Two decades after the debate began on which diet is best for weight loss, a conclusion is starting to come into focus. And the winner is — not low-carb, not low-fat, not high protein, but — any diet.
That is, any diet that is low in calories and saturated fats and high in whole grains, fruits and vegetables — and that an individual can stick with — is a reasonable choice for people who need to lose weight. That’s the conclusion of a study published Wednesday in the New England Journal of Medicine, representing the longest, largest and most rigorous test of several popular diet strategies.
In light of another highly regarded study published last year that reached a similar conclusion, medical experts are embracing the back-to-basics idea that the simple act of cutting calories is most important when it comes to losing weight.
The conclusions could end the often-contentious debate over the comparative effectiveness of diets that are predominantly low in fat, high in protein, low in carbohydrates or marked by other specific configurations of nutrients.
“This study is saying it doesn’t make any difference what diet you choose. Calories have always been the bottom line,” said Dr. Robert Eckel, a physiology professor at the University of Colorado Health Sciences Center and past president of the American Heart Association.
The findings should free people from the notion that it’s necessary to eat a specific ratio of fat, protein and carbohydrates. They should choose, instead, what works for them. “There isn’t any one way. That is the nice thing about none of these diets in particular winning,” said Christopher Gardner, a nutrition researcher at Stanford University’s Prevention Research Center. “We don’t have any right to push low-fat or low-carb or high-protein. If one of these approaches is more satiating, where you will not be hungry and have cravings, that is the one that will work for you.”
The study did not prove, however, that every dieter succeeds. Instead it reinforces numerous other studies showing most people lose a modest amount of weight in the first few months of dieting and regain some or all of the weight over time. In today’s study, the average weight loss was 13 pounds at six months and 9 pounds at two years.
The research followed 811 overweight or obese people, 62 percent of whom were women, enrolled at one of two study sites: Harvard School of Public Health in Boston or the Pennington Biomedical Research Center of Louisiana State University in Baton Rouge. The participants were assigned to one of four diets: low-fat, average-protein; low-fat, high-protein; high-fat, average-protein; and high-fat, high-protein.
The diets ranged from 1,200 to 2,400 calories per day based on each individual’s body mass index and gender, but everyone was asked to cut about 750 calories a day from what they normally ate. All the diets were low in saturated fat, the kind linked to heart disease and found in many fried or processed foods. Participants were asked to do 90 minutes a week of moderate exercise.
They kept a food diary, and a Web-based program provided feedback on how closely they met their goals. Individual and group counseling sessions were held over the two years.
“We were trying to focus on just those three nutrients — fat, protein and carbohydrates — and keep everything else, such as saturated fat and fiber, as consistent as possible,” said Catherine M. Loria, project scientist at the National Heart, Lung and Blood Institute, which funded the research. “This shows people can just focus on counting calories. They have a lot of flexibility. It’s a great finding.”
The study refutes the notion that any one nutrient has a special power to accelerate weight loss, said Dr. Frank M. Sacks, lead author of the study and a professor of cardiovascular disease prevention at Harvard University. “We used to think there could be a biological effect of certain diets. That is probably not true.”
There might be a strong behavioral effect in the success of a diet, however. The people who attended two-thirds or more of the counseling sessions over the two years lost an average of 22 pounds compared with the average loss of nine pounds.