On Wednesday, nutrition researchers published what may one day be considered a landmark paper in the field of dieting. It calls for a more complex understanding of dieting, one that goes beyond an obsession with calorie cutting. If its results are replicated, this study is probably a win for low-carb dieters out there.
The paper, published in the British Medical Journal, is based in a cruel truth about weight loss: As weight decreases, the body makes minute adjustments that make it hard to keep weight off. The paper, whose co-principal investigator was David Ludwig, M.D., Ph.D., a professor of nutrition at Harvard’s T.H. Chan School of Public Health, puts forth a way that we might continue to keep the metabolic fire burning, by adhering to a high-fat, low-carbohydrate diet. Ludwig and his team showed this phenomenon in one of the larger feeding studies ever done on 164 adults at a hospital in Framingham Massachusetts.
“Our findings suggest that a more effective strategy to lose weight over the long term is to focus on cutting processed carbohydrates, not calories,” Ludwig wrote in an op-ed in the LA Times.
The trial began with 234 clinically obese adults who adhered to a 10-week weight loss program, in which their goal was to lose 10 percent of their body weight. The 164 who succeeded were then asked to adhere to one of three diets, each with a slightly different ratio of fats to carbohydrates. In each case, protein intake was fixed at 20 percent, so a “high”-carbohydrate diet consisted of 60 percent carbs and 20 percent fats, a “moderate”-carbohydrate diet consisted of 40 percent carbs and 40 percent fats, and a “low”-carbohydrate diet consisted of 20 percent carbs and 60 percent fats.
When Ludwig’s team measured resting energy expenditure in these three groups, they found that those who adhered to the low-carbohydrate diets burned more calories at rest than those on the high-carbohydrate diet. When they compared the resting energy expenditures of the lower-carb diets to the high-carb diet, the results showed a clear winner: roughly 209 to 278 more calories per day for those on low-carb diets, versus just 91 more calories per day on moderate-carb diets.
Where this study largely succeeds is in its rigorous design, which has won over some researchers, including Kevin Hall, Ph.D., who studies diet and physical activity at the National Institute of Diabetes and Digestive and Kidney Diseases. Though he also pointed out to the New York Times that he wasn’t completely sold on the method Ludwig’s study used to measure resting energy expenditure. Ludwig disagreed with that characterization:
“We used a gold standard method that has been validated across a wide range of experimental conditions and universally adopted in the field,” he told the The New York Times.
This study is part of a larger case Ludwig has been building that suggests that the real drivers behind obesity in America are refined grains, potato products, and sugars — not high-fat foods. This is based on a hypothesis called the carbohydrate-insulin model, which he describes in his book, numerous op-eds, and several scientific papers that describe how this dynamic may lead to weight gain.
In short, this model suggests that eating carbohydrate-rich meals leads to the overproduction of insulin — a hormone that helps the body store glucose in fat cells. His work suggests that high-carb diets cause these cells to essentially hoard glucose and reduce the amount of a different hormone, called glucagon, which helps our body use up the glucose, leaving the body without an energy source. He believes that this creates a vicious cycle: We feel more hungry and therefore consume more to fill this void.
But it’s important to note that there are still avenues to explore with this model — even Ludwig wrote in the LA Times that this study doesn’t prove the hypothesis entirely, and there are some legitimate criticisms — namely, a lack of strong evidence supporting the carbohydrate-insulin model. Some further avenues of exploration include investigating how eating a high-fat diet affects calorie burning over long periods of time. There was a slight decrease in these burn rates after the 10-week mark in the study — so this high burning rate may not last forever. Inverse has reached out to the authors regarding this question and will update the article if we hear back.
But for now, it’s probably safe to say that this study provides evidence that calories from different sources may have widely differing effects on the body. We may later confirm that they’re not all created equal.