Some common types of food intolerance are:
- histamine, present in mushrooms, pickles, and cured food
- additives such as artificial sweetners, coloring, or other flavorings
Some people experience a reaction after eating bread, but this does not necessarily indicate a gluten intolerance. Anyone who suspects they may have a gluten intolerance should see a doctor before giving up gluten, as cereals can be an important source of various nutrients.
Food additive intolerance has been a steadily-growing problem over the last thirty years because more and more foods contain additives.
Even so, food additive intolerance is not estimated to affect more than 1 percent of people.
Additives are used to enhance flavors, make foods look more appealing, and to increase their shelf life. Examples of food additives include:
- Artificial colorings
- Artificial flavorings
- Flavor enhancers
Of the thousands of additives used in the food industry, a relatively small number are thought to cause problems. The following food additives are known to cause adverse reactions in people:
- 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).
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.
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.
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.
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.