Do you have a food allergy or intolerance? What athletes need to know

Athletes are regularly offered home blood tests that promise to identify the foods behind their bloating, fatigue or poor recovery, and many coaches and practitioners have met an athlete who arrives with a report listing foods to avoid. In a companion blog we explain what these tests measure, why a raised immunoglobulin G (IgG) against a food shows that the food has been eaten and tolerated rather than that it causes problems, and what the professional allergy organisations say about them. But the athlete who bought the test usually has real symptoms, and dismissing the test does not make those symptoms go away. In this blog we will explore four questions. Why do so many people believe they react to food? If the foods on the report are not the cause, what is? When is a food genuinely the problem? And what should a coach or practitioner do instead?

Why do so many people believe they react to food?

The market for these tests exists because many more people believe they react to food than can be shown to do so. In a systematic review of European studies, 17.3% of people reported having had a food allergy at some point in their lives and 5.9% reported a current one (1) (see the graphic above). Sensitisation, meaning that the immune system recognises a food protein, was found in 10.1% with specific IgE tests and 2.7% with skin prick tests. But only 0.9% actually reacted when the food was given in a food challenge. In other words, about one person in six believes they have had a food allergy, and about one in a hundred has one that can be demonstrated. That leaves a large number of people with real symptoms and no explanation.

Part of this gap is explained by how common gut symptoms are. Bloating, abdominal discomfort and loose stools occur regularly in the general population, they come and go, and most people eat several times a day, so a bad day is easily linked to the last meal, and the occasions that seem to confirm the link are the ones that are remembered. Some foods do cause symptoms, but not through the immune system: lactose causes symptoms in people with low lactase activity, and some carbohydrates in foods such as wheat, onions, legumes and some fruits are poorly absorbed and fermented in the large intestine.

Expectation adds to this. In a double-blind crossover study, 37 people with irritable bowel syndrome who believed they were sensitive to gluten first followed a diet low in these fermentable carbohydrates, and their symptoms improved (2). When gluten was added back their symptoms worsened, but they worsened to a similar degree when whey protein was added instead, and a gluten-specific effect was found in only 8% of participants. Once a person is convinced that a food causes problems, eating it can produce symptoms and avoiding it can bring relief, regardless of what the food contains. This is known as the nocebo effect, and a test report that names the foods provides exactly that conviction.

Can a change in diet help?

If a food group does play a role, the practical question is whether removing it reduces symptoms. Two diets are popular among athletes: a diet low in fermentable carbohydrates (FODMAPs, short for fermentable oligosaccharides, disaccharides, monosaccharides and polyols) and a gluten-free diet. Some symptioms occur at rest and some symptoms may be exercise induced (and made worse by foods).

In 11 recreationally competitive runners with a history of gut symptoms during exercise, 6 days on a low-FODMAP diet reduced daily gut symptoms compared with 6 days on a high-FODMAP diet, with less flatulence, urge to defecate, loose stools and diarrhoea (4). Symptoms during the running sessions themselves did not differ between the diets. This was a small, short, single-blind study, so the reasonable conclusion is that a short, targeted reduction in FODMAPs is worth trying in an athlete with symptoms, not that FODMAPs should be restricted permanently.

Gluten is a different story. In 13 competitive endurance cyclists without coeliac disease, 7 days of a gluten-free diet was compared with 7 days of the same diet plus food bars providing 16 g of wheat gluten per day, in a double-blind crossover design (5). There was no difference in 15-minute time trial performance, in gut symptoms during or outside exercise, in perceived wellbeing, or in markers of intestinal damage and inflammation. For athletes without coeliac disease, removing gluten therefore has no demonstrated benefit, and it makes eating while travelling and racing considerably more difficult.

