Unlike food allergy, where the reaction to a food can happen within minutes, food intolerance generally produces very slow responses to food. The symptoms may appear several hours after the food is eaten, or the following day, or even 48 hours later in the case of bowel symptoms. Because the food (or foods) in question are being eaten so frequently, there is no obvious link between the food and the symptoms. This effect was referred to as ‘masking’ by the early clinical ecologists, and the name ‘masked food allergy’ is still sometimes used for food intolerance.
For many of those with food intolerance, it is difficult to pinpoint a moment when the illness started. The symptoms can begin with mild problems that most of us take for granted, such as headaches or excessive tiredness or frequent bouts of indigestion. Over the years, there is a slow decline into ill-health, but it is often so gradual that the person does not really notice how bad things are getting. For some patients, however, food intolerance has a more definite beginning. It may follow on from a bad bout of influenza or other viral infection. Or it may stem from a course of antibiotics, such as those given before some operations eg hysterectomy. Where people have been exposed to toxic amounts of pesticides, or other synthetic chemicals, food intolerance sometimes sets in immediately afterwards.
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