get blamed on gluten. At least four different problems can produce those complaints, and each one leads somewhere different.

Celiac disease is a permanent immune-mediated reaction to gluten from wheat, barley, and rye that injures the small intestine. The American College of Gastroenterology's 2023 guideline treats it as a multisystem disorder, confirms it with antibody testing and, in most adults, an intestinal biopsy, and names strict lifelong gluten avoidance as the treatment.¹

Wheat allergy is an IgE-mediated allergy to wheat proteins. Symptoms include hives, rash, stomach cramps, vomiting, sneezing, and asthma, and an allergist diagnoses it with skin-prick or blood IgE testing.² In wheat-dependent exercise-induced anaphylaxis, a person can eat wheat at rest without trouble and then react when exercise follows the meal. Omega-5 gliadin, a gluten protein, is one of the main allergens involved.³

Non-celiac gluten or wheat sensitivity describes recurring symptoms after wheat or related grains once celiac disease and wheat allergy have been ruled out. No validated biomarker confirms it. The gluten sensitivity glossary entry covers the diagnostic criteria and a structured elimination and re-challenge.

Exercise-associated gastrointestinal symptoms come from exercise itself. Reduced gut blood flow, mechanical jostling, heat, dehydration, and concentrated fuel during the session can all produce nausea, cramping, and urgency, whatever the athlete ate the night before.⁴

These categories can overlap in the same person. An athlete with celiac disease can still get race-day cramps from an overconcentrated bottle.

02Test before cutting gluten

Testing before you change your diet helps preserve diagnostic accuracy. NIDDK states that doctors don't recommend starting a gluten-free diet before diagnostic testing because the diet can affect test results.⁵ Celiac antibody levels depend on ongoing gluten exposure. An athlete who goes gluten-free for two months, feels better, and then asks for a blood test may get a result that can no longer answer the question.

That leaves an athlete with two unknowns. They don't know whether a crumb of cross-contact is harmful to them, and they don't know whether they need the monitoring that comes with celiac disease. The ACG guideline lists iron deficiency, unexplained weight loss, chronic diarrhea, and other autoimmune conditions among the reasons to test.¹ Starting a gluten-free diet before testing can make it harder to establish whether celiac disease contributed to low ferritin.

If you already stopped eating gluten and now want an answer, talk to the clinician who would order the test. Reintroducing gluten for testing has its own dose and timing requirements, and a clinician should set them.¹ Do not design a home gluten challenge to get yourself ready for a lab visit.

03Gluten-free performance trials

The performance evidence for athletes without celiac disease comes down to two small studies.

The first was a 2015 randomized, double-blind crossover trial from the University of Tasmania. Thirteen competitive cyclists, 8 men and 5 women, with no positive celiac screening and no history of irritable bowel syndrome, ate a gluten-free diet for seven days twice, separated by a ten-day washout. In one week they also ate food bars containing 16 g of wheat gluten a day, and in the other they ate identical gluten-free bars. After each week they rode 45 minutes at a steady effort and then a 15-minute time trial. Time-trial work was 245.4 kJ with gluten and 245.0 kJ without it. GI symptoms, daily well-being scores, a marker of intestinal injury, and inflammatory cytokines did not differ between diets.⁶

The blinding is what makes that study useful. Athletes who choose to go gluten-free know they have changed their diet, and expectation alone can shift how a session feels. Here the cyclists did not know which bars contained gluten. Seven days is still too short to say anything about a season, and 13 riders is too few to rule out a small effect.

