Low-carbohydrate diet may help maintain weight loss, study says
In integrative medicine, it has long been understood that calories are not the only factor that count when it comes to losing weight and eating healthfully, but rather dietary composition and quality. Now, a new in-depth study published last week in the journal BMJ backs up this line of thinking.
Researchers found that overweight adults who cut carbohydrates and replaced them with healthy fat increased their metabolism. After five months, their bodies burned roughly 250 calories more per day that those who ate a high-carbohydrate and low-fat diet. The results suggest that restricting carbohydrate intake in favor of a high-fat diet could help people lose and maintain weight more easily.
In this randomized controlled trial with a controlled feeding protocol, researchers looked at adults age 18 to 65 years old with a body mass index of 25 or higher and body weight less than 350 pounds. The trial was broken in to run-in and test phases. During the run-in phase, calorie intake was restricted to promote 12 percent weight loss over nine to 10 weeks. Researchers randomly assigned participants who achieved the target weight loss to a high, moderate, or low carbohydrate diet for the 20-week test phase.
The study was conducted at Framingham State University in Massachusetts, where assessments and weigh-ins took place. For implementing controlled feeding protocols with free living participants, researchers established a partnership with Sodexo, the food service contractor at Framingham State University.
During the test phase, participants’ calorie intake was adjusted periodically to maintain weight loss within about four pounds of the weight loss achieved in the run-in phase. Participants were asked to weigh themselves daily using a calibrated Wi-Fi scale during both phases, and study outcomes were accessed pre-weight loss, at the start of the trial, eight to 10 weeks in to the test phase, and at the end of the test phase.
The macronutrient composition of the run-in diet, based on ranges considered acceptable by the Institute of Medicine, was 45 percent calories from carbohydrates, 30 percent from fat, and 25 percent from protein. Individual caloric needs were determined using a regression equation and multiplied by a physical activity factor of 1.5, which corresponds to a light activity lifestyle. Calorie intake was restricted to 60 percent of the estimated needs and was monitored and adjusted when necessary to achieve the target weight loss. At the end of the run-in phase, researchers adjusted calorie intake to stabilize body weight.
For the test phase, high, moderate, and low carbohydrate diets varied in carbohydrate (60 percent, 40 percent, and 20 percent of total energy, respectively) and fat (20 percent, 40 percent, and 60 percent, respectively), with protein fixed at 20 percent of daily caloric intake. The relative amounts of added sugar (15 percent of total carbohydrates), saturated fat (35 percent of total fat), and sodium (3,000 milligrams per 2,000 calories) were held constant across diets.
From the run-in phase, 54 participants were assigned a high carbohydrate diet, and 16 did not achieve weight loss maintenance. Of those assigned a moderate and low carbohydrate diet (53 and 57, respectively), 13 from each group did not achieve weight-loss maintenance. However, when analyzing resting energy expenditure and physical activity, the low carbohydrate group burned more calories overall, meaning metabolism was more efficient.
The results go back to the core of the diet debate: are calories paramount for optimal weight loss? While weight loss was achieved across the spectrum of dietary compositions, when it comes to building a metabolism that can work efficiently with less effort by the patient, the low-carbohydrate, high-fat diet reins supreme.