When your immune system mistakes a protein in a particular food (most commonly milk, eggs, fish, peanuts, shellfish, soy, tree nuts, and wheat) as harmful, it produces Immunoglobulin E (IgE) antibodies, which cause an allergic reaction in the form of digestive symptoms like nausea or diarrhea, itchiness, hives, trouble breathing, or even life-threatening anaphylaxis, explains Janna Tuck, M.D., an allergist in Sante Fe, New Mexico.
Intolerances and sensitivities (gluten and dairy are common ones) typically manifest in digestive issues. In some cases, sensitivities can happen when your digestive enzymes aren’t fully breaking down your food, explains Jennifer Broxterman, R.D., founder of Nutrition Rx in London, Ontario, Canada. Larger molecules can escape through gaps in your intestinal wall and cause irritation. And even though this type of reaction is generally less serious (read: non-life-threatening) compared to true food allergies, it’s more than simply bothersome or uncomfortable: “When you’re an athlete trying to compete at the highest level, eating a food you’re sensitive to will impact your ability to absorb nutrients, as well as your recovery,” adds Helen Kollias, Ph.D., the Toronto-based director of science at Precision Nutrition.
There are a few ways your doctor can confirm a true allergy including blood tests, skin-pricks, and food challenges, where you eat the food in his or her office and watch to see how you respond. However, false positives are unfortunately common, says Tuck. Cross-reactions can happen. For example, if you’re allergic to tree pollen, you might come up as positive for a tree nut allergy. An allergist can help you figure out exactly how at-risk you are of developing a true allergy if you haven’t already, and guide you as to whether or not you need to avoid the food.
Despite the growing number of companies that claim otherwise, there aren’t quick, reliable ways to test for sensitivity issues. Unlike traditional allergy panels, most sensitivity tests look at your levels of a different antibody, IgG. But, the experts consulted for this story say that tests for IgG aren’t actually useful, because IgG antibodies simply show that you’ve been exposed to a food, not that it causes you any harm.
Elimination diets involve removing foods from your daily intake, starting with the most common allergens, and then reintroducing them, to see which ones cause problems. If you’re having gut-related issues like bloating and nausea, difficulty sleeping, or even chronic congestion, or if you feel like you’re optimizing everything related to your workouts and still not recovering quickly, it may be worth cutting out gluten and dairy for a few weeks and seeing how you feel, says Kollias. You could also try doing a more extensive elimination diet, though experts recommend working with a dietician to make sure you don’t accidentally cause any nutrient deficiencies.
Per Broxterman: During exercise, your sympathetic nervous (fight or flight) system is activated, and your body redirects blood flow from your digestive system to your muscles. That’s not a problem if the majority of the time you’re in a parasympathetic (rest and digest) state. But when you combine hard workouts with stressful conditions—work stress, a long commute, family pressure—that put you in a sympathetic state too much of the time, your digestion may suffer and your gut may overreact to certain foods like gluten or dairy, she explains.
“I see huge differences in my food sensitivity clients when they sleep more and do activities to stimulate the parasympathetic system,” says Broxterman. That includes restorative exercise like yoga, hiking, and stretching, spending time in nature, and practicing mindfulness, meditation, and breathing drills. By helping you manage stress, these activities can help you heal your gut and therefore make you more able to tolerate foods you otherwise couldn’t, Broxterman explains. She adds that nourishing and rebuilding your gut microbiome by getting plenty of soluble fiber (found in items like bran, barley, seeds, beans, lentils, and peas) along with a quality probiotic supplement, can improve digestion and sensitivity symptoms.
The bottom line: If you’re experiencing symptoms of a food allergy or sensitivity, your best bet is to work with an allergist or registered dietician to optimize your course of action. If you just have an inkling that something is off and it could be diet-related (or just wonder if going gluten-free or dairy-free or something-free could help you perform better), you could try an elimination diet though again, doing it under the supervision of a pro is ideal to avoid risking the placebo effect coming into play. Making lifestyle changes to reduce stress could also be a game-changer for your digestion.