DEAR DOCTOR K: What is the difference between a food allergy and a food intolerance?
DEAR READER: They both involve food, but other than that, food allergies and food intolerances have little in common.
Food allergies are orchestrated by the body’s immune system. Food intolerance results from the gut’s inability to digest food normally. Food allergies can be fatal; food intolerance causes discomfort but is not usually serious.
Food allergies require eliminating all traces of the food from your diet. Food intolerances can be managed without such drastic measures.
A food allergy is the immune system’s overreaction to a normally harmless food. The most common foods that people are allergic to are milk, eggs, peanuts, tree nuts, fish, shellfish, wheat and soy.
When someone with a food allergy eats an offending food, the immune system springs into action. An antibody called IgE signals immune cells to release chemicals that stimulate nerves, dilate blood vessels and cause inflammation. This can cause lightheadedness; itching, hives or rash; swelling of the lips, tongue and throat; and nausea, vomiting, cramping and diarrhea.
Rarely, a food allergy will trigger a life-threatening, whole-body reaction known as anaphylaxis. That’s one of the reasons that some airlines no longer hand out peanuts on flights. People with food allergies must completely avoid the dietary culprit.
Food intolerance results from the body’s inability to properly digest or metabolize a food. Symptoms include gas, bloating, nausea and diarrhea. Lactose, a milk sugar, and gluten, a protein in grains, are the substances that people are most likely to be intolerant or sensitive to. Intolerance to lactose leads to cramping pain in the abdomen and loose bowel movements.
The reaction to gluten can range from mild to severe. With severe intolerance, the intestines produce so much uncontrollable diarrhea that a person can suffer from severe dehydration.
One common and effective way to reduce symptoms is enzyme supplementation. Say you’re lactose intolerant. This means you don’t produce enough lactase, the enzyme that breaks down lactose, or milk sugar, into smaller, more easily digestible molecules. Taking a supplement that contains lactase can help.
Probiotics might also help. There’s some evidence that ingesting “gut-friendly” bacteria may help relieve lactose intolerance. However, there’s no standard formulation for probiotics, and finding one that’s right for you can be a hit-or-miss affair.
There is no similar antidote to gluten. A person with gluten intolerance needs to avoid any foods that contain gluten. Better labeling of gluten on food packages and the creation of more gluten-free products in recent years has made life somewhat better for gluten-intolerant people.
Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.