You are currently viewing What is a food intolerance?

What is a food intolerance?

Nutrition allergy, also known as nutrition hypersensitivity induced by non-IgE, or non-allergic food hypersensitivity, refers to difficulty in digesting such foods. It is important to remember the distinction between food sensitivity and food allergy.

Food allergies activate the immune system, while resistance to food does not. Some people have digestive issues after eating such foods, but their immune system has not responded-there is no response to histamine.

Foods most commonly associated with food intolerance include dairy products, gluten-containing grains and foods that cause accumulation of intestinal gas, such as beans and cabbage.

Fast facts on food intolerance

Here are some key points about food intolerance. More detail and supporting information is in the main article.

  • Symptoms of food intolerance tend to take longer to appear than symptoms of allergies
  • The symptoms are varied and can include, migraine, cough, and stomachache
  • Some food intolerance is caused by the lack of a particular enzyme


Gluten free signs among bread
Gluten is one of the most common causes of food intolerance.

If the patient has a food deficiency or an allergy may be difficult to assess, as the signs and symptoms sometimes overlap.

According to James Li, M.D., Ph.D., an allergy specialist at the Mayo Clinic, only small quantities result in symptoms when it’s an allergy, which may be the case for peanuts. Though small quantities would typically have no impact with food intolerance.

Compared with food allergies, the signs of food intolerance typically take longer to develop.

Onset usually occurs several hours after the offending food or substance has been consumed, and can continue for several hours or days. For some cases it may take 48 hours for symptoms to appear.

Many individuals are intolerant to numerous food types, making it more difficult for doctors to decide if this may be a chronic illness or food intolerance. It may take a long time to find out which foods are the culprits.

The following are the most common symptoms of food intolerance, says the Australian NSW Food Authority:

  • Bloating
  • Migraines
  • Headaches
  • Cough
  • Runny nose
  • Feeling under the weather
  • Stomach ache
  • Irritable bowel
  • Hives


There can be many causes of food intolerance, and we will take a look at each of these in turn.

1) Absence of an enzyme

Enzymes are required to completely digest foods. When any of these enzymes are absent, or inadequate, it may hinder proper digestion.

Those that are intolerant of lactose do not have enough lactase, an enzyme that breaks down milk sugar (lactose) into smaller molecules which the body can then break down and absorb through the intestine. It can cause spasm, stomachache, bloating, diarrhea, and gas if lactose remains in the digestive tract.

Individuals with milk protein allergy have similar signs to those with lactose intolerance; this is why people with lactose intolerance are frequently misdiagnosed as allergic.

Researchers at Tacoma, WA’s Mary Bridge Children’s Hospital and Health Center found that intolerance to fructose is common in children with chronic or severe abdominal pain.

For proper digestion almost all foods need an enzyme. Enzyme shortages are a frequent cause of food allergy, the British Allergy Foundation reports.

2) Chemical causes of food intolerance

Some chemicals in foods and beverages can cause intolerance in some cheeses, including amines, and caffeine in coffee, tea, and chocolates. Some individuals are more sensitive than others to such chemicals.

3) Food poisoning – toxins

Some foods have naturally occurring chemicals that can induce diarrhea, nausea, and vomiting to have adverse effects on humans.

Undercooked beans have aflatoxins that can cause digestive issues particularly unpleasant. Completely cooked beans have no poison to them. Therefore, people might wonder why after one meal they respond to beans, and not after another.

4) Natural occurrence of histamine in some foods

Some foods, such as fish that has not been properly processed, may have histamine accumulation as they “red.” A number of people are especially susceptible to this natural histamine and develop skin rashes, stomach cramps, diarrhea, vomiting and nausea.

Often, the symptoms are similar to anaphylaxis (a strong allergic reaction).

5) Salicylates are present in many foods

Salicylate aversion, also known as the allergy of salicylate, happens when someone responds of regular quantities of salicylate ingested.

