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Food intolerances

Allergy or Intolerance?

a glass of milk and soybeans

Food allergies and intolerance are often confused, although they are very different. To understand the types of reactions your body has to certain foods, here are some clarifications.

A food allergy is a sensitivity caused by an immune system response to a particular protein, an allergen, found in a food. Peanuts and nuts are very common examples. An allergy causes an immediate and short-term reaction.

A food intolerance is not an allergy. It is a reaction your digestive system has when you eat a certain type of food, and it does not cause immediate symptoms or damage to your intestines. In addition, the severity of your reaction depends on the amount of food you eat.

If you suffer an intolerance to a particular food, it is because your body does not produce the enzyme required to metabolize it, or it is more sensitive to an additive or chemical contained in the food. Intolerance to a food can begin at a young age, causing subtle symptoms that worsen later, as you age.

Examples of food Intolerances

Lactose Intolerance

Your digestive system does not produce enough lactase (enzyme), so your body cannot break down lactose, a sugar found in milk.

Gluten Sensitivity

You experience symptoms similar to those associated with celiac disease when eating wheat or other foods that contain gluten, but your blood tests do not reveal any disease-related abnormalities, and there is no sign of damage to your intestines.

Sensitivity to Food Additives

When you eat foods that contain, for example, sulphites (additives found in wine, dried fruit and canned foods), you experience itching, redness, respiratory problems and headaches.

It is also important not to confuse susceptibility to non-celiac gluten (SGNC), or gluten intolerance, with celiac disease, which is not a food intolerance but an abnormal immune system response to gluten.

Causes and Symptoms

In general, symptoms of food intolerance occur several hours after a food is consumed and are often linked to your digestive system. You may experience abdominal cramps, diarrhea, vomiting, flatulence, a sense of bloating, itching or headache.

The causes of food intolerance may vary and are related to several factors:

  • Absence of an enzyme that facilitates the digestion of a food (e.g. milk intolerance)
  • Irritable bowel syndrome
  • Sensitivity to food additives (e.g., sulphites, dyes, monosodium glutamate)
  • Stress or psychological factors
  • Genetic factors
  • Certain medications
  • Alcohol use
  • Environmental factors


With the exception of testing for lactose intolerance, there is no reliable and accurate medical test that can diagnose food intolerances.

Diagnosis of Lactose Intolerance

Hydrogen Test

The hydrogen test consists of evaluating, after a period of fasting, the presence of hydrogen in the air that you exhale before and within hours of consuming a specified amount of lactose. Undigested lactose in the intestine (caused by a deficiency in the lactase enzyme) turns into hydrogen and passes through your blood circulation, reaches the respiratory tract and is then exhaled. High levels of hydrogen in exhaled air indicate an anomaly in your lactose digestion.

Lactose Tolerance Test

The lactose tolerance test determines the level of glucose in your blood after consuming a certain amount of lactose. If you have a lactose intolerance, glucose does not increase because you have a lactase deficiency.

Genetic Testing

Genetic testing detects lactose intolerance associated with primary lactase deficiency. It involves analyzing your DNA to determine if you are predisposed to being lactose intolerant. This test can be done with a simple collection of cells from the inside of your cheek (with a swab). However, this test cannot diagnose secondary lactase deficiency that occurs after infection, inflammatory bowel disease or intestinal parasitosis.

The best way to identify other foods that may cause your symptoms related to intolerance is to keep a food journal. You record the foods you eat every day for a period of two to three weeks. If a food causes specific symptoms, you can eliminate it for a few days and reintroduce it into your diet and record your reaction.

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Living with a Food Intolerance

There is currently no medical treatment for food intolerance. To avoid symptoms, you must identify the foods that cause a reaction and avoid consuming them or consume them in small amounts.

Here are some helpful tips.

Modify your meals – Your intolerance may be caused by the cumulative effect of combining certain foods during a meal. For example, if you experience symptoms after eating a pizza, you may be able to tolerate the tomatoes and cheese when eaten alone, but not when you combine them. By eliminating one ingredient at a time, you can determine which food combinations affect you most.

Change your servings – If you decrease the portion of the food that causes digestive problems, you can also decrease the symptoms it causes.

Find a substitute – If the food you need to remove from your diet is an important nutritional source, find an appropriate substitute. If you have to cut out foods that contain gluten, you may be depriving yourself of fibre and B vitamins. You can compensate by eating, for example, gluten-free bread, or grains such as rice, quinoa or buckwheat. If you are lactose intolerant, take a lactase supplement to help you digest dairy products, drink milk without lactose, or almond or coconut milk to ensure a diet high in protein and calcium.

To learn more about food intolerance:

Food Allergy Canada

Harvard Medical School

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