New light shed on preventing food allergies


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According to the Centers for Disease Control and Prevention (CDC), around 15 million Americans suffer from food allergies. The number of affected children went up by approximately 50 percent between 1997 and 2011. That means something like 1 in 13 of those under the age of 18 in the U.S. are at risk from having mild to severe reactions. In the ongoing quest for answers, a new review published in the Canadian Medical Association Journal (CMAJ) looks at methods of food introduction and allergy prevention.


A leap into the unknown


Though the reasons behind them are not entirely clear, food allergies have certainly increased over time. In a recent survey of Canadian households, 8 percent of people reported at least one food allergy with the most common allergens known to be cow's milk, soy, peanut, tree nuts, eggs, wheat, fish, shellfish and sesame. To make matters worse, babies with parents or siblings who have allergies, especially to peanuts, are at higher risk of atopy — the tendency to develop allergic symptoms.

According to WebMD, allergies begin when the body — for some reason — misidentifies some substance (even a familiar one) as a harmful invader. The body then creates antibodies to deal with the perceived threat and the  next time it is encountered the antibodies are released and special cells called "mast cells" are activated causing allergy symptoms in the lungs, the skin, and the lining of the nose and intestinal tract.

"If parents ask how to prevent allergy in their children," say the authors of the new study — a team at the Department of Pediatric Allergy and Clinical Immunology, University of Manitoba — "our current advice is to introduce the allergenic foods at four to six months of age." Early and often, they suggest, is the key. "Once highly allergenic foods are introduced," the team say, "regular exposure is important for maintenance of tolerance — children should eat these foods on a regular basis."

A recent randomized controlled trial — the Learning Early About Peanut (LEAP) study — found that, by introducing peanuts early rather than late in high-risk children, the risk of food allergy was reduced by as much as 80 percent. As a result of the LEAP study, some groups — such as the American Academy of Allergy, Asthma and Immunology, the American Academy of Pediatrics and the Canadian Society of Allergy and Clinical Immunology — now state that for infants at high risk, there is strong evidence to support the introduction of peanuts (in a practical and safe form like, say, peanut butter) between 4 and 11 months.


The best advice


It is extremely important, of course, to get the benefit of a qualified allergist's evaluation before introducing peanuts to children at high risk of peanut allergy. Previously, it was recommended that parents avoid giving potentially allergenic foods to children and babies at high risk until they were 12 to 36 months of age. As a consequence, some women have avoided potentially allergenic foods during pregnancy and breastfeeding to try to prevent the development of allergies in their babies. The new thinking does not support avoidance diets.

To introduce new foods, the American Academy of Allergy, Asthma and Immunology recommends:

1. Introducing a new food every three to five days in an age-appropriate manner (to avoid choking).

2. Starting with grains, yellow and orange vegetables and fruit.

3. Introducing one of the potentially allergenic foods, if well tolerated, in small amounts (e.g., cow's milk, soy, eggs).

4. Introducing highly allergenic foods at home.

5. Increasing the quantity of food over several days.

The idea that allergies can be prevented through early exposure to potential triggers is not a new one. Allergy experts have long discussed the so-called "hygiene hypothesis" — the idea that by attempting to protect ourselves from bacteria and irritants, we in the West actually make matters worse by not adequately exposing our immune systems to those very things which help us build up our defenses. The research shows us, apparently, that this is as true for certain foods as it is for bacteria, dirt or pollen.

"It has been well documented that avoidance of allergenic foods is not preventive of food allergy," say the Canadian team, which was headed by Drs. Elissa Abrams and Allan Becker. "In the newly released LEAP study, there is strong evidence that early introduction of peanut is in fact preventive. How this will change current guidelines on food introduction remains to be seen."

A podcast of an interview with the review's authors is available here