What's the best way to lose weight - load up on proteins and cut carbohydrates? Keep the good carbs and just trim fats? Or build "healthful" fats into your diet?
Scientists now say it doesn't matter as long as you consume fewer calories.
A new study in The New England Journal of Medicine tested four different diets and found that participants lost similar amounts of weight on each of them.
In the extensive two-year study, investigators randomly assigned more than 800 overweight participants to follow one of four heart-healthy diets, each emphasizing a different combination of carbohydrates, protein and fat.
All replaced saturated with unsaturated fat and emphasized whole grains, fruits and vegetables. But a diet that stressed protein, for instance, included more servings of lean fish and chicken, while a diet higher in fat included more olive oil.
All the regimens had similar calories.
Regardless of diet, participants tended to lose the same amount of weight. At six months, they had lost an average of 13 pounds, and they maintained a 9-pound reduction after two years.
"On average, no one diet is better than another for weight loss," said Dr. Frank M. Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health and lead author of the study.
"The determining factor ended up being calories," he said. "It really comes down to people doing what is most effective for themselves, as long as [the diets] are healthy and prevent heart disease."
The investigation was a joint effort by researchers from Harvard; the Pennington Biomedical Research Center at the University of Louisiana, Baton Rouge; and the National Heart Lung and Blood Institute, a division of the National Institutes of Health.
Local weight loss experts called the findings significant and said they confirm a common-sense approach to weight loss.
"It is very commendable," said Dr. Soren Snitker, assistant professor at the University of Maryland School of Medicine. "I agree with them that we should not get hung up on fat, carbohydrate and protein contents. But this is about producing a diet that is palatable and culturally relevant to the patient. There are actually several ways of getting to your goal."
Nevertheless, this is not the diet study to end all others, said Dr. Lawrence J. Cheskin, director of the Johns Hopkins Weight Management Center.
While it might be true that a calorie from fat is the same as a calorie from protein or carbohydrate, Cheskin said, certain weight-loss techniques seem to work better than others. In his experience, the most successful diet is high-protein and low-carb and involves meal replacement, such as using ready-made, portion-controlled dinners or protein shakes for lunch.
"I have noticed that people who are on high-protein, low-carb diets have a better time adhering to that diet," he said. "They're less hungry, for example."
The study had other drawbacks. For instance, only about a third of people actually adhered to their diet. And participants gained some of their weight back in the second year. While the weight gain was slow, the trend could suggest that participants would be likely to gain back some of their weight even if they had continued treatment, said an accompanying editorial in the journal.
Weight-loss experts agree that motivation, encouragement and counseling can make a difference as to whether a person sticks with a diet. Study participants took part in group and individual counseling sessions, recorded what they ate in a daily food diary and used a Web-based program that encouraged them to meet their goals.
"It matters more that you are motivated and adhere to it," said Cheskin. "It's not that diets don't work, but diets don't work if you don't adhere to them."
Ralph Loglisci of Baltimore can attest to that. A lifelong dieter, he had tried them all: motivational tapes, self-help books, Overeaters Anonymous, Weight Watchers and even gimmicky color-coded menus popularized by the 1980s fitness guru Richard Simmons. Loglisci would lose a few pounds, only to gain them right back.
In 2003, he was 32 years old, weighed 383 pounds and couldn't go for a walk in his neighborhood without his back aching.
"I was one accident away from becoming one of those stories about people stuck in bed and needing to be taken out with a forklift," he said. "This was the fear in my head - it was horrible."
Loglisci sought help at the Hopkins Weight Management Center, which he says changed his outlook on food, dieting and health. He received behavior therapy and learned why he relied on food for comfort. He also received nutrition and medical advice and tips for controlling portion sizes, especially during the first few months. In nine months, he lost 185 pounds.
He learned that no matter what he ate, when he reduced his calories, he lost weight.
"I am not sitting around counting calories," said Loglisci, who weighs about 230 pounds today and went public with his weight loss journey on WBAL-TV, where he used to be a producer. "But I don't drink regular soda. Every time I eat a cracker or a cookie, I'm conscious of it. You have to realize that everything you put in your mouth matters that day."
Snitker said the key to any diet is that a patient believes in it. A decade ago, dieters praised the Atkins high-protein, low-carb diet and it became all the rage. But it didn't work for everyone.
"You couldn't go to a restaurant or a grocery store without someone offering you low-carb this and low-carb that," he said. "I know a lot of people who told me how wonderful that diet was. But people might have been caught by the enthusiasm for that diet."
A strength of this study is that it removed the dieting labels - such as South Beach, Zone and Mediterranean - to help participants focus on losing weight, rather than following a trend.
Snitker said this research should spur a study that examines how to determine the best diet for a particular person. Too many dieters are quick to dive into the latest craze, sometimes eating food they don't even like.
"What I would like to see, instead of being guided by the newest fad, is for people to sit down with a dietitian and look at ways they can shave off calories in their diet," he said.
Catherine Loria, a nutritional epidemiologist at the National Heart Lung and Blood Institute, said she discourages dieting. Rather, she advises people to adopt healthy eating patterns they can maintain for the long term.
"It's a lifestyle change," she said.
* 811 people were randomly assigned to one of four diets: low fat/average protein; low fat/high protein; high fat/average protein; high fat/high protein.
* For all four diets, participants were to eat 750 calories a day less than their baseline. They also had to exercise 90 minutes a week.
* Two years later, 645 people were still in the study. Regardless of diet, their success rates were similar:
* 31 percent to 37 percent lost at least 5 percent of their initial weight
* 14 percent to15 percent lost at least 10 percent
* 2 percent to 4 percent lost 44 pounds or more.