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 for a lifetime -- is a reasonable choice for people who need to lose weight. That's the conclusion of a study published online Wednesday by the New England Journal of Medicine, research that represents 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 finally 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 Assn.
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 it over time. In Wednesday'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% 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 a 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 close they had come to their goals. Individual and group counseling sessions were held over the two-year study.
"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. "We used to think there could be a biological effect of certain diets. That is probably not true."
There may 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 9 pounds.
The study was highly anticipated because previous research on diets over the last two decades has come to dramatically different conclusions.
"Some studies showed a very low-fat, strict vegetarian diet was best," Sacks said. "Others had Atkins diets doing better. So the question we had was, how do we reconcile all that?"
Many of the previous studies lasted six months or less, enrolled small numbers of people (usually women) and sometimes involved feeding participants prepared meals instead of allowing them to follow the diet on their own in real-life conditions, Gardner said.
Some studies also attracted media attention and marketing hype that may have contributed to the success of specific regimens, Sacks said.
"In this study, we wanted to neutralize these diets," he said. "No marketing. No expectations. All the diets were healthy. We told the participants that experts are completely at odds about which would be better. I think that is a lot of the reason why our study showed they were equal."
Another study, published in July in the New England Journal of Medicine, found that both the Atkins and Mediterranean diets were somewhat more effective than a low-fat diet.
But that study's authors also recommended choosing a diet "according to individual preferences."
Few of the people in the current study strictly adhered to the calorie limits and the composition of their diets, suggesting it is just too difficult to do so, Gardner said. For example, those assigned to consume 35% of their calories as carbohydrates actually consumed an average of 43%, and groups that were supposed to eat a 20%-fat diet averaged 26%. In the end, many of the participants were eating diets that were more similar than dissimilar.
"If the diets are blurring together, then one might expect that the results would be similar," Gardner said. "In reality, trying to follow a low-fat or high-protein diet really has a negative impact on adherence."
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Pounds lost, on average, after six months of dieting.
Average pounds lost after two years of dieting.
Source: New England Journal of Medicine