Many people experience unpleasant reactions to foods they have eaten and suspect a food allergy is the underlying cause. However, only 2–5% of adults and 2–8% of children are truly allergic to certain foods. The remainder of people may be experiencing food intolerance, or food sensitivity, rather than true food allergy.

“Masked” or “hidden” allergies are a controversial topic; many conventional doctors believe they are rare, whereas practitioners of alternative medicine believe they are extremely common. According to James Breneman, M.D., former chairman of the Food Allergy Division of the American Academy of Allergy, unrecognised food allergies are responsible for 60% of all of the symptoms seen by a family physician that are not adequately diagnosed or treated.

Food allergies and intolerance are best treated by avoidance of the offending food for a prescribed period of time, followed by a “rotation” diet, in which problem foods are only eaten every three to four days, instead of daily. Young children can often re-introduce foods after three months of avoidance, whereas adults may require six to twelve months of avoidance. Most hidden allergies are cyclic (i.e., they settle down after long-term avoidance). Fixed allergies (those that cause a reaction, no matter how long a time the food has been avoided) are less common.

Symptoms of food allergy or intolerance may not be triggered immediately after reintroduction of the foods; therefore, a person can get an erroneous impression their allergy or intolerance is cured. With repeated ingestion of the food, however, symptoms may gradually return. When a problem food is rotated, symptoms are less likely to return. Some doctors recommend rotating food groups (such as pulses every other day) in addition to rotating specific foods. The importance of rotating foods varies from person to person and may be related to the severity of the allergies.