Salicylates are salicylic acid derivatives which occur naturally in plants as a mechanism of defense against harmful bacteria, fungi, insects and diseases.

Many foods contain the chemicals and most people will consume salicylate-containing foods without any harmful effects. Some individuals, however, suffer from symptoms after eating large amounts. Individuals intolerant to Salicylate should avoid high-level foods.

For most plant-sourced foods, salicylates are present like most fruits and vegetables, spices, herbs, tea, and flavor additives. Especially high levels of mint-flavouring, tomato sauce, berries and citrus fruit.

Foods processed with flavor additives are also typically high in salicylates.


Some common types of food intolerance are:

  • lactose
  • wheat
  • gluten
  • caffeine
  • histamine, present in mushrooms, pickles, and cured food
  • additives such as artificial sweetners, coloring, or other flavorings

While consuming bread, some people experience a reaction but this does not necessarily mean a gluten intolerance. Anyone who thinks that they may have a gluten allergy should see a doctor before giving up gluten, because cereals can be an essential source of different nutrients.

Food additives and intolerance

Proceed meat ball
Processed meat can contain nitrates that are the source of some people’s food intolerances.

Throughout the past thirty years, food additive intolerance has been a constantly growing concern, as more and more foods contain additives.

Even so, it is not known that food additive allergy affects more than 1 per cent of people.

Additives are used to improve flavors, make foods more appealing, and increase their shelf life. Examples of additives to foods include:

  • Antioxidants
  • Artificial colorings
  • Artificial flavorings
  • Emulsifiers
  • Flavor enhancers
  • Preservatives
  • Sweeteners

A relatively small number of the thousands of chemicals used in the food industry are believed to be causing problems. The following additives to food are known to cause adverse reactions in humans:

  • Nitrates – known to cause itching and skin rashes. Processed meats are generally high in nitrates and nitrites.
  • MSG (monosodium glutamate) – used as a flavor enhancer. Known to cause headaches.
  • Sulfites – used as a food preserver or enhancer. Commonly used in wines. In the United States and European Union, wines bottled after 1987 and 2005, respectively, must state on their labels if they contain sulfites at more than 10 parts per million. A German study found that about 7 percent of people have an intolerance to wine.
  • Some colorings – especially carmine (red) and annatto (yellow).


If someone has a food deficiency or an allergy is not easy to tell, as the signs and symptoms sometimes overlap. Some similarities in the symptoms can help a doctor distinguish between the two. Throughout the vast majority of cases, signs of food allergy take much longer to manifest than food allergies.

It is best for patients to keep a diary and write down which foods are consumed, what the symptoms were and when they started. The diary data will help a dietician or doctor determine which foods cause adverse reactions and what measures should be taken.

Skin prick tests are not 100 percent reliable.
Skin prick tests are not 100 percent reliable.

In addition to lactose intolerance and celiac disease, there is no accurate, effective, and validated food intolerance test. An exclusion diet, also known as an elimination or diagnostic diet, is the safest diagnostic tool.

Intolerance to eat foods frequently can cause adverse reactions to run into each other. If this happens, it’s hard to recognize which foods to blame for. There is a greater chance of being misdiagnosed with a medical disorder or disease.

Exclusion diets are particularly useful when it comes to isolating the food from the culprit.

In a standard diet for exclusion, the alleged food is excluded from the diet for a specified time, usually from 2 weeks and 2 months. If the adverse reactions resolve during this time, the suspect one is more likely to have been found. If it is then reintroduced, this can be further confirmed and symptoms return.

The doctor can prescribe a skin and/or blood test to rule out an allergy to the food:

  • 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.

The best current food allergy treatment is either to avoid such foods, or to consume them less frequently and in smaller quantities, as well as to take supplements that may improve digestion.


Many people find that they have no reaction when they consume it again if they remain off the same food for a while – this is known as tolerance. Maintaining tolerance is just a matter of understanding how long to abstain, and how much to eat at reintroduction.

The only way to assess this is by trial-and-error, as each person reacts differently.