Food intolerance, also known as non-IgE mediated food hypersensitivity or non-allergic food hypersensitivity, refers to difficulty in digesting certain foods. It is important to note that food intolerance is different from food allergy.
Food allergy triggers the immune system, while food intolerance does not. Some people suffer digestive problems after eating certain foods even though their immune system has not reacted - there is no histamine response.
Foods most commonly associated with food intolerance include dairy products, grains that contain gluten, and foods that cause intestinal gas buildup, such as beans and cabbage.
Symptoms of food intolerance
It can be difficult to determine whether the patient has food intolerance or allergy, because often signs and symptoms overlap. When it is an allergy even small amounts result in symptoms, as may be the case with peanuts, according to James Li, M.D., Ph.D., Mayo Clinic allergy specialist.1
With food intolerance tiny amounts will usually have no effect. Doctors can also test for Immunoglobin E (IgE) antibodies.
A symptom is something the sufferer feels and describes, such as pain or discomfort, while a sign is something others can detect, such as a rash.
The symptoms of food intolerance generally take longer to emerge, compared to food allergies. Onset typically occurs several hours after ingesting the offending food or compound and may persist for several hours or days. In some cases symptoms may take 48 hours to emerge.
Some people are intolerant to several groups of foods, making it harder for doctors to determine whether it might be a chronic illness or food intolerance. Identifying which foods are culprits can take a long time.
According to the Australian NSW Food Authority2, the following are the most common symptoms of food intolerance:
Lactose in milk products is a common food intolerance
- Runny nose
- Feeling under the weather
- Stomach ache
- Irritable bowel
Causes of food intolerance
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 needed to fully digest foods. If some of these enzymes are missing or insufficient, proper digestion may be undermined.
People who are lactose intolerant do not have enough lactase, an enzyme that breaks down milk sugar (lactose) into smaller molecules that the body can break down further and absorb through the intestine. Lactose cannot be absorbed through the gut wall into the bloodstream. If it remains in the digestive tract it can cause spasm, stomachache, bloating, diarrhea and gas.
People with an allergy to milk protein have similar symptoms to those with lactose intolerance; that is why lactose intolerant individuals are commonly misdiagnosed as allergic.
Researchers from Mary Bridge Children's Hospital and Health Center in Tacoma, WA, USA, found that fructose intolerance is common in children with recurrent or functional abdominal pain.3
Nearly all foods require an enzyme for proper digestion. According to the British Allergy Foundation4, enzyme deficiencies are common causes of food intolerance.
2) Chemical causes of food intolerance
Certain chemicals in foods and drinks can cause intolerance, including amines in some cheeses, and caffeine in coffee, tea and chocolates. Some people are more susceptible to these chemicals than others.
3) Food poisoning - toxins can cause food intolerance
Some foods have naturally-occurring chemicals that can have a toxic effect on humans, causing diarrhea, nausea and vomiting. Undercooked beans have aflotoxins that can cause extremely unpleasant digestive problems. Fully cooked beans do not have the toxin. Hence, people may wonder why they react to beans after one meal, and not after another.
4) Natural occurrence of histamine in some foods
Some foods, such as fish that has not been stored properly, can have an accumulation of histamine as they "rot". A number of people are particularly sensitive this naturally-occurring histamine and develop skin rashes, abdominal cramps, diarrhea, vomiting and nausea. Often, the symptoms are similar to anaphylaxis (a strong allergic reaction).
5) Salicylates are present in many foods
Salicylate intolerance, also known as salicylate sensitivity occurs when somebody reacts to normal amounts of ingested salicylate. Salicylates are derivatives of salicylic acid, which occurs naturally in plants as a defense mechanism against harmful bacteria, fungi, insects and diseases.
Citrus fruits have high levels of salicylates
Salicylates are found in many foods. Most of us can consume salicylate-containing foods without any adverse effects, but a number of people suffer symptoms after eating large amounts. Salicylate intolerant individuals should avoid foods that are high in salicylates.
Salicylates are present in most plant-sourced foods, including the majority of fruits and vegetables, spices, herbs, tea and flavor additives. Mint-flavoring, tomato sauce, berries, and citrus fruits have particularly high levels of salicylates. Processed foods with flavor additives are usually high in salicylates as well.
On the next page we look at how food additives are common causes of food intolerance and how food intolerance is diagnosed.