Food Intolerence vs Food Allergy

Harvard Health Letters
Premium Health News Service

Walk down the aisles of your local supermarket, and you'll see something you likely wouldn't have encountered a decade ago--shelves devoted entirely to gluten-free cereals, breads, muffins and other foods. Restaurants have also jumped on the bandwagon, revising their menus to include dishes without gluten, a protein found in wheat.

The gluten-free diet was designed for people with celiac disease, who can't tolerate any foods containing gluten because their immune system reacts to it and damages the small intestine in response. Celiac disease is a very real, very uncomfortable, and potentially very serious condition. Left untreated, it can lead to anemia, osteoporosis, and intestinal cancers.

About 1 percent of Americans, or 3 million people, have true celiac disease. Another 6 percent, or 18 million people, are sensitive to gluten. Eating gluten-containing foods doesn't damage their intestines, but it can still produce gastrointestinal discomfort, along with symptoms like headaches and fatigue.

People in a third group are allergic to wheat. When they're exposed, they get more traditional allergy symptoms, which can range from tingling around the mouth to hives, throat swelling, and difficulty breathing.

"It's confusing that people can have all these different reactions to the same food," says Dr. Ciaran Kelly, professor of medicine at Harvard Medical School and medical director of the Celiac Center at Beth Israel Deaconess Medical Center, Boston, Mass. "It's important to make the distinction between food allergies and intolerance, because there is a lot of confusion and there are differences in treatments.


When you're intolerant of a particular food, it's usually because your body lacks an enzyme needed to break down a component in that food (such as lactose, the sugar in milk). Or, your body might be sensitive to a particular chemical or additive in the food. The process leading to food intolerance often starts early in life, but symptoms can be too subtle to notice at first.

Examples of food intolerance:    1. Lactose intolerance. Your body can't break down the sugar lactose because your gut contains reduced levels of the intestinal enzyme lactase. Lactose is found in dairy foods such as milk or ice cream. When you eat these foods, you can develop uncomfortable gastrointestinal symptoms like gas and diarrhea.

2. Gluten sensitivity. You have many of the same symptoms as someone with celiac disease after eating wheat or other foods containing gluten (stomach pains, bloating, fatigue), but your immune system doesn't produce the blood test abnormalities seen in people with celiac disease, and there is no evidence of damage in the intestines.

3. Sensitivity to food additives. You get symptoms like flushed skin and wheezing from eating additives such as sulfites (found in wine, dried fruits and canned goods), or headaches, palpitations, or numbness after eating foods flavored with monosodium glutamate (MSG).

Symptoms of food intolerance:

You may be able to eat small amounts of the food without having any reaction to it. Your symptoms will come on gradually after you've eaten a particular food.

Often, those symptoms will involve your digestive system--such as nausea, gas, or diarrhea. Your reaction will be uncomfortable, but it's usually not life-threatening.



A true food allergy involves your immune system. Your body recognizes a normally innocuous food, such as peanuts or milk, as a potentially harmful foreign invader. It goes into defensive mode, producing high levels of an antibody called immunoglobulin E (IgE). Often food allergies start when you're young, but it's not impossible for them to appear for the first time later in life, Dr. Kelly says.

Examples of foods that commonly cause allergic reactions include eggs, fish and shellfish, milk, peanuts, soy, tree nuts (hazelnuts, walnuts, almonds), and wheat.

Symptoms of a food allergy:  1. You could have a reaction from eating just a tiny amount of the food, or simply from being around the food.

2. You can experience allergic symptoms such as hives, swelling, and itchiness, as well as gastrointestinal symptoms such as abdominal pain, vomiting and diarrhea.

3. If your allergy is severe, you might have an anaphylactic reaction, which can begin with a rash, swelling of the tongue and throat, trouble breathing, dizziness, or fainting. It can be life-threatening.


Don't shortchange your diet

Avoid foods that bother you, but don't do a full-scale purge of your diet without good cause (for example, celiac disease or true food allergies). Because of the abundance of gluten-free foods available, many Americans have begun to think that all wheat and other grain products are bad for them.

"There's a way of thinking that gluten is an unhealthy food," Dr. Kelly says. "Somehow, if a food is gluten-free, it's considered healthier, and there's little basis for that."

Cutting out foods like wheat, barley, and rye can rob your diet of nutrients such as fiber, calcium, and B vitamins. Going gluten-free could have a similar effect on your purse. One Canadian study found that gluten-free foods cost 242 percent more than comparable regular foods. Work with a doctor or dietitian to create a diet that's safe for your system, while still healthy and well rounded. -- Harvard Women's Health Watch

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