Feb. 10, 2015 -- For years we’ve been told to eat a low-fat diet to protect ourselves from heart disease.
But a new report says those guidelines -- which recommend keeping fat to 30% or less of daily calories and saturated fat to 10% or less -- were not backed by solid research when they were first issued decades ago.
The report’s authors even say dietary advice “should not have been introduced” at all.
U.S. public health officials made the recommendation in 1977, and 6 years later those in the U.K. did the same, in efforts to curb heart attacks and heart disease.
Officials acknowledged the evidence wasn't conclusive when the guidelines were issued. The authors of the new report say that's an understatement.
"The evidence was never there," says James J. DiNicolantonio, PharmD. He's a research scientist at St. Luke's Mid America Heart Institute in Kansas City, MO.
The new report echoes concerns of other experts, says Steven Nissen, MD, chair of cardiovascular medicine at the Cleveland Clinic. He says there needs to be a major shift in how doctors advise their patients on diet. Nissen was not involved in the new report.
A Look Back at the Studies
With his colleagues, DiNicolantonio searched medical databases to find studies that drove the recommendations. They found six relevant clinical trials that looked at the relationship between dietary fat, cholesterol levels, and heart disease.
The trials found that eating a lower-fat diet didn't reduce deaths from heart disease or any other cause, he says. In one case, a group that limited its saturated fat to 10% had more deaths from heart disease and other causes than those who didn't follow the 10% rule, he says.
Here are some other issues they found:
- The studies included more than 2,400 people, all of them men. There was no difference in death rates between men who ate low-fat diets and those who didn’t. Men in both groups were as likely to die of heart disease.
- All but one of the studies looked only at men who'd already had a heart attack, not at those who hadn't yet gotten heart disease.
- Although men who ate less fat had lower cholesterol, they weren’t less likely to die of heart disease or other causes.
- Five of the six studies used different approaches to reduce fat in people’s diets. Only one had participants follow the guidelines recommending that people eat less than 30% fat overall or 10% saturated fat.
Reactions to the Report
At the time the guidelines were issued, the field of what is now known as ''evidence-based medicine'' was just beginning, says Vasan Ramachandran, MD. He's a professor of medicine at Boston University. He wasn't involved in the new research, but he is the principal investigator of the Framingham Heart Study, launched in 1948 to spot common factors leading to heart disease.
The public health experts who looked at the proposed recommendations analyzed the evidence available at the time and made an informed judgment, he says.
While debate about the best dietary approaches for heart health is ongoing, keeping cholesterol low does matter, Ramachandran says.
Large trials show that lowering cholesterol by a lot in turn lowers the risk of cardiovascular disease, he says. Cutting cholesterol with statin drugs has benefited millions, he adds.
Even if evidence backing up the decades-old guidelines is lacking, there is evidence of a link between dietary fat and heart disease, warns Rahul Bahl of the Royal Berkshire NHS Foundation Trust in the U.K. But he says saturated fat isn't the only heart disease ''villain,'' with some data showing carbohydrates should share some of the blame.
What to Do?
Experts disagree on what to do about fat in the diet for heart health. "We are genetically designed to be eating saturated fat and animal fat," DiNicolantonio says. But he recommends eating whole foods. "A whole food is something you can pick from a plant, milk from a cow, or pull from the ground," he says.
Try to get to and stay at an ideal weight, whether you use a low-carb or low-fat diet, Ramachandran says. When you stick to a healthy weight and exercise regularly, it can help minimize your risk of heart disease, he says -- although that's provided you don't smoke, have diabetes, or uncontrolled high blood pressure or high cholesterol.
Until more research is done, Nissen says people should try to follow the Mediterranean diet. It includes fruits, vegetables, healthy fats like olive oil, oily fish, whole grains, nuts and legumes, along with moderate amounts of red wine.
Nissen says research shows that people at high risk for heart disease who ate a Mediterranean diet had fewer heart problems than those who followed a low-fat diet.
The American Heart Association still backs a low-fat approach. In its current guidelines, the AHA recommends keeping total fat to 25% or 35% of calories daily and saturated fat to less than 7%.