Harvard Public Health Review
Fall 2004

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Dueling Diets

An HSPH study asks: How best to lose weight--and keep it off?

Go to any cocktail party, play group, or breakroom in America, and you're bound to hear about the low-carb miracle. Suddenly, low-fat is old hat--and the newly thin are boasting of how they lost ten, 20, or 30 pounds on the Atkins plan while dining freely on cheese, butter, and steak.

But check in with these fad dieters in six to 12 months, and most of the pounds are bound to have come back. Meanwhile, many have been raising their risk of heart disease by consuming foods laden with saturated fat.

Now HSPH researchers have launched a study to ask: How should people eat if they want to keep excess weight off--and do it in a healthy way? With funding from the National Institutes of Health, Frank Sacks and colleagues will be the first to compare the long-term success of four eating regimens featuring varying percentages of fats, carbohydrates, and proteins. Unlike most other previous weight-loss trials, which followed people for just six, eight, or 12 months, this study will track dieters for two years. The goal is to find an eating plan people will follow for life, not just a few tortured months.

"The question really is: How do these diets differ in the long run? That's what we care about. That's what's related to health," says Sacks, a member of the HSPH Department of Nutrition. "Weight loss at six months--that's meaningless."

FOUR REGIMENS

The low-carb route promises quick weight loss and, for many, it delivers. It even comes with what some researchers say is a scientifically sound justification: Many carbohydrates cause a spike in blood sugar, or glucose, followed by a sudden drop that triggers hunger pangs. By severely cutting back on carbs, dieters can take advantage of a process called ketosis, in which the body burns fat instead of glucose for fuel.

"The problem with extreme diets--low-carb, low-fat--is that people don't stick with them," Sacks says. "It's hard to eat in a restricted way for long. And any diet that isn't palatable or appealing, or doesn't meet the body's needs, is not a good public health strategy."

Such diets do shed pounds, says Sacks, who has studied both vegetarian and low-fat strategies. But research consistently shows that by month six or eight, people lose as much as they are going to, he says. Then, over the next year or two, they typically regain some or all of that weight.

The HSPH study, which will begin enrolling 800 overweight and obese men and women in September, will look at what happens to dieters divided into four groups, each of which emphasizes certain nutritional components more heavily than others (see charts on page 18). Researchers will not only tally pounds shed. They will also monitor key health indicators, such as cholesterol and blood pressure levels, as well as mental health, to see how participants are feeling overall. In so doing, investigators aim to cut through the anecdotes and piecemeal science of weight loss with hard data and long-term results.

"Potentially, this could be a landmark study," says Kathy McManus, a co-investigator who is the director of nutrition for Brigham and Women's Hospital in Boston. "We feel strongly that this study needs to be done because people are so confused." Many are wondering what became of the low-fat mantra (see sidebar at right).

MEDITERRANEAN STYLE

For Sacks and McManus, the idea for this new study came in a roundabout way. Neither is an obesity researcher. Sacks, trained as a cardiologist, has studied lipoprotein metabolism through clinical trials focused on heart disease and nutrition. He works with McManus in the Brigham and Women's Lipids Clinic, and it was there that they began prescribing a moderate-fat diet for patients with high cholesterol.

Rather than outlaw all fats, this diet--known as the Mediterranean diet--emphasizes plant-derived fats like olive oil and oils in nuts. It also minimizes saturated fats by emphasizing fish and poultry over red meats as protein choices. Mediterranean-style diets had been known since the 1970s to improve cholesterol levels. To their surprise, however, McManus and Sacks discovered that many of their patients not only lowered their "bad" low-density lipoprotein (LDL) cholesterol, but also lost weight and kept it off.

"After we had a number of very exciting successes," says McManus, "we decided to do a study."
They put about 50 patients on the Mediterranean-style diet, and another 50 on a traditional low-fat plan. After six months, both groups lost an average of 11 pounds. Then, participants started dropping out. After 18 months, only 20 percent from the low-fat group had stuck with their diet, compared to 54 percent from the Mediterranean group. On the whole, patients assigned to the low-fat arm gained an average of 6.4 pounds, while those in the Mediterranean arm lost 9 pounds.

"What patients in the Mediter-ranean group told us was that they didn't feel like they were dieting," Sacks says. "They could choose a lot of different foods. They could fry things, put olive oil on their salad. They felt they could eat more of a normal diet."

Just as Americans began picking up on the low-carbohydrate approach, Sacks began lobbying the National Heart, Lung, and Blood Institute for funds to do a long-term study comparing the Mediterranean diet to other popular eating plans. Now he, McManus, and their partners at Louisiana State University (LSU) are recruiting participants in both Boston and Baton Rouge. The latter site, at LSU's Pennington Biomedical Research Center, will be supervised by George Bray, an expert on diet and diabetes prevention who has long advocated a low-fat, high-carbohydrate approach to weight loss.

DIETARY PRESCRIPTIONS

Unlike some other clinical trials, weight-loss studies have no trouble attracting participants. This time, however, researchers need people who have a reasonable chance of sticking with an eating plan. Potential subjects who respond to ads in local newspapers are put through several qualifying visits. During an hour-long interview, a dietician will assess their commitment. Those selected will be assigned randomly to one of four groups.

Rather than supply food, the researchers will "prescribe" menus for three meals a day, each specifying a certain percentage of protein, carbohydrate, and fat content. Participants must attend group meetings weekly for the first six months, and every two weeks after that. In Boston, study subjects will gather at a facility that features classrooms and a kitchen for cooking demonstrations.

Exercise will be a component of all four weight-loss plans. Participants who don't already exercise must take up walking or some other form of physical activity, starting with 30 minutes per week and increasing to 90 within five months. Exercise goals are set low to make sure energy expenditures don't obscure the weight-loss impact of their diets. But people who want to exercise more won't be discouraged.

For most people, "exercise and careful food choices are essential to maintaining a healthy weight in the long run," notes HSPH Department of Nutrition Chair Walter Willett, who has published extensively on the dietary habits of thousands of people through the Nurses' and Health Professionals' studies. This new trial, he says, should identify a way of eating that people can live with--"one that's enjoyable, has variety, and is compatible with living in the 21st century."
For details about the weight-loss trial, visit the HSPH website this fall: www.hsph.harvard.edu/nutritionsource/.

Tinker Ready is a freelance health and medical writer based in Cambridge, Mass.

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