If the No. 1 rule for infant feeding is "breast is best," the No. 2 rule would have to be that parents should never introduce potential allergens to babies before their first year. But new evidence suggests that this age-old advice may have it all wrong. Now, researchers are testing the theory that exposing babies to peanuts — one of the most likely allergens — may actually prevent the future development of allergies.

A recent study, called the LEAP (Learning Early About Peanut Allergy) study, found that babies who were exposed to peanuts within their first 11 months of life were less likely to develop a peanut allergy than their peanut-avoiding peers. Among the 600 participants, 35 percent of the children who were not exposed to peanuts tested positive for peanut allergies after the first year compared to just 11 percent of the babies who were given peanuts as babies.

But could the allergy immunity be sustained over time? That question was answered by a follow-up study which was published recently in the New England Journal of Medicine. Researchers checked back in with 556 of the original participants in the LEAP study and asked half of them from both groups (the early peanut eaters and the peanut avoiders) to stop eating peanuts for one year starting at age five.

Researchers found that after one year, there was no statistical difference between the groups in the number of children who showed a sensitivity to peanuts after not eating them for one year. This suggests that the children who were exposed to peanuts as babies remained protected from peanut allergies, even if they did not sustain exposure on a daily basis.

In light of this research, the National Institute of Allergy and Infectious Diseases proposed new guidelines recommending peanut exposure for children at risk of peanut allergies starting at 4 to 6 months of age. These guidelines are contingent upon prior allergy testing to make sure that the infants are not already allergic to peanuts. This is a 180-degree change from the previous guidelines which recommended that all babies — and especially those at risk of developing peanut allergies — should avoid peanuts for at least the first year of life.

Would early exposure work similarly for other high-risk allergens such as eggs, wheat and fish? Those studies have not yet been conducted, but experts say that evidence suggests that early exposure — not avoidance — may just be the key to future allergy prevention.