“It’s the most egregious abuse of data I’ve ever seen,” says Walter Willett, MD, DrPH, a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, who was among the signers of the letter. “There are just layers and layers of problems.,”

Because the analyses didn’t dig into what else participants were eating, the NutriRECS researchers asked the wrong question, says THI. Were they replacing red meat with tofu, or fried chicken? “The right question would be to compare people eating red meat and processed meat to people eating a plant-based diet,” Ornish says. “It’s a very different conclusion.”

But most guidelines don’t depend on those observational studies alone — they also take into account randomized controlled studies of things like high blood pressure, which is considered an intermediate step toward heart disease, says Sievenpiper.

“It leads back to this misconception that nutrition is hard and confusing, that we don’t know how to eat, that doctors can’t agree,” says Jennifer Lutz, executive director of True Health Initiative. “We do know the best diet for human health and also the planet