Why the medical advice on peanut allergies flipped in a generation

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In just 10 years, the science behind preventing peanut allergies in babies appears to have completely flipped, with countries including Canada now recommending giving infants allergenic foods within their first six months of life — rather than total avoidance.

Parents may be hesitant to introduce the foods, given how severe allergic reactions can be — but doctors say there are solid reasons to give the foods early and often.

The shift can be traced back to a pivotal clinical trial led by a doctor in the U.K., who confirmed that early exposure works. In a sign of how the findings continue to reverberate, in February researchers presented their findings based on the younger siblings of the original study's participants, which backs the importance of introducing peanut in the diet at an early age. 

What's more, a recent U.S. study suggests rates of peanut allergy in children under age three declined 43 per cent over the last several years, after feeding guidelines changed.

"It was a terribly exciting and important discovery," said Dr. Gideon Lack, a professor of pediatric allergy at King's College London and Evelina Children's Hospital, who led the original trial. 

Food allergy rates have plummeted since the 2016 publication of Lack's Learning Early About Peanut Allergy (LEAP) study. It compared peanut allergy cases among infants aged four to 11 months who were at high risk and were randomly assigned to either regularly eat the food in an age appropriate way or to avoid it.

Investigators expected to see a 40 to 50 per cent decline in peanut allergy; instead, they found a 81 per cent reduction. Lack said they celebrated the results with a shot of whiskey.

The team followed the children and found that the protective effect lasted.

A combination of events sparked Lack's initial interest in food allergies, starting in his pediatric training when a teen he was treating died due to an anaphylactic reaction to peanuts.

"A perfectly healthy person can from one moment to the other face a life-threatening or in that particular case fatal outcome," he said. "So that had an influence on me."

As a fellowship trainee in Denver, Colo., Lack worked on mice models of food allergy and saw how the rodents would become allergic after exposing them to egg or peanut protein through the skin. But if the mice were fed the foods at a very young age, they were protected from allergies. 

Later, Lack would regularly present at pediatric and allergy conferences. In 2003 in Israel, he was startled at the response to a question he routinely posed to doctors.

"I asked the audience, how many of you have seen a case of peanut allergy in the last year?" Lack recalled.