What Is a Food Allergy?
A food allergy is an immune system response. It occurs when the body mistakes an ingredient in food -- usually a protein -- as harmful and creates a defense system (antibodies) to fight it. Food allergy symptoms develop when the antibodies are battling the "invading" food. The most common food allergies are peanuts, tree nuts (such as walnuts, pecans and almonds), fish, and shellfish, milk, eggs, soy products, and wheat.
What Is Food Intolerance?
Food intolerance is a digestive system response rather than an immune system response. It occurs when something in a food irritates a person's digestive system or when a person is unable to properly digest or breakdown, the food. Intolerance to lactose, which is found in milk and other dairy products, is the most common food intolerance.
What Are the Symptoms of a Food Allergy?
Symptoms of a food allergy can range from mild to severe, and the amount of food necessary to trigger a reaction varies from person to person. Symptoms of a food allergy may include:
- Rash or hives
- Nausea
- Stomach pain
- Diarrhea
- Itchy skin
- Shortness of breath
- Chest pain
- Swelling of the airways to the lungs
- Anaphylaxis
Symptoms of food intolerance include:
- Nausea
- Stomach pain
- Gas, cramps, or bloating
- Vomiting
- Heartburn
- Diarrhea
- Headaches
- Irritability or nervousness
How Common Are Food Allergies and Intolerances?
Food allergies affect about 4% of teens and adults and 5% of children. Food intolerances are much more common. In fact, nearly everyone at one time has had an unpleasant reaction to something they ate. Some people have specific food intolerances. Lactose intolerance, the most common food intolerance, affects about 10% of Americans.
What Causes Food Allergies and Intolerances?
Food allergies arise from sensitivity to chemical compounds (proteins) in food. They develop after you are exposed to a food protein that your body thinks is harmful. The first time you eat the food containing the protein, your immune system responds by creating specific disease-fighting antibodies (called immunoglobulin E or IgE). When you eat the food again, it triggers the release of IgE antibodies and other chemicals, including histamine, in an effort to expel the protein "invader" from your body. Histamine is a powerful chemical that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system.
As a result of this response, food allergy symptoms occur. The allergy symptoms you have depend on where in the body the histamine is released. If it is released in the ears, nose, and throat, you may have an itchy nose and mouth, or trouble breathing or swallowing. If histamine is released in the skin, you may develop hives or a rash. If histamine is released in the gastrointestinal tract, you likely will develop stomach pains, cramps, or diarrhea. Many people experience a combination of symptoms as the food is eaten and digested.
Food allergies often run in families, suggesting that the condition can be inherited.
There are many factors that may contribute to food intolerance. In some cases, as with lactose intolerance, the person lacks the chemicals, called enzymes, necessary to properly digest certain proteins found in food. Also common are intolerances to some chemical ingredients added to food to provide color, enhance taste, and protect against the growth of bacteria. These ingredients include various dyes and monosodium glutamate (MSG), a flavor enhancer.
Substances called sulfites are also a source of intolerance for some people. They may occur naturally, as in red wines or may be added to prevent the growth of mold.
Salicylates are a group of plant chemicals found naturally in many fruits, vegetables, nuts, coffee, juices, beer, and wine. Aspirin also is a compound of the salicylate family. Foods containing salicylates may trigger allergy symptoms in people who are sensitive to aspirin. Of course, any food consumed in excessive quantities can cause digestive symptoms.
How Can You Tell the Difference Between a Food Allergy and Intolerance?
Food allergies can be triggered by even a small amount of the food and occur every time the food is consumed. People with food allergies are generally advised to avoid the offending foods completely. On the other hand, food intolerances often are dose related.
People with food intolerance may not have symptoms unless they eat a large portion of the food or eat the food frequently. For example, a person with lactose intolerance may be able to drink milk in coffee or a single glass of milk, but becomes sick if he or she drinks several glasses of milk.
Food allergies and intolerances also are different from food poisoning, which generally results from spoiled or tainted food and affects more than one person eating the food. Your health care provider can help determine if you have an food allergy or intolerance, and establish a plan to help control your symptoms.
How Are Food Intolerances Diagnosed?
Most food intolerances are found through trial and error to determine which food or foods cause symptoms. You may be asked to keep a food diary to record what you eat and when you get symptoms, and then look for common factors.
Another way to identify problem foods is to go on an elimination diet. This involves completely eliminating any suspect foods from your diet until you are symptom-free. You then begin to reintroduce the foods, one at a time. This can help you pinpoint which foods cause symptoms. Seek the advice of your health care provider or a registered dietitian before beginning an elimination diet to be sure your diet provides adequate nutrition.
How Are Food Intolerances Treated?
Treatment for a food intolerance is based on avoiding or reducing your intake of problem foods and treating symptoms when they arise.
Can Food Intolerances Be Prevented?
Taking a few simple steps can help you prevent the symptoms associated with food intolerance.
Learn which foods in which amounts cause you to have symptoms and limit your intake to amounts you can handle.
When you dine out, ask your server about how your meal will be prepared. Some meals may contain foods you cannot tolerate and that may not be evident from the description on the menu.
Learn to read food labels and check the ingredients for problem foods. Don't forget to check condiments and seasonings. They may contain MSG or another additive that can lead to symptoms.
