March 1997
MIAMI BEACH, Fla. — Two thousand years ago, Hippocrates observed, "What is food to one is to others bitter poison." Today, pediatricians continue to diagnose and treat food allergy, sensitivity and intolerance.
William Byrne, MD, explained the subtle differences among the terms used to describe reactions to foods at the 32nd Annual Pediatric Postgraduate Course sponsored by Miami Children's Hospital.
"Pediatricians are asked by parents to explain a number of signs and symptoms. Some of these may be gastrointestinal, some of these may be more systemic, and all too often we attribute these to food. Food allergy is grossly overdiagnosed," said Byrne, who is medical director/senior vice president for medical affairs, Children's Hospital, and clinical professor of pediatrics, University of California San Francisco.
For example, no scientific evidence supports theories that foods cause colic, nonspecific diarrhea of infancy, inflammatory bowel disease, enuresis, allergic-tension-fatigue syndrome or hyperactivity.
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One of the reasons for overdiagnosis is that terms describing distinctly different conditions are often used interchangeably.
"When we talk about food allergy, we are talking about an IgE-mediated reaction, which occurs within one hour after the ingestion of the offending antigen," Byrne said. "It's an immunologic reaction. When we talk about food sensitivity, again we are talking about an immunologically mediated reaction, but the onset of symptoms may be anywhere from 24 to 48 hours after ingestion of the offending antigen. When we talk about food intolerance, we are not talking about an immunologically mediated reaction. A food intolerant reaction is to a particular component of the food. It is reproducible. ... Food aversions have a psychological etiology in the sense that they are not necessarily reproducible on blind challenge. They are not physiologically mediated."
A number of factors contribute to food sensitivity. Genetics clearly plays a role, as does the amount of early antigen exposure. The development of IgA may offer some protection.
Food intolerance is a reproducible reaction to components of particular foods; however, it is not immunologically mediated.
The mechanism of food intolerance may be pharmacologic, microbiologic (i.e., contamination or toxin) or metabolic (i.e., related to carbohydrate intolerance). Carbohydrate intolerance, particularly lactose intolerance, is the most familiar.
Sucrase-isomaltase deficiency is a rare type of food intolerance. There is a lack of sucrase activity with decreases maltase and isomaltase activity. Because there is glucoamylase activity, children are able to tolerate starch.
"As soon as sucrose is introduced into the diet, early in infancy, you usually begin to see diarrhea," Byrne said. "The diagnosis can be made on the basis of a history, but generally an oral sucrose tolerance test or breath hydrogen test can confirm the diagnosis, or brush border enzyme measurement. The treatment during the first year is to avoid all starches and sucrose. So you can see it is difficult to treat. Remember that most of the suspensions that we prescribe do contain sucrose, so if you have an infant with [sucrase-isomaltase deficiency], you have to avoid those. Early in childhood, the children are able to tolerate small amounts of starch, but again you must continue to avoid sucrose."
Finally, pediatricians may see a case of food aversion: psychological fears of reactions to particular foods. There is no physiological basis for the aversion, and diagnosis is made with a blind challenge.
Regardless of whether the child is allergic, sensitive or intolerant to a particular food, the diagnosis is made with a careful history and physical exam.
"Be careful of an elimination diet. Skin testing is a reasonable alternative. Those foods with a positive skin test can be eliminated from the diet and then systematically, either in open challenge or a double-blind challenge, add it back to the diet and see whether there is a reaction," Byrne said.
For more information:
- Ferguson A. Food sensitivity or self-deception? N Engl J Med.1990;323:476-78.
- Ferguson A. Definitions and diagnosis of food intolerance and food allergy: Consensus and controversy. J Pediatr. 1992; S7-11.
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