Many commercial diets claim to have the perfect recipe of fat, protein and carbohydrate to make anybody lose weight. Some argue a low-carbohydrate, high-protein mix is the best pound-dropper. Others say it is just the opposite. Yet scientific proof of these claims is often limited and contradictory.
Now, a team of Harvard researchers has found it really does not matter.
Obese and overweight people experienced similar weight loss despite being on different diets with diverse rations of fat, protein and carbohydrate during a two-year trial led by Harvard researchers in Boston and researchers in Baton Rouge, Louisiana.
The study shows weight loss depends on cutting calories rather than on any specific diet, said Frank Sacks, HSPH professor of cardiovascular disease prevention and senior author of the study. “People can lose weight eating the food they like to eat just by eating less,” he said. “It’s totally logical.”
“This is a definitive study,” said Barbara Howard, who headed an independent National Institutes of Health board that supervised data and safety during the trial. “From the scientific point of view, it settles the issue,” she said.
A total of 811 obese and overweight people who were willing to lose weight took part in the trial, known as Pounds Lost. They were assigned to one of four different diets with various shares of fat, protein and carbohydrate, but all of them were supposed to shave 750 calories per day off their usual menus.
Two years later, participants lost an average of 4 kg (or 8.8 lbs). Weight loss remained similar among those on a high versus average protein diet (3.6 versus 3.0 kg), high- versus low-fat diet (3.3 kg for both), and high- versus low-carbohydrate diet (2.9 versus 3.4 kg).
The levels of cholesterol, triglycerides and insulin, which are major drivers of diabetes and heart disease, went down in all groups. “Those are very healthy changes,” said Sacks.
This two-year study was designed to overcome limitations of previous trials. A common one is that no matter how spectacular the weight loss is for a specific diet in a trial, participants tend to gain weight back after six months. Yet many studies fail to follow participants long enough.
Other problems are small sample sizes, lack of data on the participants’ adherence to the diet, and the researchers’ enthusiasm about a particular weight loss strategy. “A lot of studies are affected by hype,” said Sacks.
Sacks’s team experienced some of these problems as well. Participants took the most weight off after six months, but all groups started regaining it after the first year. Participants also reported going over their assigned calorie intake, said co-author Katherine McManus, director of the Department of Nutrition at Brigham and Women’s Hospital. But unlike other teams, the researchers included all these results in the study, published in the Feb. 26 New England Journal of Medicine.
The researchers also tried to avoid the “hype factor” by ensuring there were no favorites. Participants at the two study sites—HSPH and BWH, in Boston, and the Pennington Biomedical Research Center of Louisiana State University, in Baton Rouge—were assigned to diet groups randomly. Additionally, all four groups enjoyed similar sessions with the teams’ nutritionists. The specialists provided participants with group and individual support and tips on cooking, choosing the right kind of food, and getting back on track after a weekend of indulgence, said McManus.
“We gave each of the diets an equal chance to be the winner, and you might say, they are all winners,” said Sacks. “I think it’s a really optimistic message.”
Students may contact Frank Sacks at fsacks@hsph.harvard.edu for more information.
Conflict Disclosure: The authors declare no conflicts of interest.
Funding Sources: The National Heart, Lung, and Blood Institute of the National Institutes of Health and the NIH General Clinical Research Center
