Low-fat diets no help for weight loss in long run, review shows

The low-fat diet craze for weight loss should come to an end, say researchers who conducted a large review of diet studies.

Deirdre Tobias from Brigham and Women's Hospital and Harvard Medical School in Boston and her colleagues reviewed randomized trials comparing the effectiveness of low-fat diets to other diets and no diets for weight loss of at least one year.

The analysis of studies on more than 68,000 adults is published in Thursday's issue of The Lancet Diabetes & Endocrinology.

"When we tell people to just lower their fat intake, it hasn't worked," Tobias said in an interview. "That's what the message has been for several decades and it's only gotten us more obese, more overweight and clearly isn't the effective strategy."

Tobias said it's time to change our way of thinking from a focus on counting calories or grams of fat or carbs, to overall food intake.

"To reduce calories, what we should be doing is simple: reduce our portions."

Across all of the trials, after a year or more of cutting back on fat, on average the participants lost about six pounds, the researchers found.

Tobias and her team acknowledged limitations of the research, such as the suggestion of inconsistent effects across studies and the difficulty retaining participants for long-term lifestyle trials.

In weight loss trials, higher fat, low-carb diet plans led to a slight weight loss benefit, but the difference is "clinically insignificant," Kevil Hall of the U.S. National Institute of Diabetes and Digestive and Kidney Diseases said in a journal commentary published with the study.

"What seems to be clear is that long-term diet adherence is abysmal, irrespective of whether low-fat or other diets, such as low-carbohydrate diets, are prescribed," Hall said.

Doctors and dietitians agree the key is to stick to healthy lifestyle changes.

"Having worked with thousands and thousands​ of patients over the years, I can tell you that in many cases, low-fat diets aren't as filling," said Dr. Yoni Freedhoff, medical director of the Bariatric Medical Institute and an assistant professor of family medicine at the University of Ottawa.

"Although you're cutting your calories from your fat, you're hungrier. If you're hungrier, you eat more. Or you struggle to stick to your diet, and as a consequence, ultimately quit. "

Freedhoff advises people who want to make real improvement in their health to cook more, use fewer boxes of processed foods and drink fewer calories.

Unsaturated fats from plant sources such as nuts and seeds are a good choice for snacks.

But beware of marketers riding the low-fat bandwagon, Tobias said.

"You see low-fat versions," she said. "It's really taking something that's bad for you and making it probably even worse for you because if you take out the fat, you have to add things like sodium and sugar."

She encouraged people to be more flexible about what they eat to stick with the healthy changes.

The study was funded by the U.S. National Institutes of Health and American Diabetes Association.