Are you allergic, or simply intolerant?

As old Lucretius (95-55 B.C.) was fond of saying, "one man's meat is another man's poison". I don't know if Lucretius bit into a nut to which he was allergic, but he was definitely on the right track. Foods that are mother's milk to most of us, may dreadfully discomfit (sometimes even kill) an unfortunate few. Just how few is the subject of controversy as the idea spreads that a variety of symptoms (not just those of classical allergy) are caused by individual hypersensitivity to certain foods or, more correctly, substances in those foods. Many are convinced that food sensitivities have become more common and that food processing has something to do with it. The media, various unorthodox practioners and some groups of lay people have spread the "news"--and somewhere in the hornet's nest are a few facts concerning immunology, food technology, and quackery.

First, let's get the terminology straightened out. To help with this I've turned to the British Medical Journal. The words describing food sensitivity are imprecise and are often used to mean different things; surely the Brits can simplify matters. According to them "food sensitivity" can be used to describe a reproducible unpleasant reaction to a specific food or ingredient which one person gets but others don't. Right away we can see that this definition leaves out food poisoning; Socrates wasn't suffering from food sensitivity when the hemlock did him in. Rather, it was the insensitivity of his enemies, but that's another story. We might say, however, that Socrates suffered the ultimate adverse reaction to food.

"Food allergy" is commonly used as a broad term to explain physical reactions to certain foods but, technically speaking, should be confined to immunological reactions--a situation involving the immune system, specifically immunoglobulin E. "Food intolerance" covers a wide range of responses to food (not related to the immune system) including the lack of an enzyme (e.g., lactose intolerance in which the enzyme lactase is missing or deficient), an irritation (certain spicy foods), or complicated reactions such as gluten intolerance in people with celiac disease.There is even a psychological food intolerance covering psychosomatic reactions which don't occur when the same food is given in an unrecognizable form.

Diagnosis of food senitivity (allergy or intolerance) is a piece of cake when there is a characteristic early response to a food that is eaten at least occasionally. The patient often notices the association and tells the doctor the diagnosis. The prescription is easy: if you're allergic/intolerant to something, don't eat it. Sometimes, however, the guilty substance may be "hidden" as an ingredient in a manufactured product and might even have a name that isn't easily recognizable or readily identifiable as the offending material. Also, if you're sensitive to a whole raft of things, you could be courting nutritional deficiencies by avoiding them all...so a consultation with a registered dietitian is definitely in order.

A diagnosis becomes more difficult if the clinical reaction is delayed or varies or doesn't always happen. Such a reaction is also made more difficult to judge if someone else has already incriminated a food on circumstantial evidence (post hoc ergo propter hoc: after the fact, therefore caused by the fact) or because of a "prejudice" toward that food. Skin tests are used for suspected allergies and along with the patient, or in the case of a child, the parent, acting as a detective, the truth can usually be ferreted out as to which foods lead to which predictable reactions, and the diet is adjusted accordingly. The various strategies that can be used to identify the culprit(s) include: a diet diary in which a list is kept of all foods eaten and symptoms noted (this method is open to subjective bias, isn't suitable if the reactions are serious, and is difficult to interpret if the responsible agent is present in several foods). Suspect foods can be eliminated for about a week at a time but this has the same drawbacks as the aforementioned. An elimination diet followed by reintroduction of foods one by one involves the removal (for two to three weeks) of all foods that commonly provoke sensitivity reactions. One food is then added back every seven days. In an elimination diet (one of several) the meat least likely to cause a reaction is lamb; the least "offensive" cereal is rice; for vegetables it's peeled potatoes, carrots and lettuce, and in fruits it's pears. Water and sugar is permitted ad lib. Obviously, there's a risk of nutritional deficiency if this is carried on too long--and such trials should really be conducted with the guidance of a registered dietitian.

More exotic food sensitivities, but nonetheless a real pain to the sufferers, include favism, a type of anemia that results when particular people eat fava (broad) beans; "bitter lemon purpura" caused by the quinine in bitter lemon, and, of course, "Chinese restaurant syndrome"--a sensitivity to monosodium glutamate. Whatever the category in which they're placed, food sensitivities are a real menace; if you're not a victim, be thankful