February 26, 2009 (Boston, Massachusetts) — It may be one of the most commonsense observations ever to be validated in a diet study: people lose weight if they eat fewer calories, regardless of where those calories come from [1]. That's the upshot of a two-year study by Dr Frank Sacks (Harvard School of Public Health, Boston, MA) and colleagues, published in the February 26, 2009 issue of the New England Journal of Medicine.
After two years, 811 overweight adults randomized to one of four heart-healthy diets, each emphasizing different levels of fat, protein, and carbohydrates, showed similar degrees of weight loss. On average, patients lost 6 kg in six months, but gradually began to regain weight after 12 months, regardless of diet group.
According to Sacks, the research should help quell some of the debate--fostered by decades of research and fad diets--over what types of foods should be emphasized to produce weight loss.
If people can maintain a calorie deficit no matter what type of diet they were on, they're going to lose weight.
"Research has looked at whether carbohydrate is more satiating than fat, or whether protein is more satiating than carbohydrates, or whether overeating fat puts more fat in the belly than overeating carbohydrates, etc," Sacks explained. "So what's concerned colleagues of mine on the nutrition guideline panels in the past is the possibility that if we say that a 40% fat diet is okay, that maybe that would lead to weight gain. But where this study is going to be helpful is in saying 40% fat, 20% fat, it doesn't matter. If people can maintain a calorie deficit no matter what type of diet they were on, they're going to lose weight."
Sacks, who is incoming chair of the AHA's Nutrition Committee, acknowledged that nutrition advice in the past has worried too much about fat in the diet. "I'm very concerned that we maintain the focus on calories and keep the focus off percent calories from fat," he said.
Another important, if unsurprising, finding from the study was that people who regularly attended counseling sessions over the two-year study were significantly more likely to lose weight.
The findings should remind physicians to hammer home the importance of losing weight. "Physicians really should, visit after visit, keep encouraging patients to eat a heart-healthy diet that they can stick with, that will help them lose weight, and try to get them involved in some kind of support group or to see a dietician," Sacks said.
Commenting on the study for heartwire, Dr Robert Eckel (University of Colorado Health Sciences Center, Denver) said he wasn't surprised by the study findings. "I think you can lose weight in a number of different ways, and this study simply affirms that people who are successful are the people who adhere to a program. . . . Ownership, by the patient, of the weight-loss program is what proves successful, not the type of diet you chose."
Diet Details
The diets tested in the study included the same types of foods, but in different proportions, and were tailored to patients such that overall calorie consumption was reduced by approximately 750 calories per day, with each diet including a different macronutrient composition:
- High-fat, average protein: 40% fat, 15% protein, 45% carbohydrate.
- High-fat, high-protein: 40% fat, 25% protein, 35% carbohydrate.
- Low-fat, average protein: 20% fat, 15% protein, 65% carbohydrate.
- Low-fat, high-protein: 20% fat, 25% protein, 55% carbohydrate.
Participants were advised to exercise for at least 90 minutes per week, at a moderate level, and were offered counseling sessions every eight weeks, with group sessions held weekly or biweekly over the course of the study.
In all, 80% of subjects completed the trial, and 14% to 15% of subjects managed to lose at least 10% of their initial body weight. Subjects randomized to different groups reported similar degrees of satisfaction, hunger, and satiety. All the diets reduced risk factors for diabetes and cardiovascular disease at six months and two-year follow-up. At the two-year mark, the low-fat diets and the highest carbohydrate diet fared better than the high-fat diets and low-carb diet in terms of reducing LDL cholesterol. By contrast, the lowest carbohydrate diet improved HDL-cholesterol levels more than the highest carbohydrate diet. All of the diets produced slight improvements in blood pressure and decreased the number of patients with metabolic syndrome. All, with the exception of the highest carbohydrate diet, decreased fasting serum insulin levels.
External and Internal Motivators
An editorial accompanying Sacks et al's study applauds the duration of the study and the low dropout rate but takes a dimmer view of the weight loss achieved in the study and the ability of dieters to adhere to their diets over time [2]. "Even these highly motivated, intelligent participants who were coached by expert professionals could not achieve the weight losses needed to reverse the obesity epidemic," Dr Martijn B Katan (VU University, Amsterdam, the Netherlands) writes. "The results would probably have been worse among poor, uneducated subjects. Evidently, individual treatment is powerless against an environment that offers so many high-calorie foods and labor-saving devices."
Sacks, speaking with heartwire, defended what he insisted was "clinically meaningful" weight loss in his study, emphasizing that many people achieved far greater losses than the average figure. Eckel, by contrast, was less sanguine, pointing out that an average weight loss of 3.5 kg at two years represents the best-case scenario, since real-life interventions rarely live up to the research setting.
Katan, however, argues that "like cholera, obesity may be a problem that cannot be solved by individual persons but that requires community action." He cites a French study that profoundly reduced obesity rates in children by having everyone in the town commit to getting children to eat less and move more, building sporting facilities and playgrounds, giving cooking workshops to families, creating walking itineraries, etc.
"It is an approach that deserves serious investigation, because the only effective alternative that we have at present for halting the obesity epidemic is large-scale gastric surgery," he writes.
In response, Sacks said simply that communitywide changes won't absolve individual responsibility. "It's two factors. There's what each person puts into his or her mouth, and there's what's out there for people to choose to put in their mouths."
- Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med 2009; 360:859-873.
- Katan MB. Weight-loss diets for the prevention and treatment of obesity. N Engl J Med 2009; 360:923-924.