Why Almost Everything Dean Ornish Says about Nutrition Is Wrong

Melinda Wenner Moyer in Scientific American:

Last month, an op–ed in The New York Times argued that high-protein and high-fat diets are to blame for America’s ever-growing waistline and incidence of chronic disease. The author, Dean Ornish, founder of the nonprofit Preventive Medicine Research Institute, is no newcomer to these nutrition debates. For 37 years he has been touting the benefits of very low-fat, high-carbohydrate, vegetarian diets for preventing and reversing heart disease. But the research he cites to back up his op–ed claims is tenuous at best. Nutrition is complex but there is little evidence our country’s worsening metabolic ills are the fault of protein or fat. If anything, our attempts to eat less fat in recent decades have made things worse. Ornish begins his piece with a misleading statistic. Despite being told to eat less fat, he says, Americans have been doing the opposite: They have “actually consumed 67 percent more added fat, 39 percent more sugar and 41 percent more meat in 2000 than they had in 1950 and 24.5 percent more calories than they had in 1970.” Yes, Americans have been eating more fat, sugar and meat, but we have also been eating more vegetables and fruits (pdf)—because we have been eating more of everything.

What’s more relevant to the discussion is this fact: During the time in which the prevalence of obesity in the U.S. nearly tripled, the percentage of calories Americans consumed from protein and fat actually dropped whereas the percentage of calories Americans ingested from carbohydrates—one of the nutrient groups Ornish says we should eat more of—increased. Could it be that our attempts to reduce fat have in fact been part of the problem? Some scientists think so. “I believe the low-fat message promoted the obesity epidemic,” says Lyn Steffen, a nutritional epidemiologist at the University of Minnesota School of Public Health. That’s in part because when we cut out fat, we began eating foods that were worse for us. Ornish goes to argue that protein and saturated fat increase the risk of mortality and chronic disease. As evidence for these causal claims, he cites a handful of observational studies. He should know better. These types of studies—which might report that people who eat a lot of animal protein tend to develop higher rates of disease—“only look at association, not causation,” explains Christopher Gardner, a nutrition scientist at the Stanford Prevention Research Center. They should not be used to make claims about cause and effect; doing so is considered by nutrition scientists to be “inappropriate” and “misleading.” The reason: People who eat a lot of animal protein often make other lifestyle choices that increase their disease risk, and although researchers try to make statistical adjustments to control for these “confounding variables,” as they’re called, it’s a very imperfect science. Other large observational studies have found that diets high in fat and protein are not associated with disease and may even protect against it. The point is, it’s possible to cherry-pick observational studies to support almost any nutritional argument.

More here.