"There are numerous foods, some of which seem highly beneficial, that cannot be tolerated by some individuals and interfere with their ability to absorb vital nutrients. This is known as a food intolerance, and it is becoming an increasingly common problem. A food intolerance is not the same as a food allergy. Food allergies have a very sudden and dramatic effect, such as vomiting, a rash or, in severe cases, anaphylactic shock or even death.
Food intolerances, on the other hand, appear more slowly and have chronic, long-term symptoms. For this reason, they are sometimes referred to as hidden, masked or delayed allergies. The lengthy list of symptoms includes skin conditions, such as acne, eczema and psoriasis; digestive disorders, for example colitis and irritable bowel syndrome; weight problems; hyperactivity and other behavioral problems in children; rheumatoid arthritis and osteoarthritis; insomnia, headaches, migraine and exhaustion; and a range of psychological problems, such as depression.
One common culprit is wheat, and people whose diet centers on bread, cakes, crackers and pasta can develop an intolerance to wheat. Processed foods, savory snacks and sweets can also cause problems. Many of the foods which cause intolerances are, curiously, often staples in a person's diet or foods that they crave, such as chocolate or coffee. This is because the sufferer's body not only adapts to the intolerance, buy becomes dependent on it. The food acts on the system as a toxin, and the body, unable to absorb it in the normal way, reacts against it. Problems flare up elsewhere that seem quite unconnected with the offending food, especially as the reaction takes place several days later, so the culprit foods remain a mystery.
Further confusion is caused by the different effects that a food intolerance may have. Wheat, for instance may cause migraine in one person but eczema in another. Another problem is the multiplicity of symptoms. Typically, one person might have alternating constipation and diarrhea, migraine, rheumatoid arthritis and a general feeling of such lassitude that he or she can hardly get out of bed in the morning.
One of the ways in which nutritionists pinpoint a food intolerance is by an elimination diet, in which a very bland diet is first established and then foods are introduced, one by one, to monitor whether they have an effect. If they don't, they can be included in the diet once more. If they do, this is clearly the sign of an intolerance and they should be excluded permanently."
Taken from the book "Miracle Foods" by Anna Selby