Strong evidence lacking on food allergies

A review of previous research indicates that there are few high-quality studies on food allergies, with limited uniform criteria for making a diagnosis and determining prevalence and effective treatments, according to an article in the 12 May issue of JAMA.

Food allergies can have significant harmful effects on family economics, social interactions, school and work attendance and health-related quality of life. "However, currently licensed treatments target only the symptoms of reactions and anaphylaxis [severe allergic reaction], not the allergies themselves," the authors write. There is no clear consensus regarding the prevalence or most effective diagnostic and management approaches to food allergies, according to background information in the article.

Jennifer J. Schneider Chafen, MD, MS, of the VA Palo Alto Healthcare System, Palo Alto, and Stanford University School of Medicine, Stanford, Calif., and colleagues reviewed the available evidence on the prevalence, diagnosis, management, and prevention of food allergies. For this analysis, the researchers identified 72 studies that met criteria. The studies reported data on food allergies to cow’s milk, hen’s egg, peanut, tree nut, fish, and shellfish, which account for more than 50 percent of all allergies to food.

The researchers write that their review found several key results:

Food allergies affect more than 1 percent or 2 percent but less than 10 percent of the US population. Whether the prevalence of food allergies is increasing is not well established.

Food challenges, skin prick testing, and serum food-specific immunoglobulin E all have a role to play in making the diagnosis but no one test has sufficient ease of use or sensitivity or specificity to be recommended over the other tests. Numerous other proposed diag­nostic tests are of uncertain value due to lack of evidence.

Although elimination diets are the mainstay of therapy, the researchers identified only one randomised controlled trial (RCT) of an elimination diet. "Many authorities would consider RCTs of elimination diets for serious life-threatening food allergy reactions unnecessary and unethical; however, it should be recognised that such studies are generally lacking for other potential food allergic conditions…"

Immunotherapy, although currently not a licensed method for the treatment of food allergy, may be effective in generating desensitisation, but whether this treatment can also generate long-term tolerance remains to be determined. The safety of immunotherapy is likely to vary with the food allergen and the route of therapy administration and, to date, has not been adequately studied.

Among high-risk infants, hydrolysed formula may prevent against cow’s milk allergy but standardised definitions of high risk and hydrolysed formula do not exist. Probiotics in conjunction with breastfeeding, hypoallergenic formula, or both may help prevent food allergy but their independent effects remain unclear.

"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," the authors write.

(Source: JAMA/Archives: JAMA: May 2010)