The second study is a 2025 pilot from the University of Freiburg. Twenty healthy male non-professional endurance athletes were assigned to six weeks of either a gluten-free diet or a mixed diet, with both groups doing the same sprint interval training program. The design was an open-label, matched-group pilot. Only 6 of 10 athletes finished in the gluten-free group, compared with 9 of 10 in the mixed-diet group. Both groups improved how far they could run in 60 minutes, by a median of 0.76 km in the gluten-free group and 0.60 km in the mixed-diet group, and the difference between groups was not statistically significant. The authors credit the sprint training for the gains and note that the study had no non-training control group.⁷

The Freiburg gluten-free group did lose more weight, a median of 2.7 kg against 0.3 kg. That group started about 9 kg heavier and reported eating about 700 kcal less per day at baseline, and the authors acknowledge possible underreporting of intake. A difference in six men cannot tell you whether gluten, energy intake, food choices, or chance produced it. At the intervention assessment, median iodine and vitamin D intakes in the gluten-free group were below their Adequate Intake (AI) values. The study compared those intakes with the AI without inferring inadequacy. Two of the six participants remained below the Average Requirement (AR) for calcium.⁷

Neither study found a performance gain from removing gluten in athletes without celiac disease. Together they cover 28 athletes who finished, over seven days in one study and six weeks in the other. That is thin evidence, and it leaves the claim of an ergogenic edge with no controlled data behind it.

04Wheat symptoms can come from fructans

Wheat contains more than gluten. It is also a major source of fructans, a group of fermentable carbohydrates that pull water into the bowel and produce gas when gut bacteria ferment them. Remove wheat and you remove both.

A 2018 double-blind crossover trial in Oslo tested this directly in 59 people who were already following a self-started gluten-free diet and had celiac disease excluded. They were not athletes. Each person rotated through seven days of muesli bars containing gluten, fructans, or neither. Fructans produced higher overall symptom and bloating scores than gluten. Gluten produced scores no different from placebo.⁸ That result explains one plausible mechanism across a group of people. It cannot identify what triggers symptoms in any single athlete.

The 2025 Sports Dietitians Australia and Ultra Sports Science Foundation position statement on exercise-related gut problems reaches the same point from the sports side. Its gluten-free section says symptom improvements that non-celiac athletes report may come from the accompanying drop in FODMAPs, especially fructans and galacto-oligosaccharides, or from broader changes in eating habits. It concludes there is no evidence supporting a gluten-free diet in non-celiac athletes to prevent or manage exercise-induced gut damage or exercise-associated GI symptoms, and it grades that evidence as level III.⁴ A position statement summarizes existing studies, and the only athlete trial behind its gluten conclusion is the 13-cyclist study.

A good week without wheat does not prove gluten was the problem. The same week often removes beer, pastries, large restaurant meals, and high-FODMAP foods, and it may overlap with a lighter training load. If fermentable carbohydrates look like the pattern, the low FODMAP diet is a time-limited protocol with a reintroduction phase built to find which groups you actually react to.

05Training can trigger gut symptoms

Some athletes who suspect gluten notice symptoms mainly in long or hard sessions and rarely on rest days. That pattern points toward the session itself. Concentrated drinks, gels taken without enough water, a high-fiber breakfast too close to the start, heat, and dehydration all produce the cramping and urgency that get pinned on the previous night's pasta.

The position statement lists carbohydrate and protein intake, hydration before and during exercise, short-term FODMAP reduction, and gut training as the strategies with mostly consistent benefit for exercise-associated symptoms.⁴ Gut training for race nutrition covers how to build tolerance to race-level carbohydrate intake over several weeks. Start there if your symptoms track intensity, duration, and fueling rate more than they track what you ate.

06Keep carbohydrate high without gluten

Athletes who need to eat gluten-free face one main fueling risk. Bread, bagels, pasta, wraps, cereal, and many bars are some of the easiest high-carbohydrate foods to eat in volume, and removing them without planned replacements can quietly lower daily carbohydrate on the days training demands the most.

The 2016 joint position statement from the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine sets daily carbohydrate targets by training load, roughly 5 to 7 g/kg for moderate daily training, 6 to 10 g/kg for one to three hours of moderate to high intensity work, and 8 to 12 g/kg for very high loads.⁹ Those targets stay the same when gluten leaves the diet, so the replacement foods have to carry the full load. The complete guide to macronutrients covers how carbohydrate fits with protein and fat across a training week.