For athletes without coeliac disease, removing gluten therefore has no demonstrated benefit

When food and exercise really do interact

There is one condition in which a food causes symptoms only in combination with exercise. In wheat-dependent exercise-induced anaphylaxis (WDEIA), a wheat allergy mediated by immunoglobulin E (IgE), the antibody responsible for food allergy, symptoms occur only when wheat is eaten together with a cofactor such as exercise, NSAIDs or alcohol (6). The same meal without the cofactor is tolerated. Symptoms range from intermittent hives to severe anaphylaxis. The diagnosis is made by an allergist, based on the history, IgE testing (usually against a component of gluten called omega-5 gliadin), skin tests and, where necessary, a challenge with the cofactor present. A completely wheat-free diet appears to promote tolerance less than continued regular consumption of gluten-containing cereals in the absence of cofactors, and every patient should carry an adrenaline autoinjector (6). An athlete with WDEIA would find nothing useful on an IgG panel, which is a clear illustration of why symptoms that are systemic and linked to exercise after eating need a medical referral rather than another test kit.

So and IgG test does not work, but what should I do?

The conversation goes better if it starts with the symptoms rather than with the test. The athlete paid for the test because something is wrong, and dismissing the test can sound like dismissing the problem. It helps to explain what the test measured and to ask the athlete to compare the list with their own diet, because the overlap with the foods they eat most is usually obvious.The next step is a food and symptom diary for two to three weeks, recording what was eaten, how much, how long before training, the type and intensity of the session, the conditions and any medication.

The next step is a food and symptom diary for two to three weeks, recording what was eaten, how much, how long before training, the type and intensity of the session, the conditions and any medication. Training-related causes should be checked first, because they are the most common: hydration, the concentration of carbohydrate drinks, the timing and composition of the pre-exercise meal, fibre and fat close to sessions, NSAID use and heat. A food becomes a plausible cause only if the same symptom follows it repeatedly in comparable circumstances. If so, one food or food group can be removed for two to four weeks, ideally with a sports dietitian, and then deliberately reintroduced. Removing several foods at once makes the result impossible to interpret and increases the risk of nutritional shortfalls.

Some situations need a medical referral straight away: reactions within minutes to two hours of eating, any involvement of the skin, airways or circulation, symptoms that occur only when exercising after eating, blood in the stool, unexplained weight loss, iron deficiency or persistent diarrhoea. If coeliac disease is suspected, gluten must not be removed before testing, because the tests are only valid while the athlete is still eating gluten.

Practical takeaways

• About one person in six believes they have had a food allergy, whereas about one in a hundred reacts in a food challenge. Common gut symptoms, carbohydrates that are poorly absorbed, and expectation (the nocebo effect) explain much of this gap.

• Gut symptoms affect 30 to 50% of athletes and are usually caused by reduced blood flow to the gut, mechanical factors or nutrition around training, not by food allergy.

• A short, targeted low-FODMAP diet reduced daily gut symptoms in one small study in runners. A gluten-free diet had no benefit in cyclists without coeliac disease.

• Start with the symptoms, a food and symptom diary and the training-related causes, test one change at a time, and refer immediately when there are red flags such as rapid, systemic or exercise-dependent reactions.

References

1. Nwaru BI, Hickstein L, Panesar SS, Muraro A, Werfel T, Cardona V, Dubois AEJ, Halken S, Hoffmann-Sommergruber K, Poulsen LK, Roberts G, Van Ree R, Vlieg-Boerstra BJ, Sheikh A. The epidemiology of food allergy in Europe: a systematic review and meta-analysis. Allergy 69(1) 62-75, 2014.

2. Biesiekierski JR, Peters SL, Newnham ED, Rosella O, Muir JG, Gibson PR. No effects of gluten in patients with self-reported non-celiac gluten sensitivity after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates. Gastroenterology 145(2) 320-328, 2013.

3. de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med 44(Suppl 1) S79-S85, 2014.

4. Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK. Low FODMAP: a preliminary strategy to reduce gastrointestinal distress in athletes. Med Sci Sports Exerc 50(1) 116-123, 2018.

5. Lis D, Stellingwerff T, Kitic CM, Ahuja KDK, Fell J. No effects of a short-term gluten-free diet on performance in nonceliac athletes. Med Sci Sports Exerc 47(12) 2563-2570, 2015.

6. Faihs V, Kugler C, Schmalhofer V, Scherf KA, Lexhaller B, Mortz CG, Bindslev-Jensen C, Biedermann T, Brockow K. Wheat-dependent exercise-induced anaphylaxis: subtypes, diagnosis, and management. J Dtsch Dermatol Ges 21(10) 1131-1135, 2023.