Food intolerances can be confused for genuine food allergies, leaving people avoiding foods unnecessarily. 

Kimberly Holland
January 22, 2019
Arisara Tongdonnoi / EyeEm/Getty Images

A new study finds that nearly one in 10 American adults—or 26 million people—has at least one food allergy. But nearly double that amount, 19 percent of adults, thinks they do.

Researchers from Northwestern University surveyed more than 40,000 American adults. Almost one in five people from those they surveyed said they had a food allergy.

But when the researchers posed a series of questions designed to suss out true food allergies from other types of reactions, they found that only half of self-reported food allergies were legitimate.

The study, which was published earlier this month in JAMA Network Open, suggests that many Americans suppose a negative reaction to a food is an allergy, and they self-restrict themselves from the food in order to prevent a future reaction.

In reality, what they may have experienced is a food intolerance, something that can certainly be uncomfortable, but it is not life-threatening like a true food allergy can be.

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Food Intolerance vs Food Allergy

A food intolerance, according to the American Academy of Allergy, Asthma, and Immunology (AAAAI), is the result of enzyme deficiencies in your gastrointestinal (GI) system. Without specific enzymes, your body cannot properly break down certain foods.

Take for example a milk intolerance, also known as lactose intolerance. You likely know someone who must take an over-the-counter enzyme before they can scoop into ice cream or sip on a milkshake. That’s because their GI system doesn’t have the enzymes it needs to break down lactase, the natural sugars in dairy.

If they don’t take the enzyme, they may experience uncomfortable stomach symptoms, including bloating and diarrhea. They will not, however, face a life-threatening reaction.

A food allergy, on the other hand, is the result of an immune system overreaction. If you’re allergic to a food, your body reads proteins from the offending food as a dangerous intruder. It sends out a protein called Immunoglobulin E (IgE) to attack and destroy the invading protein. 

What it’s actually attacking, however, is a harmless food. This response can cause hives, itching, swelling, and watery eyes. It can also cause severe symptoms like swelling in the throat, sudden drops in blood pressure, and anaphylaxis. This reaction can be life-threatening if it’s not treated with an epinephrine injection quickly.

Differentiating between a true food allergy and a food-related gastrointestinal issue can be difficult without a doctor.

“There are so many adults out there who have a negative reaction to a food. It is really important to get a proper diagnosis so that they can really know is this something treatable like lactose intolerance, or is this a life-threatening food allergy that they need to be very careful with,” Ruchi Gupta, a professor of pediatrics at Northwestern University and a co-author of the research told The Guardian

Most Common Food Allergies

The researchers found the most common food allergy is shellfish. Nearly three percent of American adults, or 7.2 million people, are allergic to shrimp, lobster, crab, mussels, oysters, and other mollusks and crustaceans.

Milk, peanuts, tree nuts, fin fish, egg, wheat, soy, and sesame round out the remaining top food allergies.

Researchers were surprised to find that nearly half of people in the survey developed at least one food allergy during adulthood. Certain food allergies (shellfish and fin fish) are more likely to develop in adulthood, the researchers write. That suggests new food allergies among adults may be increasing, though it’s not clear why.

Less than half (48 percent) of all the study participants who reported convincing symptoms of at least one food allergy had a formal diagnosis from a doctor. People who had a life-threatening reaction were more likely to see a doctor. Indeed, 38 percent of people in the survey had an allergic response that required a previous emergency department visit.

Even those who were diagnosed were not always taking all the vital steps to protect themselves from a possible future reaction. The study shows that only 65 percent of people who had gone to a hospital because of an allergic reaction were carrying an epinephrine autoinjector, the medicine that could save their life in the event of a future severe reaction.

When You Should See a Doctor

What this study finds is that many people have a bad reaction to food and assign the term “allergy” to it, when in fact it may be an intolerance. After all, it’s simple enough to dismiss symptoms as an allergy and carry on while avoiding those foods.

However, many people may be needlessly avoiding food when they don’t have to. Some food intolerances can be treated if they’re properly diagnosed.

If you think you have a food allergy or intolerance, talk with your doctor. Explain what you experience when you eat the food. Keep a food diary if the symptoms are chronic or happen frequently. A food diary can help you and your doctor spot possible offending foods.

Your doctor may also refer you to an allergist, a specialist who can test for and diagnose food allergies and intolerances. Most health insurance plans will cover this visit and test.

If you discover you have a true food allergy, your doctor can walk you through steps you need to take to avoid the food and prescribe potentially life-saving medicine.

If the results of the study do not show an allergy, you and your doctor can talk about other issues that might be causing you discomfort and unwanted symptoms.