Food Allergy: Adverse Reactions to Food and Food Additives.
- T J DAVID, Professor of child health and paediatrics
Food Allergy: Adverse Reactions to Food and Food Additives. 2nd Ed. Edited by Dean D Metcalfe, Hugh A Sampson, and Ronald A Simon. (Pp 583; £75 hardback.) Blackwell Science, 1997. ISBN 0-865-42432-2.
Cricket and baseball both use a hard ball that can travel at over 100 miles per hour (160 km/hour), but there are many differences in how the games are played. Another transatlantic difference is the approach to individuals with suspected reactions to food. In North America, the recommended approach is to perform skin prick tests, followed by double blind placebo controlled food challenges, proceeding to dietary elimination of foods that have been thus proved to trigger an adverse reaction. Lacking, however, are controlled trial data to evaluate this strategy. Thus, for example, there are no randomised controlled trial data on what proportion of subjects with atopic dermatitis are helped in the short or long term by this type of North American regimen. In the UK, on the other hand, allergy tests are eschewed because of the very large numbers of false positive and false negative results, and double blind placebo controlled challenges are avoided because they are difficult to employ routinely in very small children. The latter is an important problem, given that many of the diagnostic questions arise in infants, since most children grow out of reactions to foods in the first few years of life. Instead, the UK approach, when the symptoms are sufficiently severe, is to embark on a therapeutic trial of selected food avoidance. In certain conditions, most notably atopic dermatitis and colic, this approach has been subject to randomised controlled trials, so far with relatively small numbers and rather disappointing results.
The rules of cricket are complex, and baseball even more so. This excellent book describes the rules, that is the available background knowledge, in some detail, but it is not a practical manual on how to play the game. Much, rightly, is devoted to mechanisms, and this is well done. Thus one possible approach for the future is to genetically engineer foods in order to remove proteins which trigger allergic reactions. For example, by introducing antisense genes, the amount of allergen in rice can be reduced. However, until genetically engineered peanuts are available that can be safely eaten by those with peanut allergy, we have to fall back upon our basic approach of dietary avoidance. Hyposensitisation or treatment with peptides does not receive much attention; both are still probably only on the horizon. Interestingly, the molecular acrobatics that make one antigen an allergen and another antigen a non-allergen remain poorly understood.
Not all reactions to foods are immunological. Many foods contain toxic substances. Examples discussed in this book include myristicin in nutmeg (causes psychosis), capsaicin in chili peppers (causes a ‘hot’ sensation), and histamine in cheese and yeast (causes abdominal pain and headache). Many aspects of reactions to foods are quite different in adults, and this is well covered in the book.