That conclusion comes from the tracking of roughly 600 adults who had been between 15 and 100 pounds overweight when they embarked on either a low-fat or low-carb supervised diet for a year.
"In short, we hypothesized that we would be able to use information from previous studies of the past decade to come up with factors that we could test that would help determine which diet is better for whom," explained study author Christopher Gardner.
But both diets prompted similar weight loss, he said. What's more, Gardner and his colleagues did not gain any new insight as to why some people seem to lose more weight than others, regardless of which approach they embrace.
"The data and results we generated will not help clinicians guide patients, or [help] people to pick for themselves, one of these diet approaches over the other," he acknowledged.
Gardner is a professor of medicine with the Stanford Prevention Research Center's department of medicine at Stanford University Medical School.
In the study, participants were between the ages of 18 and 50. Roughly six in 10 were women.
Study participants were not told to count calories, but rather to restrict either fat intake or carb intake. The dieters were told to avoid unhealthy low-quality "shortcuts," such as processed junk foods that happen to be labeled "low-fat" or "low-carb," according to the report.
Dieters were also advised to cook for themselves as much as possible; to snack less; to eat with family and friends; to avoid dining while watching TV; to avoid sugar and refined grains; to eat lots of vegetables; and to choose whole foods whenever possible.
By the end of the study period, the investigators found a wide range of results. Some dieters lost as much as 60 pounds, while others gained as much as 20.
But as to why, Gardner said the jury is still out. He noted, for example, that genetic testing failed to pinpoint any sign that would predispose a dieter to either lose or gain weight, regardless of dietary approach.
Blood tests to track insulin levels also failed to identify any underlying metabolic predisposition towards weight loss or gain while dieting.
That said, when comparing the low-carb group and the low-fat group, the team found very similar results.
On average, weight loss among the low-carb participants was 13 pounds by the end of the year. Among low-fat dieters, that figure was 12 pounds.
The findings were published in the Feb. 20 issue of the Journal of the American Medical Association.
Connie Diekman is director of university nutrition at Washington University in St. Louis. "As a registered dietitian, the outcome of the study does not surprise me," she said.
"While it would be nice to find a way to determine the best diet for an individual, from this research it is clear that we aren't there yet," she said.
"Therefore, this study helps me have evidence to support a recommendation that the most important aspect of weight loss is finding an eating pattern that meets nutrient needs, manages your calorie intake at a level that is lower than your calorie burn, and is enjoyable," Diekman added.
Samantha Heller, a registered dietitian, further cautioned that "dieting, per se, does not work." Heller is a senior clinical nutritionist at New York University Medical Center.
Dieting "represents a temporary, often punitive approach to weight loss. And we lose sight of the important notion that it is more important to be healthy than skinny," she said.
"I encourage my patients to follow a balanced, healthy, mostly plant-based, approach to eating and to monitor portions," Heller explained.
For many people, she said, this requires a willingness to "ascend a learning curve that includes creating new lifestyle habits, shopping, cooking and food prep techniques, trying new foods and creating strategies to help manage chaotic schedules, families and life's ups and downs."More information
There's more on healthy eating at the U.S. National Heart, Lung, and Blood Institute.
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