Food intolerance vs food allergy: what's the difference?

A food intolerance and food allergy can occasionally bring on similar symptoms, so people often confuse the two. However, there are significant differences: While eating something you are intolerant to can cause discomfort, eating a food you are allergic to can have life-threatening consequences.

In this article, renowned London-based gastroenterologist Dr Michael Mendall guides us through the main differences between food intolerance and a food allergy.

What is the difference between a food allergy and food intolerance?

A true food allergy causes an atopic immune system reaction and can involve numerous organs in the body. Usually, those with a food allergy are allergic to a particular ingredient found in food that brings out an allergic reaction. It can be very severe and sometimes, life-threatening in some instances.

A food intolerance, on the other hand, isn’t as serious and typically limited to digestive symptoms. The reaction is not immune-mediated; instead, the intolerance is due to the direct physical effects of a particular food or gut bacteria.

Furthermore, someone with a food allergy, for example to peanuts, will always need to avoid that particular food completely to prevent a serious allergic reaction occurring. In contrast, those with a food intolerance may well be able to consume small amounts of the offending food and, in some cases, even prevent a reaction occurring. For example, someone with lactose intolerance may be able to drink small amounts of milk but not be able to handle large quantities.

Are the symptoms of food intolerance and food allergy different?

A food intolerance means your body cannot properly digest certain foods or a particular food irritates the digestive system, so the symptoms are usually limited to the gastrointestinal system. Symptoms of food intolerance can include:

• nausea and/or vomiting
• excessive gas
• abdominal pain and/or cramping
• diarrhoea
• irritability
• headaches

Symptoms of a food allergy are different and much more serious. The body's immune system sees the troublesome food as an invader which brings about an allergic reaction; meaning chemicals such as histamine are released in the body. Symptoms include:

• breathing problems and/or wheezing
• throat tightness, which can lead to anaphylaxis
• swelling around the face
• tingling or itching around the mouth
• coughing
• vomiting
• abdominal pain
• rash, also known as hives or urticaria
• drop in blood pressure

What are some common food intolerances?

A British study was carried out, of more than 10,000 patients, and found the foods most often associated with intolerances were:

• wheat
• milk
• beans
• onions and garlic
• cabbage
• coffee
• fatty or deep fried foods

What are common food allergies?

Foods that most commonly cause an allergic reaction are:

• cow’s milk
• eggs
• tree nuts, which include brazil nuts, almonds, cashews, pine nuts etc.
• peanuts
• fish and shellfish
• wheat
• soy
• some fruit and vegetables

What causes food intolerance?

It’s not completely clear why a person may be sensitive to certain foods. It can sometimes be caused by genetic factors, meaning it’s just the way they were born and lack the necessary enzymes to break down particular foods properly.

For example, lactose intolerance is particularly widespread worldwide with 65% of the human population being lactose intolerant. Across Northern Europe, however, intolerance levels in countries such as Finland and Sweden are much higher at around 80%. Research suggests that over centuries people in this area of the world have slowly lost the ability to digest lactose due to a variety of factors.

Can you get over a food intolerance?

Yes, it is possible to reverse a food intolerance - but not a food allergy. To get over an intolerance there are very specific approaches to take which may well be different for each individual.

Some people often find that certain life changes can bring on an intolerance. Stress can make the gut hyperactive and cause a temporary intolerance to certain food groups. You may find that once that person is able to manage their stress, they will gradually be able to tolerate that food again.

Likewise, women’s food intolerances can change during pregnancy. Their symptoms may well improve (or worsen) which is typically due to the change in hormone levels in the body.

Are there tests for food allergies and intolerances?

For food allergies, there are some tests:

• Skin-prick test — this test is the most reliable in which drops of food extracts are placed on the patient’s arm. If itching, swelling and redness occur, it usually indicates a positive reaction. There is a chance this test brings about a severe reaction known as anaphylaxis, so it is always carried out where there are facilities to manage and treat this if it happens.
• A blood test — this is an alternative to a skin-prick test. It measures the number of allergic antibodies in the blood.
• Food elimination test — the offending food is eliminated from the diet for around two weeks and then reintroduced. If the symptoms return when the food is reintroduced, it suggests a food allergy. You shouldn’t attempt this test yourself without talking to a doctor beforehand.

For food intolerances, there may be some tests but most are unreliable. The gold standard for identifying a food intolerance is to eliminate the offending food from the diet for a couple of weeks and then reintroducing it slowly to determine your reaction. Again, you shouldn’t attempt this test yourself without talking to a doctor beforehand.

How can food allergies and intolerances be managed?

Food allergy

The only way to manage a food allergy is to avoid it and eliminate it from your diet completely. This is very important as those who have a food allergy can break out into a severe allergic reaction even from tiny trace amounts. If you think you have an allergy to a certain food, you should completely avoid it and visit a medical specialist as soon as possible.

Food intolerance

The best way to manage a food intolerance is to make changes to your diet, this includes eliminating it completely. Sometimes, medications can help people to tolerate their intolerances. For example, if diarrhoea is a symptom, the patient can take antidiarrheal or antispasmodic drugs which can help relieve them of this.

If you believe you have either a food allergy or intolerance and would like to see a specialist, visit Dr Michael Mendall’s Top Doctors profile and check his availability.