What is food intolerance?

People have a food intolerance when they have difficulty digesting certain foods and have an unpleasant physical reaction when they eat those foods.

Food intolerances and food allergies are caused by different biological processes and are diagnosed and treated differently. The problem in food intolerance lies in the digestive system, not in the immune system as in food allergies, though the symptoms of the two types of food reactions can be similar.

Causes of food intolerance

Food intolerance may be caused by:

• Lack of an enzyme needed to digest a certain food, or insufficient enzymes to digest a food fully. Examples include:
  • Lactose intolerance, which is caused by the absence of an enzyme needed to digest milk and other dairy products
  • The gas buildup experienced after eating foods like beans, lentils, cabbage or apples
  • Gluten intolerance that is not celiac disease, which can cause uncomfortable reactions after eating food made with wheat, rye or barley
  • Fructose intolerance, an inability to fully absorb this sugar compound, which is found naturally in fruits and vegetables and is added to foods and drinks as a sweetener
• Sensitivity to certain chemicals in food. This can include sensitivity to chemicals that occur naturally in food or to chemical food additives. Examples include:
  • Monosodium glutamate (MSG), which is sometimes added to food to enhance flavor but also occurs naturally in such foods as parmesan cheese, tomatoes and soy sauce. Whether added or naturally occurring, MSG can cause unpleasant reactions in some people.
  • Salicylates are natural chemicals that are produced by plants as a defense against insects and disease, and are found in fruits, vegetables, teas, coffee, nuts, spices and honey. They can cause reactions ranging from a stuffy nose to asthma and hives in people who are intolerant.
  • Amines, which are produced by bacteria in food during storage or fermentation. Amines are found in bananas, pineapples, avocados, citrus fruits, chocolate, cured meat, smoked fish, aged cheese and wine. In people who are amine intolerant, eating these foods can cause flushed skin, migraines, stuffy nose, diarrhea and other reactions.
  • Caffeine, which is found in coffee, tea, soda and energy drinks. Caffeine can cause anxiety, rapid heartbeat, restlessness or insomnia in people who are hypersensitive to the chemical, even after consuming only small amounts.
  • Sulfites, chemicals added to foods and drinks as preservatives. People who are sensitive to sulfites can react with flushed skin, hives, stuffy nose, diarrhea, coughing or wheezing. Sulfite sensitivity is sometimes seen in people with asthma.
• Irritable bowel syndrome (IBS). This chronic condition causes annoying and often painful abdominal and bowel symptoms, sometimes in reaction to eating particular foods. People with IBS are more likely to have digestive problems after eating and may be more sensitive to discomfort caused by gas and the movement of food through the digestive system.
• Psychological factors. For some people, certain foods can cause nausea and other digestive problems for psychological reasons. Even the thought of the food can make a person sick if this is the cause.

Signs and symptoms of food intolerance

Symptoms of food intolerance vary by individual, the type of food that causes the reaction, and the amount of the food eaten. Problematic food eaten in small amounts may cause no symptoms, while larger portions may cause great discomfort. Symptoms may include:

• Nausea
• Stomach pain or cramps
• Gas or bloating
• Vomiting
• Heartburn or acid reflux
• Diarrhea
• Constipation
• Headaches, migraines
• Skin rash or flushed skin
• Hives
• Fatigue
• Irritability or nervousness (from caffeine intolerance)
• Anemia

Testing and diagnosis for food intolerance

Unlike food allergies, which can be diagnosed relatively quickly by an allergist with a patient history combined with blood and skin-prick tests, food intolerances are identified through trial and error or by using a food elimination diet with breath tests to look for carbohydrate malabsorption.

If your child has a reaction to a particular food, especially if it is an immediate reaction, they should be seen by an allergist to understand whether the cause is a food allergy. If a food allergy is ruled out as the cause of the reaction, a GI specialist or an integrative medical team with a nutritionist will use the trial-and-error method or an elimination diet to understand if the problem is caused by food intolerance.

In the trial-and-error method, your child may be asked to keep a food diary, recording what they eat and the timing of any symptoms. By looking back at what your child ate in the hours before symptoms are noted in the log, the medical team can help find the foods that are causing problems.

In the elimination diet, your child will completely eliminate all of the foods suspected of causing problems, then add them back into their diet slowly, one at a time. It is important to work with your child’s healthcare provider or a registered dietitian when starting an elimination diet to make sure your child is completely avoiding the appropriate food components, and your child's nutritional needs are being met.