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When we use sound scientific studies to make recommendations, we shine—and help a lot of people. But when we wing it and issue recommendations based on opinion, we have a lousy track record. Sometimes you’ll see that consensus is not driven by science, but by peer pressure.

The American Academy of Pediatrics (AAP) 2000 recommendation

for children zero to three years old and pregnant and lactating mothers to avoid all peanuts if any child was considered to be at high risk for developing an allergy

is a case where they did not follow evidence-based medicine. It's a case of copycat guidelines: they copied a 1998 UK health department recommendation. That recommendation was based on

one sentence stating that moms who eat peanuts are more likely to have children with peanut allergies

and referred to a single study lacking support for that statement.

The report cited a 1996 British Medical Journal (BMJ) study. So I pulled that up and took a close look.

I couldn’t believe it.

The actual data did not find an association between pregnant moms eating peanuts and a child’s peanut allergy. But that didn’t matter: The train had left the station.

Bewildered by how the study seemed so badly misconstrued, I called its lead author, Dr. Jonathan Hourihane, a professor of pediatrics in Dublin. He shared the same frustration and told me he had opposed the peanut avoidance guideline when it came out. “It’s ridiculous,” he told me. “It’s not what I wanted people to believe.”

He had not been consulted on the national guideline.

Predictably

Peanut allergies soared. More concerning, extreme peanut allergies, which can be life-threatening, became commonplace in America.

Suddenly, emergency department visits for peanut anaphylaxis — a life-threatening allergic swelling of the airways — skyrocketed, and schools began enacting peanut bans.

As things got worse, many public health leaders doubled down. If only every parent would comply with the pediatrics association guideline, they thought, we as a country could finally beat down peanut allergies and win the war.

Immunologists had objected.

Gideon Lack, a pediatric allergist and immunologist in London, challenged the UK guideline. It “was not evidence-based,” he wrote in The Lancet in 1998. “Public-health measures may have unintended effects … they could increase the prevalence of peanut allergy.”

Two years later, the same year the AAP issued their peanut avoidance recommendation

Then they tried to dissuade with a study.

They found that Jewish children in Israel had one-tenth the rate of peanut allergies compared to Jewish children in the UK, suggesting it was not a genetic predisposition, as the medical establishment had assumed. Lack and his Israeli colleagues titled their publication “Early Consumption of Peanuts in Infancy Is Associated with a Low Prevalence of Peanut Allergy.”

However, their publication in 2008 was not enough to uproot the groupthink.

The medical community maintained the guidelines & wouldn't fund studies to corroborate.

Avoiding peanuts had been the correct answer on medical school tests and board exams, which were written and administered by the American Board of Pediatrics. Many in the medical community dismissed Lack’s findings and continued to insist that young children avoid peanuts. For nearly a decade after AAP’s peanut avoidance recommendation, neither the National Institutes of Health’s (NIH’s) National Institute of Allergy and Infectious Diseases (NIAID) nor other institutions would fund a robust study to evaluate the recommendation, to see if it was helping or hurting children.

Several years later

As things got worse, a dissenting Lack decided to conduct a clinical trial randomizing infants to peanut exposure (at 4-11 months of age) versus no peanut exposure. He found that early peanut exposure resulted in an 86 percent reduction in peanut allergies by the time the child reached age 5 compared to children who followed the AAP recommendation. He blasted his findings to the world in a New England Journal of Medicine publication in 2015, finally proving what immunologists like Buckley had known for decades: Peanut abstinence causes peanut allergies. It was now undeniable; the AAP had it backward.

Lack is now recognized as a hero in the field of allergy. But when he did his big study, he was heavily criticized.

It would take the AAP two years after Lack’s randomized trial was published to reverse its 2000 guidance for pediatricians and parents. It would also take two years for the NIH’s NIAID division to issue a report supporting the reversal.

It was "an embarrassingly simple study" the AAP failed to demand.