Do You Have a Food Allergy or Just an Intolerance—How To Tell

If your tummy feels crummy after most meals and snacks, you may have a food allergy, intolerance or a sensitivity. Here’s how to figure out what’s causing your digestive distress.

By Michele Shapiro

If you’re feeling bloated or nauseated more often than not these days, a food sensitivity or intolerance could be to blame.

“You can develop food sensitivities and intolerances, as well as food allergies, as you age,” says Jenn LaVardera, M.S., R.D., a dietitian based in Southampton, NY.  LaVardera estimates that 2 to 4 percent of adults have food allergies, while 6 percent have food intolerances. “Many people claim to have allergies when they actually have sensitivities,” she says. To learn why sometimes even some healthy foods aren’t loving you back, the first step is learning the difference between allergies, intolerances and sensitivities.

Food allergies

Allergic responses come on suddenly and tend to be severe—even life-threatening, says LaVardera. Your immune system mistakes something in a particular food, be it shellfish, nuts, eggs, gluten or something else, as harmful and attacks it. In addition to stomach-related symptoms, an allergic reaction can trigger a rash, hives or itchy skin, shortness of breath or, in the worst-case scenario, trouble swallowing or breathing. “If you suspect that you have a food allergy, visit an allergist [an M.D. who specializes in identifying allergens], who’ll do a blood test and rule things out,” suggests LaVardera.


“With an intolerance, you just don’t feel well after eating the food,” says LaVardera. It usually comes on gradually and isn’t life-threatening. An intolerance means you don’t have the enzyme to digest a certain compound in the food. The most common intolerance is to lactose, a sugar found in dairy products such as milk.

Food sensitivities are similar to intolerances, but harder to nail down. A person may have a negative reaction to a certain food sometimes, but it might not always be the same reaction, and it might not happen every time the person eats the food. “More research is needed into what causes sensitivities,” LaVardera says.

How to identify the culprit

You should consult a registered dietitian, who can help you pinpoint what’s causing a food intolerance or sensitivity. An R.D. can guide you through an elimination diet that lasts for four to six weeks on average. “The first step is to cut out processed foods,” LaVardera says. “There are so many ingredients hidden inside them [that could trigger a reaction]. If you have a gluten sensitivity, for instance, you need to eliminate things you may not even think of, like soy sauce and beer.” So an expert’s supervision is advisable; the other key is keeping a detailed food journal.

“For the first two or three weeks, clients eat a basic diet of fruit, lean protein (no shellfish), rice milk and fats like olive oil; vegetables are allowed (though you may want to limit cruciferous vegetables like broccoli to reduce bloating). Some grains, such as rice and quinoa, are also allowed.”

Then you start adding foods back one at a time. For instance, you’ll add in shellfish for a few days and see if you have a reaction. If not, you can incorporate that food into your diet. Next, you’ll add another food, such as nuts, for a few days and see if you’re your body reacts. “Food sensitivities can take two or three days to show up,” she says.

Alcohol and coffee are verboten throughout the elimination process, since they can wreak havoc with your gut.

As challenging as the elimination process may sound, it can help pinpoint any foods that are causing you gastric distress, and that will make you feel more at ease for the remainder of swimsuit season—and beyond.