The best path to dieting success may not be the diet you choose. It's whether you can stick to your plan, according to a study that examines four popular diet options.
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While most diet studies examine specific diet plans, Dr. Michael Dansinger of Boston's Tufts-New England Medical Center and colleagues compared the advice given in four popular options: Weight Watchers, which stresses reduced calories; Atkins, which focuses on reduced carb intake; the Zone diet, which stresses glycemic loads and nutritional balance; and the low-fat vegetarian plan devised by Dr. Dean Ornish.
Those who stayed on any of the diets for one year lost more weight, reduced their body mass index and generally improved their cholesterol levels more than the overall group. But the researchers found no major advantage to any one diet, according to results released Tuesday by the Journal of the American Medical Association.
"If one author wants to claim that people can follow his diet better than others, this study does not support that conclusion," Dansinger says.
The scientists randomly assigned 40 people to each diet, gave them copies of books that detail each plan and provided group advice from a dietician and physician during the first two months. The diet regimes were standard for each plan, though Weight Watchers noted its plans often include counseling not provided in the study.
After two months, fewer than 80 percent remained on the diets. At the one-year mark, that dropped to 58 percent. Each group lost similar amounts of weight — slightly under 4 percent of body weight at two months, with 10 percent of each group losing more than 10 percent of their weight at one year. More participants abandoned the Atkins and Ornish diets than the other two.
The study didn't measure metabolic changes, but in each diet, the researchers found that weight loss occurred when dieters reduced the number of calories they consumed. "For all the diets, the more closely you followed the diet, the more you reduced your calories," Dansinger says.
The latest findings come amid a sea of claims and counterclaims by the diet industry, often bolstered by dramatic testimonials. "Robyn lost 26 pounds," boasts the Jenny Craig Web site, with a tiny "results not typical" footnote. Such colorful marketing claims have helped make commercial weight-loss programs a $2.1 billion annual business.
Yet a separate review of published scientific evaluations of popular diet plans, released this week in the Annals of Internal Medicine, found few rigorous studies back up these claims.
Diet studies fall short
The study, conducted by researchers at the University of Pennsylvania, found only one program — Weight Watchers — had enough solid data to show that its participants effectively shed pounds and kept them off. Other studies of diet plans did not track subjects for a long enough period of time, or lacked crucial data, such as the number of original participants who entered the program.
Only Weight Watchers met the criteria set forth by the University of Pennsylvania researchers, who evaluated 108 U.S. studies and settled on 10 that were comprehensive enough for detailed review.
Dieters using Weight Watchers lost over 5 percent of their body weight after six months, and kept off over 3 percent after 2 years.
Results for many weight-loss programs had flaws, and the researchers could not find data for popular programs such as Jenny Craig and LA Weight Loss.
"I hope that patients are smart enough to know that when they go to these programs they're being presented with best-case scenarios of weight loss," Adam Tsai, the study's lead author, told MSNBC.com. "But I don't always know if that happens or not."
Jenny Craig described data compiled by the Cooper Institute in Dallas that showed 15 percent weight loss by dieters who stuck with its program, which requires members to purchase its pre-prepared meals, for a year.
Jenny Craig believes the Cooper results would have been included in the Pennsylvania study but weren't published in time, and noted a two-year study by the University of California at San Diego is under way, with initial results available this spring.
"We really do applaud these types of studies because there's a lot of charlatans in our industry," says Jenny Craig vice president Kent Coykendall.
'A tainted message'
A lack of comprehensive long-term studies has made it difficult for doctors and their patients to assess many diets' merits and risks.
The short-term focus of most diet plans is the problem, says Dr. Robert Eckel, a researcher at the University of Colorado Health Science Center and the president-elect of the American Heart Association.
In an accompanying editorial in this week's Journal of the American Medical Association, Eckel notes that Dansinger's study differs vastly from other studies that tout one diet or another.
He sees the results as an endorsement of healthy long-term behavioral changes, not fad diets.
"I think it's been a tainted message thus far," Eckel told MSNBC.com. "We've got to teach people how to eat right in terms of the quality of their diet first, and then the quantity needs to be modified to account for long-term behavior."
Part of what gets in the way may be money.
Weight loss and dieting were a $40 billion industry in 2002, according to John LaRosa of research firm Marketdata. But LaRosa estimates most Americans only want to spend $500 or less on weight loss, based on data from Bestdietforme.com, a free diet-evaluation service. That modest budget drives people to do-it-yourself solutions like diet books, which may show short-term results but are of questionable benefit in the long run.
More structured diet plans that hold people accountable over the long term may produce better results, says Karen Miller-Kovach, Weight-Watchers chief scientific officer.
"The typical person who comes to Weight Watchers realizes they need a method and they need a structure," she says.
Of the structured diet plans studied, Weight Watchers costs less than most — Tsai and fellow researcher Thomas Wadden estimated $167 for three months. By contrast, Jenny Craig was estimated to cost nearly $1,250 — though Coykendall argues much of that is for its meals and offsets other food costs.
Cost is no indicator of success, either. Medically supervised programs such as Optifast and Health Management Resources were among the most expensive considered by researchers: up to $2,000 or more for the first three months, prohibitive for most people to pursue long-term.
Not surprisingly, many dieters did not stay on the intensive programs and researchers could not find studies that detailed every patient's long-term progress.
"Most of the patients regain a significant amount of weight," Tsai said.
Rather than anoint a winning solution, Dansinger said he hopes his research will prompt doctors and dieticians to think beyond their usual range of nutritional advice and help patients find functional long-term methods. "The notion that one diet fits all is becoming an old-fashioned notion," he said.
Eckel argues the entire means of evaluating diets may be off-target. Not only should we look beyond weight loss, he believes, but indicators like cholesterol levels and blood pressure may not be meaningful unless considered over years, not months.
"Let's see weight loss itself can lessen cancer risk, lessen heart disease risk, lessen stroke," he says. "There's just no good long-term data."
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