Plain rice, potatoes, bananas, and corn provide gluten-free carbohydrate. Added ingredients, preparation, and serving still need cross-contact checks for celiac disease.¹¹

Rice, potatoes, corn, quinoa, buckwheat, millet, bananas, and fruit juice contain no gluten in their plain form and supply dense carbohydrate. Oats need a separate check. Oats do not contain gluten, yet they are often contaminated with other cereals, and the NHS advises people with coeliac disease to avoid oats that are not labeled gluten-free. A very small number of people with coeliac disease also react to avenin, the protein in oats.¹⁰ NIDDK notes that most people with celiac disease can safely eat moderate amounts of oats.¹¹

For packaged foods in the United States, a voluntary gluten-free claim on an FDA-regulated food, including dietary supplements, means the food contains less than 20 parts per million of gluten. The FDA chose that threshold partly because methods could not reliably detect lower levels, so a labeled food can still contain trace gluten below 20 ppm.¹² UK law uses the same 20 ppm cutoff for foods labeled gluten-free.¹⁰ Other countries set their own rules.

Cross-contact happens when gluten-free foods are prepared together with gluten-containing foods or served with the same utensils.¹⁰ For athletes with celiac disease, that includes team meals, shared hotel buffets, and aid stations where volunteers use the same hands for sandwiches and potatoes. Bringing your own gluten-free race food gives you control over its ingredients and handling. Keep it separate from shared food and utensils.¹¹

07Replace fiber and iron

Whole-grain wheat, rye, and barley are everyday fiber sources for many athletes. NIDDK warns that a gluten-free diet may not provide enough fiber, iron, and calcium.¹¹ Many gluten-free breads and pastas are built on refined rice, corn, potato, or tapioca starch, which fuel training well and contribute less fiber.

Replace fiber on purpose with quinoa, buckwheat, brown rice, oats labeled gluten-free, legumes, potatoes with skins, fruit, vegetables, nuts, and seeds. Time the higher-fiber meals away from key sessions. For iron, pair gluten-free grains and legumes with meat, fish, or eggs, or with a vitamin C source at plant-based meals. Fatigue, pallor, or declining training quality have many causes, so discuss persistent symptoms and iron testing with a clinician instead of assuming low iron. In athletes with celiac disease, low iron can reflect the disease itself, so recurring deficiency after diagnosis is a reason to go back to the gastroenterologist.¹

08A gluten-free fueling day

Take a 70 kg cyclist with diagnosed celiac disease doing a three-hour ride on a day that calls for about 8.2 g/kg, or roughly 576 g of carbohydrate. The example uses weighed portions and a named gluten-free sports gel. Carbohydrate totals exclude the plain chicken and cod listed with meals.¹³

That lands near 8.2 g/kg with no bread, pasta, or wheat-based bars. The meals rely on familiar staples such as rice, potatoes, oats, fruit, and juice. The gel provides a specified, labeled option for the ride. For race week, the same logic scales up to the 10 to 12 g/kg loading targets in how to set up a race-week nutrition plan.

09Get help for persistent symptoms

Get medical input before you change your diet if you have suspected celiac disease, iron deficiency, unexplained weight loss, chronic diarrhea, or a family history of celiac disease. Hives, swelling, wheeze, or faintness after eating wheat, especially when exercise follows, call for an allergist. Blood in the stool, repeated vomiting, or symptoms that persist on rest days need medical evaluation before any elimination plan.

A sports dietitian is worth the appointment when symptoms persist despite reasonable fueling changes, when a diagnosis requires a gluten-free diet and training carbohydrate keeps falling short, or when the list of foods you avoid keeps growing. The 2016 joint position statement recommends that athletes see a registered dietitian for personalized nutrition plans.⁹ Restriction that keeps expanding without a diagnosis can leave energy intake short of training demands, which the same statement treats as a threat to both health and performance.⁹

Without a diagnosed gluten-related condition, start with fueling concentration, hydration, and tolerated portions before removing wheat. With celiac disease, choose gluten-free foods that meet your own training carbohydrate target and control cross-contact.⁴⁹¹¹