Low-fat diets are no better for long-term weight loss than high-fat ones, according to a new analysis of several studies.
A team led by Deirdre Tobias at the Harvard School of Public Health analyzed 53 experiments, each lasting at least one year, that placed participants on different types of diets — some low-fat, some high-fat and low-carb, and so on.
"There is no good evidence for recommending low-fat diets," said lead author Tobias in a press release issued along with the study. "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."
The team analyzed only randomized, controlled trials — clinical experiments that are considered to be better at establishing clear cause-effect relationships than other methods are.
The researchers found that low-fat diets prescribed to study participants did not result in greater weight loss over time when compared with other approaches implemented with the same intensity.
"Intensity" refers here to the amount of contact researchers had with participants during a trial, or in other cases, how rigorously researchers altered study subjects' diets.
The team went as far as saying that "health and nutrition guidelines should cease recommending low-fat diets for weight loss in view of the clear absence of long-term efficacy when compared with other, similar intensity dietary interventions."
In fact, in some of the trials they studied, "higher-fat, low-carbohydrate" diets led to modestly greater weight loss than low fat ones.
However, across all the studies they examined, patients lost only around six pounds on average, Tobias told CNBC in an interview, so any differences between the low carbohydrate diets and other diets is small, and not enough to reverse the obesity epidemic in the United States.
Other diets with higher fat content showed similar results as the low-fat groups.
"I think the emphasis needs to shift away from fat, carbs and protein and toward focusing on actual foods and eating patterns," Tobias said.
She also warned that "bad fats," such as saturated fats and trans fats, "are still bad."
"This is not a free ride to go out and eat all the butter and bacon you want, because we know these foods have other health effects," She said.
Tobias and her colleagues published their research Thursday in the journal Lancet Diabetes and Endocrinology.
More research will be necessary in order to find the best strategies for long-term weight loss and weight maintenance, the team wrote in its study.
This story has been updated to reflect that the researchers did not specifically examine trans fats or saturated fats in their research.