Food allergies seem to proliferate, despite lack of evidence, definitions, tests

Overreporting and the lack of good definitions and diagnostic methods contribute to the appearance of more food allergies than may actually exist, according to a new study. Nearly one-third of people think they have food allergies, when less than a tenth actually do. And the treatments for food allergies not only lack evidence, but may actually create undernourishment in children.

Researchers conducted a systematic review of English-language articles indexed between January 1988 and September 2009, and reported their conclusions in the May 12 Journal of the American Medical Association.

Diagnostic tests were included if they had a prospective, defined study population, used food challenge as a standard and had enough data to calculate sensitivity and specificity. Researchers also included systematic reviews and randomized controlled trials. Of 12,378 citations, 72 met the criteria. Researchers reported findings for the foods that make up more than half of all food allergies: cow's milk, hen's egg, peanut, tree nut, fish and shellfish.

From the literature, researchers concluded:

• Food allergies affect more than 1% or 2% but less than 10% of the U.S. population. It cannot be established if this rate is rising.Food challenges, skin prick testing and serum food-specific IgE all play a role in diagnosis, but no test is easier than the others, nor are any tests more sensitive or specific enough to be recommended over another. Other proposed diagnostic tests lack enough evidence to prove value.Elimination diets are the mainstay of therapy, despite having only one randomized controlled trial. Potential benefits need to be weighed against the potential nutritional risks of such a diet, particularly in children. More controlled studies in patients with non-anaphylactic symptoms are needed.Immunotherapy may generate desensitization, but it's not licensed, it may not work long-term, and it may vary by food allergen.Hydrolyzed infant formula may prevent cow's milk allergy, but there's no definition of a "high-risk infant" or of "hydrolyzed formula." Exclusive breastfeeding isn't proven to prevent atopic disease. Probiotics and breastfeeding or hypoallergenic formula may prevent food allergy, but their independent effects aren't clear.

Researchers wrote, "This systematic review of food allergies found that the evidence on the prevalence, diagnosis, management, and prevention of food allergies is voluminous, diffuse, and critically limited by the lack of uniformity for the diagnosis of a food allergy, severely limiting conclusions about best practices for management and prevention."