In a scathing commentary published Tuesday in the Annals of Internal Medicine, one of the country’s leading cardiologists — Dr. Steven Nissen of the Cleveland Clinic — rips apart the supposed scientific rationale for the latest installment of the Dietary Guidelines for Americans, which were released in their finalized form to the public earlier this month.
“A detailed review of the new guidelines confirms a disturbing reality: the nearly complete absence of high-quality randomized, controlled clinical trials (RCTs) studying meaningful clinical outcomes for dietary interventions,” he writes. “The report repeatedly makes recommendations based on observational studies and surrogate end points, failing to distinguish between recommendations based on expert consensus rather than high-quality RCTs.”
“Unfortunately,” he adds, “the current and past U.S. dietary guidelines represent a nearly evidence-free zone.”
It is long past time, Nissen says, for the nutrition establishment to transition from the evidence-free zone “to an era where dietary recommendations are based on the same quality evidence that we demand in other fields of medicine.”
If not, he adds, dietary advice will continue to be left “to cult-like advocates, often with opposite recommendations.”
The Minnesota ‘misadventure’
In the commentary, Nissen focuses his criticism primarily on the guidelines’ recommendation about dietary fat and cholesterol. That particular “decades-long misadventure,” he says, can be traced back to the famous Seven Counties Study led by University of Minnesota physiology professor and obesity researcher Ancel Keys.
Begun in 1956 and funded by a grant from the U.S. Public Health Service, the study was first published in 1970 and linked intake of saturated fat and cholesterol to the risk for coronary disease. Before the study, Keys had already aggressively promoted the concept that dietary fat and cholesterol were closely related to the development of heart disease. He even appeared on the cover of Time magazine in 1961, advocating a low-fat diet as the solution to the coronary heart disease epidemic.
Critics have suggested that the Seven Countries Study was biased in favor of the hypothesis that dietary fat and cholesterol were critical factors in coronary disease. The study examined heart disease rates in Italy, Greece, Yugoslavia, Finland, the Netherlands, Japan, and the United States. Yet data were available for 22 countries. The researchers omitted countries, such France, where consumption of total and saturated fat are very high but the risk for heart disease remains low.
So convincing was Keys that even before his study was published, “the American Heart Association (AHA) took up the cause, recommending that Americans reduce dietary fat intake and substitute corn or soybean oil for butter,” Nissen adds. “Soon, margarine (with large amounts of trans fats) became the “heart-healthy” alternative to butter, eggs synonymous with unhealthy eating patterns, and low-fat diets the answer to the soaring rates of heart disease.”
Consequences and remedies
The promotion of low-fat, low-cholesterol diets has had serious consequences, according to Nissen.
“We reduced dietary fat but binged on carbohydrates and became increasingly obese,” he writes. “Type 2 diabetes grew into an epidemic that is now threatening to reverse decades of progress in reducing coronary heart disease incidence.”
“The obsession with low-fat diets has resulted in some extraordinary and bizarre food-marketing practices,” he adds. “I recently observed a large bag of fat-free gummy bears sitting on a grocery store shelf with the unmistakable implication that ‘fat-free’ equates to heart-healthy.”
In reality, says Nissen, we know very little about whether low-fat diets prevent heart disease. “The best available evidence,” he says, “does not clearly support the widely held belief that Americans should limit saturated fat and cholesterol in the diet.”
Nissen calls for federal agencies, such as the National Institutes of Health and the Centers for Disease Control and Prevention, to fund randomized, controlled clinical trials that test various dietary interventions.
“Properly performed studies may demonstrate that saturated fat and cholesterol are indeed nutrients of concern, but the opposite conclusion is also possible,” he says.
Until we have good, solid evidence, the American public is left, he adds, with “the current state of confusion.”
FMI: Unfortunately, the Annals of Internal Medicine has the full commentary behind a paywall, but you can read the first page on the journal’s website.