The Better Diet for Long-Term Weight Loss, According to Harvard Scientists
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.
“Behind current dietary advice to cut out the fat, which contains more than twice the calories per gram of carbohydrates and protein, the thinking is that simply reducing fat intake will naturally lead to weight loss. But our robust evidence clearly suggests otherwise.”
Supporters of high-fat, low-carb diets, such as the Atkins diet, can take little comfort, however, from the research, which was funded by the National Institutes of Health and the American Diabetes Association.
Although they worked better than low-fat diets, the researchers found that no diets worked particularly well in the long term, as defined as more than a year. There is sustained weight-loss for six months, but then many people stop losing weight and even regain it if they give up dieting. In the trials, people on low-carb diets only lost 1kg (2.2lbs) more, on average, than those on low-fat diets and the overall average weight loss after a year in the trials was 3.75kg.
Generally, study participants on a low-fat diet got less than 30% (and sometimes only 10%) of calories from fat. Those on high-fat and low-carb diets usually got at least 30% (and sometimes more than 60%) of calories from fat and less than 10% from carbs.
Of all the diets they looked at, which emerged the lightweight champion? None.
The main verdict was that there was no difference in weight loss between low-fat and high-fat diets. However, the low-fat diets fared slightly better than the low-carb diets; people had lost about 2.5 more pounds after at least a year. But the difference was small and the researchers did not think it would lead to any meaningful health benefits.
“We thought (comparing) low vs. high fat diets would help us identify the optimal diet, but it’s clear that just focusing on how much fat is in your diet is not what is going to help address the obesity epidemic,” said Dr. Deirdre Tobias, epidemiologist at Brigham and Women’s Hospital and Harvard Medical School. Tobias is the lead author of the study, which was published this week in The Lancet Diabetes & Endocrinology journal.