How to Know for Certain You Can't Tolerate Certain Foods

Somewhere in between low-carb diets and juice cleanses, declaring a food intolerance became a trend. Maybe it's due to the growing awareness of food sensitivities, or perhaps it's related to people's attempts to explain their mysterious symptoms. Of course, food intolerances are very real, but it's becoming increasingly common to claim one without truly understanding what it entails.

A true food intolerance is when your digestive system has a hard time breaking down a certain food. In some cases, it can handle small amounts, but reacts adversely to larger servings. This may "be due to lack of certain enzymes, past medications or illness, or reactions to compounds within your food," says Katrina Trisko, M.S., R.D., C.D.N., a registered dietitian at Bethany Medical Clinic of New York.

Yet, identifying the culprit isn't always easy, especially if you've been eating the same foods for a long time. It also doesn't help that food intolerances (and their symptoms) can be elusive.

"When someone has a food intolerance, they may have a wide array of symptoms that don't necessarily point to the food they're eating," explains Amanda A. Kostro Miller, R.D., L.D.N., a registered dietitian who serves on the advisory board for Smart Healthy Living. For example, along with digestive upset, you may experience respiratory problems or acne. Even conditions like headaches, heartburn and chronic anxiety could be related to intolerances.

Think you can't tolerate a food? Instead of blindly omitting this and that from your dietary repertoire, here's what you can do to know for sure.

1. Keep a food log

"Keeping a food journal is one of the best ways to [determine] if you're sensitive to a food," shares Trisko. This practice involves a detailed, time-stamped record of your food intake and symptoms. By recording this information, you can identify patterns between what you're eating and how you're feeling.

Miller recommends logging your meals, drinks and snacks, along with their ingredients and portion sizes. When recording your symptoms, note the time and severity. She also suggests logging other stressors, like travel or poor sleep. This is useful in case you don't find a food-related pattern.

According to Trisko, it's best to keep a food log for about two weeks so you can observe your food reactions over time.

2. Eliminate possible culprits

"If you have a list of problematic foods, [start a basic] elimination diet to see if these foods are the culprit," says Miller. First, set a date to start eliminating the potentially distressing foods one at a time. Continue for four to eight weeks, then record how your symptoms change during this time. Your best bet is to work with a registered dietitian who can help you navigate the diet and interpret your results.

And if your symptoms don't improve? "You're either not completely eliminating your triggers—perhaps via hidden sources—or your issues may not be food-related," she says.

3. Reintroduce the foods

If you felt better during the elimination phase, you've likely omitted the problematic food. However, if you've removed multiple foods, you still need to determine which one is causing issues.

To do this, "choose one problematic food and record the date it was added," Miller explains. Keep eating the food a few times each week, for one to two weeks, noting any associated symptoms. Continue reintroducing other problematic foods, one by one, in the same manner. You're likely not intolerant to a food if it doesn't cause any problems, but if it does cause unpleasant symptoms, try limiting or avoiding it in the future and see how you feel.

If basic elimination doesn't give you answers, visit a gastroenterologist or dietitian. Even if you are successful in identifying the triggering food, it's still wise to consult a dietitian. They can educate you about substitutes to ensure you're getting enough nutrients, along with helping you understand how much of it you can eat without developing symptoms.

If you suspect a food allergy, see an allergist before experimenting with your diet. Unlike food intolerances, food allergies occur when your immune system overreacts to a substance, causing an allergic reaction that can be life-threatening.

Most importantly, listen to your body, and work with your doctor whenever possible. With time and patience, you can better understand your body and find relief.