Performance
IgG food sensitivity tests do not identify what is making athletes sick
By John Hyland, . Life and Health Today.
Home blood tests that claim to identify food sensitivities are a fixture of athlete life, but the immunoglobulin G (IgG) antibody they measure, a protein the immune system produces in response to things it has encountered, rises when a food has been eaten and tolerated, not when it causes harm. That is the finding MySportScience reported in a review of the evidence on food reactions in athletes.
The gap between belief and biology is striking. A systematic review of European studies, cited by MySportScience, found that roughly one person in six reported having had a food allergy at some point, while only about one person in a hundred actually reacted when a food was given under controlled challenge conditions.
Much of the gap comes down to how common gut symptoms are in the general population, and how naturally the mind connects a bad afternoon to the last meal. Certain carbohydrates found in wheat, onions, legumes and some fruits pass through the small intestine without being absorbed and are then fermented in the large intestine, producing gas and discomfort.
Expectation makes things worse. In a double-blind crossover study of 37 people with irritable bowel syndrome who believed they reacted to gluten, reported by MySportScience, symptoms improved on a diet low in these fermentable carbohydrates. A gluten-specific effect was found in only 8 percent of participants. Once a person is convinced a food is the problem, eating it can produce symptoms regardless of what it actually contains. Researchers call this the nocebo effect, and a test report naming specific foods provides exactly the kind of conviction that triggers it.
For athletes specifically, MySportScience notes that gut symptoms during training are common and are usually linked to reduced blood flow to the gut during exercise, mechanical factors, or the timing and composition of food around sessions, rather than to food allergy.
Two dietary approaches are popular among athletes. A short trial of a low-FODMAP diet, meaning one that restricts the fermentable carbohydrates described above, reduced daily gut symptoms compared with a high-FODMAP diet in a small, single-blind study of 11 recreationally competitive runners over six days, according to MySportScience. Symptoms during the running sessions themselves did not differ between the two diets. The study was small and short, so the finding supports a targeted trial, not a permanent restriction.
A gluten-free diet is a different matter. In a double-blind crossover study of 13 competitive endurance cyclists without coeliac disease, seven days without gluten produced no difference in time-trial performance, gut symptoms, perceived wellbeing, or markers of intestinal damage and inflammation compared with seven days that included food bars providing 16 grams of wheat gluten daily, MySportScience reported. For athletes without coeliac disease, removing gluten has no demonstrated benefit in the evidence reviewed.
There is one condition where food and exercise interact in a medically serious way. In wheat-dependent exercise-induced anaphylaxis, a genuine IgE-mediated wheat allergy where IgE is the antibody responsible for true allergic reactions, symptoms appear only when wheat is eaten alongside a trigger such as exercise, non-steroidal anti-inflammatory drugs or alcohol. The same meal without the trigger is tolerated. Symptoms can range from hives to severe anaphylaxis. MySportScience notes that this condition is diagnosed by an allergist using history, IgE testing and skin tests, and that an IgG panel would show nothing useful, which illustrates why systemic symptoms linked to eating before exercise need a medical referral rather than a home test.
MySportScience recommends starting with the symptoms rather than the test result, using a food and symptom diary over two to three weeks, and ruling out training-related causes first. If a specific food remains a plausible suspect, removing one food or food group for two to four weeks and then deliberately reintroducing it, ideally with a sports dietitian, is the suggested approach. Removing several foods at once makes the result uninterpretable and raises the risk of nutritional shortfalls.
Certain symptoms call for a medical referral without waiting: reactions appearing within minutes to two hours of a meal, any sign involving the skin, airways or circulation, symptoms tied specifically to eating before exercise, blood in the stool, unexplained weight loss, iron deficiency or diarrhoea that does not resolve. If coeliac disease is being considered, gluten must stay in the diet until all testing is finished, since the relevant diagnostic tests only return valid results when the person is still consuming it.
What this evidence does not settle is whether longer or more carefully controlled trials of low-FODMAP eating would show a benefit during exercise itself, not just at rest. The runner study was six days long and involved eleven people. That is a starting point, not a conclusion.
Source: https://www.mysportscience.com/post/do-you-have-a-food-allergy-or-intolerance
Life & Health Today provides information for educational purposes only, not medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.