Dieting Doesn't Work
UCLA researchers find that people who lose weight usually gain it all back — plus some.
Published Apr 4, 2007 3:58 PM
If dieting doesn't work, what does?
"Eating in moderation is a good idea for everybody, and so is regular exercise," Mann said. "That is not what we looked at in this study. Exercise may well be the key factor leading to sustained weight loss. Studies consistently find that people who reported the most exercise also had the most weight loss."
Diet studies of less than two years are too short to show whether dieters have regained the weight they lost, Mann said.
"Even when you follow dieters four years, they're still regaining weight," she said.
One study of dieting obese patients followed them for varying lengths of time. Among those who were followed for fewer than two years, 23 percent gained back more weight than they had lost, while of those who were followed for at least two years, 83 percent gained back more weight than they had lost, Mann said. One study found that 50 percent of dieters weighed more than 11 pounds over their starting weight five years after the diet, she said.
Evidence suggests that repeatedly losing and gaining weight is linked to cardiovascular disease, stroke, diabetes and altered immune function. Mann and Tomiyama recommend that more research be conducted on the health effects of losing and gaining weight, noting that scientists do not fully understand how such weight cycling leads to adverse health effects.
Mann notes that her mother has tried different diets, and has not succeeded in keeping the weight off. "My mother has been on diets and says what we are saying is obvious," she said.
While the researchers analyzed 31 dieting studies, they have not evaluated specific diets.
Obesity an illness
Medicare raised the issue of whether obesity is an illness, deleting the words "Obesity is not considered an illness" from its coverage regulations in 2004. The move may open the door for Medicare to consider funding treatments for obesity, Mann noted.
"Diets are not effective in treating obesity," said Mann. "We are recommending that Medicare should not fund weight-loss programs as a treatment for obesity. The benefits of dieting are too small and the potential harm is too large for dieting to be recommended as a safe, effective treatment for obesity."
From 1980 to 2000, the percentage of Americans who were obese more than doubled, from 15 percent to 31 percent of the population, Mann noted.
A social psychologist, Mann, taught a UCLA graduate seminar on the psychology of eating four years ago. She and her students continued the research when the course ended. Mann's co-authors are Erika Westling, Ann-Marie Lew, Barbra Samuels and Jason Chatman.
"We asked what evidence is there that dieting works in the long term, and found that the evidence shows the opposite" Tomiyama said.
The research was partially supported by the National Institute of Mental Health.
In future research, Mann is interested in studying whether a combination of diet and exercise is more effective than exercise alone.
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