Identifying and Understanding Food Allergies and Intolerances

A food allergy is an abnormal response of the immune system. When you eat something you are allergic to, your body sends out antibodies that react with the substance you are allergic to, which causes symptoms like itching, hives, rashes, and GI upset.

Food intolerance is caused by the body's inability to digest a particular food or a chemical in that food.

A true food allergy elicits an immune system response, and some of the symptoms can be life-threatening. Symptoms of a food allergy can include itchy skin or a rash, hives, and wheezing, as well as gastrointestinal symptoms like nausea or diarrhea. In some cases, the response of the immune system can be fast and intense, leading to anaphylactic shock.

A food intolerance, on the other hand, has milder symptoms and only affects the gastrointestinal system.

An allergic reaction can be life-threatening. Signs of a severe allergic reaction include trouble breathing, flushing of the skin, feeling faint, itching on the palms and soles, rapid heart rate, low blood pressure, and loss of consciousness. An anaphylactic reaction is a medical emergency.

Severe allergic reactions are treated with epinephrine, and many people who know they have severe food allergies carry epinephrine with them in case of an emergency. While food intolerance may cause abdominal discomfort, the symptoms are not nearly as severe as those of food allergies.

The nine most common food allergens are milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and sesame.

Symptoms are generally the same no matter what the allergen is: hives, flushed skin, swelling in the face or mouth, wheezing, swelling of the throat, abdominal cramping, diarrhea, and vomiting.

A food allergy can be triggered when a person eats, touches, or inhales a protein in food  that they have antibodies against. Some people can react when they touch or breathe in foods they are allergic to; even eating the smallest amount can lead to a significant reaction.

Exposure can also occur in other ways, for example, through cross-contamination or food processing. The allergen may not be listed as an ingredient, but if the food was in the same facility or prepared in the same kitchen as the allergen, there is a chance that someone can still have an allergic reaction.

Avoiding allergens is critical to avoid an anaphylactic reaction. To avoid exposure, read the ingredient labels at least twice to ensure you do not accidentally eat something you are allergic to. Some packages will have a warning label clearly stating what allergens the product contains or if the product is processed in facilities with an allergen.

If you're going out to eat, speak to the restaurant beforehand to ensure they can accommodate your needs. Stick with simple dishes with limited ingredients, and avoid desserts as they often contain allergens.

Signs of a food intolerance usually appear a few hours after eating the food or ingredient that is causing it. The most common symptoms include bloating, passing gas, abdominal pain, or diarrhea, but some people may also experience rashes, fatigue, headache, or joint pain. Symptoms can last hours to days.

There are several ways to check for food intolerance. A doctor may recommend an elimination diet, where you stop eating certain foods and then add them back into your diet one at a time until your symptoms return to pinpoint what is causing the intolerance. Doctors can also use blood tests to determine food sensitivities or a breath test to check for lactose or fructose intolerance.

Research on the effectiveness of blood testing for food intolerances is somewhat limited, but some studies show that it can be beneficial for people with irritable bowel syndrome.

Multiple studies found that an elimination diet based on food antibodies found through blood testing was more effective for controlling mixed IBS than a low FODMAP diet, which eliminated foods with certain types of sugars.

Sesame was added to the list of common allegens that must be identified on food labels. Research shows that sesame allergies have grown rapidly. Researchers have yet to identify the precise reason, but it may be because of the increased use of soy around the work.

Adults may develop allergies due to pollen food allergy syndrome, which occurs when someone has a sensitivity to a specific type of pollen and then eats a fruit or vegetable that has a similar protein structure to the allergen.

For example, someone allergic to ragweed pollen may develop an allergy to melons, bananas, zucchini, or cucumbers, while someone allergic to grass pollen may develop an allergy to tomatoes, oranges, or celery. New onset food allergies in adulthood may also be caused by infections, changes in the environment, and hormonal shifts.

To manage emerging allergies, figure out what you are allergic to. A doctor can perform allergy testing, or you can try to determine what you may be allergic to by keeping track of your exposures and your symptoms. Steroid nasal sprays and antihistamines can help control seasonal allergies, or you can talk to your doctor about allergy shots to desensitize your body to an allergen.

Histamine intolerance is a sensitivity to dietary histamine. The body cannot break down histamine, so it accumulates, leading to many possible symptoms, including bloating, diarrhea, headache, nasal congestion, itching, rashes, or hives.

Some foods that contain histamine or cause your body to release histamine include alcohol, cheeses, pork, chocolate, nuts, egg whites, and processed meats. Histamine intolerance can be mistaken for a food allergy, but your doctor can do tests to determine the cause of your symptoms.

Histamine intolerance is believed to be caused by a deficiency of an enzyme called diamine oxidase (DAO) in the GI tract. This deficiency can affect the body's ability to degrade histamine in foods. Many things can lead to a DAO deficiency, including genetics, liver and kidney diseases, age, medications, and conditions that affect the gut.

The most common strategy for managing histamine intolerance is a low histamine diet. Generally, this diet involves avoiding foods high in histamine, like cured meats, fermented foods, processed seafood, shellfish, alcohol, chocolate, nuts, and soy. For people with a confined histamine intolerance, it can be beneficial to work with a nutritionist to learn more about what to eat and what to avoid.