The Better Diet for Long-Term Weight Loss, According to Harvard Scientists

Good news: It includes fat. (Photo: Getty Images)

At a time when experts are mixed on the role of fat in our diets, a new review from Harvard University has found that low-fat diets aren’t the most effective way to lose weight — and keep it off.

The research, which was published Friday in The Lancet: Diabetes & Endocrinology, analyzed 53 clinical trials and discovered that low-fat diets don’t help people lose weight and maintain that weight loss for more than a year as well as diets that contain higher amounts of fat.

Researchers discovered that, on average, study participants on low-fat diets lost and kept off six pounds after a year, while those that followed low-carb diets (which contained more fat) lost about 8.5 pounds within a year.

Lead study author Deidre Tobias, ScD, an instructor and epidemiologist at Harvard Medical School and Brigham and Women’s Hospital, tells Yahoo Health that she was — and wasn’t — surprised by the results.

“Everyone has been promoting low fat diets for decades and we’re still chasing an obesity epidemic,” she says. “We knew something wasn’t right in the message we were promoting.” However, she says she was surprised at how ineffective the low-fat diets were in the long run compared to other diets.

The findings come just months after the Dietary Guidelines Advisory Committee (a group of independent scientists who review scientific literature on nutrition and give recommendations to the U.S. government) proposed removing the fat restriction guidelines from our daily diets — for the first time since 1980. (Current guidelines suggest no more than 35 percent of our daily calories should come from fat.)

Bad Fats Are Still Bad, Though

Some scientists argue that there should be no limit on fat in our diets. In a paper published in the Journal of the American Medical Association, researchers argue that all fats aren’t created equal. Eating foods that contain healthy fats, like nuts, olive oil, and fish, can actually protect us against heart disease and other diseases, they said, while many low-fat and fat-free foods can be worse for our health than full-fat options.

Tobias agrees that fats aren’t created equal, noting that “bad fats are still bad fats.” She urges people to limit the amount of saturated fat and trans fats they consume — both of which have been linked to an increased risk of developing heart disease.

Why Don’t Low-Fat Diets Work as Well as Others?

Tobias says adherence is an issue. “Sticking to a diet, whether it’s high-fat or low-fat, in the long-term seems to be difficult for people,” she says.

Registered dietitian-nutritionist Karen Ansel, co-author of The Calendar Diet: A Month by Month Guide to Losing Weight While Living Your Life agrees, noting that low-fat diets aren’t as satisfying as plans that allow you to enjoy a little fat. “Fat takes a long time to digest so it keeps you full,” she tells Yahoo Health. “Plus, fat gives food flavor, so you’re less likely to suffer from diet boredom and end up cheating.”

Related: The 20 Best Full-Fat Foods for Weight Loss

Tobias also says there’s a potential issue with what people often eat in place of fats. “For low fat diets, people were swapping out good sources of fat like olive oil and nuts for sugars and refined carbohydrates,” she says. “Even if people were able to stick with a low-fat diet, that didn’t lead to much change when they replaced good things with bad things.”

Jonathan Sackner-Bernstein, MD, a cardiologist and former FDA official who conducted a meta-analysis on the effectiveness of low-carb vs. low-fat diets that was published in the journal PLOS-One earlier this month echoes the low-fat sentiment.

“When we were writing our paper, we tried very hard to find the evidence to support the recommendation for low fat diets. There is not convincing/consistent data to support it,” he tells Yahoo Health. “Low fat should not be the recommendation or goal.”

Related: The Worst Type of Fat for Your Health Has Been Identified

Sackner-Bernstein’s research analyzed randomized-controlled trials on nearly 1,800 obese and overweight participants and found that low-carb diets outperformed low-fat diets in terms of weight loss and participants’ risk of developing heart disease.

While Tobias says focusing on fat alone when it comes to weight loss is often ineffective, she also argues that people need to think more long-term about their eating habits.

“Using total fat as your only guide is misleading and can lead you to make several poor choices,” she says. “We need to turn the message away from fat vs. carbs, low-fat vs. high fat, and instead focus on the foods that are good for us for long-term success.”

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