The era of the low-fat diet may be nearing an end.
A new analysis by scientists at Brigham and Women’s Hospital and Harvard Medical School — using data from more than 50 randomized, controlled studies that, together, included more than 68,000 people — supported a contention that many scientists and dieters have already come to believe: A low-fat diet does not help people lose weight and keep it off in the long term any more than a high-fat diet does.
The researchers looked at studies comparing low-fat diets with other types of diets — or to no diet at all for at least a year. The results were clear: Low-fat diets weren’t any more effective than high-fat diets when it came to losing weight and sustaining that loss over a long period of time.
“In fact, in the setting of weight loss trials, higher-fat, low-carbohydrate dietary interventions led to a slight but significant, greater long-term weight loss than did low-fat interventions,” they wrote in a paper published on Thursday in the journal The Lancet Diabetes & Endocrinology.
More than one-third of American adults are obese, according to the Centers for Disease Control and Prevention, leading to an epidemic of obesity-related illnesses such as diabetes and cardiovascular disease in the United States. Scientists have debated the optimal proportions of fat, protein and carbohydrates, arguing over the merits of various approaches — from the Mediterranean diet, which focuses on plant-based foods and healthy fats including olive oil, to low-carbohydrate diets, which emphasize proteins and healthy fats and limit starchy grains and sugar.
The low-fat diet, the authors of the study wrote, was rooted in the idea that it would cut calories. For example, a gram (0.035 ounce) of fat has more than twice the calories of a gram of protein or carbohydrates, so limiting fats in the diet would mean eating fewer calories overall.
But studies examining low-fat diets didn’t always show that they were more effective than other types of diets.
“Our obsession with reducing total fat has completely failed us for weight loss,” Deirdre Tobias, an epidemiologist at Brigham and Women's Hospital and Harvard Medical School and lead author of the study, told Al Jazeera in an email. “It’s too vague and allows people to make too many poor food choices, and rates of overweight and obesity skyrocketed as a result.”
The researchers found that higher-fat diets actually resulted in “significantly greater” weight loss than the low-fat diets in the studies where those two groups differed by more than 5 percent of calories from fat.
In studies where the ultimate goal was weight loss, it was the low-carb diets that brought about more long-term weight loss than the low-fat diet plans. The only cases in which low-fat diets came out on top were in the studies in which they were compared to participants’ usual diets as an experimental control.
In other words, eating low-fat helped people lose more weight than eating whatever they felt like, but it wasn’t the best option.
Rather than worrying about some magical balance of protein, carbohydrates or fats, the researchers say healthy eating overall is far more important. “Our findings emphasize why we need to start thinking in terms of foods and overall healthy patterns for maintaining a healthy body weight, rather than focusing on individual nutrients like fats and carbs,” Tobias said.
She stressed that these results aren’t a green light for reckless abandon. People should still limit their consumption of saturated fats, which are found in red meats and some dairy products.
“But if we’re eating fruits and vegetables, whole grains, limiting our red meat intake, then these things will fall into place,” Tobias said.