A new study suggests low-carb diets may not be as effective for weight loss as popular culture believes.
The study, led by National Institutes of Health obesity researcher Kevin Hall, attempted to test whether a diet low in carbs, with its resulting drop in insulin, would lead to the loss of fat that proponents of low-carb diets, like Atkins suggest, reports Vox. The researchers found the results were not as dramatic as those diets might claim.
The theory behind low-carb diets, called the "carbohydrate-insulin hypothesis," suggests that a diet that is heavy on carbohydrates leads to an increase in weight because carbs increase the body's supply of insulin, which in turn leads the body to hold on to more fat and burn fewer calories.
Low-carb diets, in turn, recommend replacing calories from carbohydrates with calories from fat to drive down insulin levels, which is purported to have the opposite effect on weight.
One of the reasons scientists have found this theory hard to prove is the difficulty that study subjects have sticking to an assigned diet for a long period of time. Many studies of low-carb diets have ended up flawed as a result of this and other factors, such as a reliance on observational studies rather than randomized trials.
The new study kept 17 patients who were healthy, but obese or overweight, in a hospital for two months, keeping careful track of the patients' movement and energy expenditure, along with their diets, according to Longevity magazine.
For the first month of the study, the subjects were given a baseline diet similar to what they had said they were eating before the study began, including, in many cases, a large amount of carbohydrates. In the study's second month, the participants were given a diet consisting of the same number of calories and protein as their baseline diet, but with a sharp reduction in carbs, replaced by calories from fat to lower insulin levels.
For example, during the first month, a participant may have eaten a cheesesteak sandwich for dinner, while in the second month, they might have a hamburger patty, without a bun, over a bed of sauteed squash and mushrooms.
Hall said the results showed the difference from the insulin drop was much less dramatic than expected. The increase in calorie burn, for example, which low-carb diets say can range from 300-600 calories a day, was closer to 100 calories a day.
"These studies represent the first rigorous scientific tests of the carb-insulin model in humans," said Hall. "The public needs to understand that this [insulin-carbohydrate] model now has pretty strong evidence against it."