Physical reactions to certain foods are common, but most are caused by a food intolerance rather than a food allergy. A food intolerance can cause some of the same signs and symptoms as a food allergy, so people often confuse the two.

A true food allergy causes an immune system reaction that affects numerous organs in the body. It can cause a range of symptoms. In some cases, an allergic food reaction can be severe or life-threatening. In contrast, food intolerance symptoms are generally less serious and often limited to digestive problems.

If you have a food intolerance, you may be able to eat small amounts of the offending food without trouble. You may also be able to prevent a reaction. For example, if you have lactose intolerance, you may be able to drink lactose-free milk or take lactase enzyme pills (Lactaid) to aid digestion.

Causes of food intolerance include:

Absence of an enzyme needed to fully digest a food – Lactose intolerance is a common example.

Irritable bowel syndrome – This chronic condition can cause cramping, constipation and diarrhea.

Sensitivity to food additives – E.g. sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people.

Recurring stress or psychological factors – Sometimes the mere thought of a food may make you sick. The reason is not fully understood.

Celiac disease – Celiac disease has some features of a true food allergy because it involves the immune system. However, symptoms are mostly gastrointestinal, and people with celiac disease are not at risk of anaphylaxis. This chronic digestive condition is triggered by eating gluten, a protein found in wheat and other grains.

How common are food allergies and intolerances?

Food allergies affect about 1 percent of adults and 7 percent of children, although some children outgrow their allergies. 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 specific food intolerance, affects about 10 percent of Americans.

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, this can include:

• Rash or hives
• Nausea
• Cramping stomach pain
• Diarrhea
• Itchy skin
• Shortness of breath
• Chest pain
• Swelling of the airways to the lungs

Anaphylaxis is a very serious and potentially fatal allergic reaction that involves a sudden drop in blood pressure, loss of consciousness and body system failure.

What are the symptoms of food intolerance?

Symptoms of food intolerance tend to take longer to appear than symptoms of allergies

• Nausea
• Stomach pain
• Gas, cramps or bloating
• Vomiting
• Heartburn
• Diarrhea
• Headaches/Migraines
• Irritability or nervousness
• Bloating
• Cough
• Runny nose
• Feeling under the weather
• Irritable bowel

Diagnosis

It is not easy to determine whether somebody has a food intolerance or allergy because the signs and symptoms often overlap. Certain patterns in the symptoms can help a doctor distinguish between the two. In the vast majority of cases, food intolerance symptoms take much longer to appear than food allergies.

Patients are advised to keep a diary and write down which foods are eaten, what the symptoms were like, and when they appeared. The data in the diary can help a dietician or doctor identify which foods are causing adverse reactions, and what steps to take.

Skin prick tests are not 100 percent reliable.

Apart from lactose intolerance and celiac disease, there is no accurate, reliable, and validated test to identify food intolerance. The best diagnostic tool is an exclusion diet, also known as an elimination or diagnostic diet.

Intolerance to regularly-eaten foods may result in adverse reactions running into each other. When this occurs, it is difficult to identify which foods are to blame. There is a higher risk that a chronic condition or disease is erroneously diagnosed.

Exclusion diets are extremely useful in isolating the culprit foods.

In a typical exclusion diet, the suspected food is removed from the diet for a set period, usually between 2 weeks and 2 months. If during this period the adverse reactions resolve, it becomes more likely that the culprit has been found. This can be further confirmed if it is then reintroduced and symptoms return.

Tests

The doctor may recommend a skin test and/or a blood test to rule out a food allergy:

Skin prick test – this determines the patient’s reaction to a specific food. A small quantity of the suspected food is placed on the patient’s back or forearm. The skin is pricked with a needle, allowing some of its substance to penetrate below the skin surface. Allergic people will react with a raised bump. However, skin prick tests are not 100 percent reliable.

Blood test – this measures levels of IgE (immunoglobulin E) antibodies. These tests are not 100 percent reliable either. The presence of IgE antibodies may be a part of the normal human response and indicate tolerance, rather than an adverse reaction, according to a study published in CMAJ.

Improvement

The best current treatment for food intolerance is to either avoid certain foods or eat them less often and in smaller amounts, as well as taking supplements that may help digestion.

Some people find that if they stay off the specific food for a while, they have no reaction when eating it again – this is known as tolerance. Maintaining tolerance is often a question of knowing how long to abstain and how much of it to eat when it is being reintroduced.

As each person reacts differently, the only way to determine this is by trial-and-error.

Sources used:

https://my.clevelandclinic.org/health/diseases/10009-food-problems-is-it-an-allergy-or-intolerance https://www.mayoclinic.org/diseases-conditions/food-allergy/expert-answers/food-allergy/faq-20058538
https://www.medicalnewstoday.com/articles/263965.php