The following originally appeared on The Upshot (copyright 2016, The New York Times Company).
It has become an article of faith among many women I know to eliminate some foods during pregnancy, out of concern that their children could become allergic to them: shellfish, dairy and, most of all, peanuts.
After their babies arrive, they continue to abstain from certain foods while breast-feeding, and they certainly keep their children from eating them.
But research in the last few years has consistently shown that all this avoidance often does more harm than good. In many cases, we need to be doing the opposite.
Mothers didn’t adopt this behavior out of nowhere. In 2000, the American Academy of Pediatrics released guidelineson reducing a child’s risk for developing allergies. They recommended that mothers “eliminate peanuts and tree nuts (e.g., almonds, walnuts, etc.) and consider eliminating eggs, cow’s milk, fish, and perhaps other foods from their diets while nursing.”
Further, they recommended that children at high risk for allergies be given no solid foods until six months of age, no dairy products until 1 year old, no eggs until age 2, and no peanuts, nuts or fish until age 3.
A debate has been raging in the health care system for decades on this topic. I was part of a systematic review that examined the relationship between early solid food introduction and allergic disease in children. We found no good evidence to support the idea that being exposed to solid foods earlier led to persistent food allergies.
To its credit, the A.A.P. changed its recommendations based on new research. In 2008, updated guidelines reported that maternal restrictions in pregnancy or breast-feeding no longer seemed like advice that should be widely recommended. It also acknowledged that there didn’t seem much reason to delay the introduction of “allergy” foods like peanuts after six months, which is around the age babies move from milk or formula to a wider range of food.
Unfortunately, this did little to change people’s behavior. Many had already internalized the advice. It seemed logical to them that avoiding foods would give children less of a chance to develop allergies. If it was still a good idea not to expose children until they were six months old, why not keep going?
A study published in the New England Journal of Medicine last year turned all of this on its head. Researchers enrolled 640 infants at high risk for allergies, between 4 and 11 months of age, in a trial and randomized them to one of two groups. One of them was told to avoid peanut protein; the other was told to eat at least six grams of peanut protein a week given in three or more meals. All participants were followed until they were 5 years old.
What was most surprising in this work was that 15 percent of the infants already had evidence of peanut sensitivity by allergy testing. They were enrolled in the trial despite this, and half of them were given peanut extract every week.
The results were remarkable. At the end of the study, about 3 percent of those exposed to peanuts had developed a peanut allergy, compared with more than 17 percent among those who avoided peanuts.
More surprising, if you looked just at the children who already had evidence of peanut sensitivity when they were babies, fewer than 11 percent of those regularly exposed to peanuts developed an allergy. But more than 35 percent of those who avoided peanuts developed an allergy.
Children who had proven sensitivity to peanuts, but consumed them in their diet regularly, were less likely to develop a peanut allergy than children without sensitivity but who avoided them.
Recently, follow-up results were published. After the trial ended, researchers asked all the participants who had been regularly consuming peanuts to avoid them for the next 12 months.
At the end of that period, when the children were 6, there was no significant increase in new peanut allergies in that group. Avoidance at this point made no difference. The critical need for exposure appears to be somewhere from infancy until age 5.
These results were so convincing that, once again, experts are changing their recommendations. In September 2015, the A.A.P. — along with others— argued that “health care providers should recommend introducing peanut-containing products into the diets of ‘high-risk’ infants early on in life.”
These changes dovetail nicely within what has become known as the hygiene hypothesis, the gist of which is that as we’ve made our environment more and more sterile, our immune systems develop differently than they used to. Without exposure to outside things to fight, our defenses turn inward and toward more benign substances, leading to increased levels ofeczema, asthma and allergies.
Of course, many people used to die from infections that no longer threaten us because of advances, so no one should take this as a call for living in filth. Nor should anyone take these recent findings as advice to feed babies and small children peanuts and other foods without concern. All changes to an infant’s diet, especially in children with allergies, should be done in consultation with a health care professional.
As with many things in health care, however, we went too far with our response to peanut and other food allergies. Avoidance is sometimes needed for those with severe reactions. When we apply those same rules to everyone else, however, things can backfire.