It's often said that food allergies are a growing problem, but a new review in a prestigious medical journal suggests that no one knows if that's even true.
The authors of the new review in JAMA, the Journal of the American Medical Association, analyzed dozens of studies done on food allergies since 1988. They found there were few high-quality, definitive studies, and most of them had different criteria for what defines a food allergy.
The researchers found there was no clear consensus on how prevalent food allergies are, nor is there agreement of the best way to diagnose and treat such allergies.
For the analysis, Dr. Jennifer J. Schneider Chafen, of the Stanford University School of Medicine, led a team who reviewed 72 studies on the prevalence, diagnosis, management, and prevention of food allergies. The studies included allergies to cow's milk, hen's egg, peanut, tree nut, fish, and shellfish, which account for more than 50 per cent of all food allergies.
The team said they couldn't determine how prevalent such allergies were, but estimated they affect more than 1 or 2 per cent but less than 10 per cent of the U.S. population. (Rates are thought to be similar in Canada, where environments and lifestyles are similar to the U.S.)
As for whether food allergies were increasing, the team said there simply wasn't enough evidence from any of the studies to say for sure.
The team found there also wasn't agreement on how best to diagnose a food allergy. Skin prick testing, serum food-specific immunoglobulin E, and "food challenge" tests all have a role in making the diagnosis, they said. But no one test is either accurate enough or easy enough to perform to be recommended over the others.
As for how to treat food allergies, the researchers found that simply eliminating the allergenic food from the diet seems to be the most common method -- even though studies haven't actually proven that approach is best.
"The benefits of an elimination diet are uncertain based on published evidence, and potential benefits need to be weighed against the potential nutritional risks of such a diet, particularly in children," the authors write.
New immunotherapy treatments on the horizon are promising, the authors said. In this treatment, extremely tiny amounts of the allergenic food are introduced to the patient and then gradually increased over time, to help the immune system develop tolerance. But the authors say it remains to be seen whether these treatments can generate long-term tolerance.
"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 conclude.
They note, though, that "food allergy is a subject of much current study" and they "expect the evidence base about food allergy to change more rapidly in the near future than it has in the past."
