Low-Fat Diets Beat Low-Carb Regimen Long Term

MONDAY March 1, 2010 -- Three years after going on a diet, obese men and women on low-carbohydrate "Atkins"-type plans had gained back nearly all their weight, while those on low-fat diets continued to lose, new research finds.

Neither group ended up model-thin, however: Three years out, the low-carb dieters were a mere five pounds thinner and the low-fat group about 10 pounds slimmer than when they began.

The study is published in the March 2 issue of the Annals of Internal Medicine.

In 2003, around the time the low-carb Atkins diet was all the rage, researchers from the University of Pennsylvania published research that found that obese men and women lost a lot more weight -- initially -- when on a low-carb versus a low-fat diet. At the six-month mark, obese dieters on the low-carb plan had lost about 13 pounds, compared to about 4.5 pounds on a low-fat diet.

But what about keeping the weight off long-term? The new study suggests that as time goes on, low-carbohydrate regimens fall short.

The study participants were all severely obese, with a mean body mass index of 43 (30 and above is considered obese) and a mean weight of 288 pounds. About 39 percent had diabetes and 43 percent had metabolic syndrome, a constellation of symptoms that can be a precursor to coronary artery disease and diabetes.

Participants were told to follow either a low-fat diet, in which they cut about 500 calories a day and ate no more than 30 percent of their calories from fat; or a diet that closely matched the low-carb Atkins diet. Low-carb dieters were not told to cut calories, but were instead told to limit their carb intake to no more than 30 grams a day, roughly the equivalent of two slices of bread.

Participants met once a month with a nutritionist for a year. After that, they were on their own to continue the diet or go back to eating as they once did.

After three years, neither group showed a statistically significant difference in their ability to keep the weight off. The good news for those in the low-fat group, however, was that they continued to show slow and steady weight loss, while the low-carb dieters were trending back up.

"It's really hard for people to sustain a low-carb diet. They can stick with it for six months, but then you see a gradual return to baseline," said lead study author Dr. Marion Vetter, medical director of the Center for Weight and Eating Disorders at the University of Pennsylvania. "Low-fat diets may be a little easier for people to stick with."

The researchers also found no changes in blood levels of hemoglobin A1c, a measure of blood sugar control, between the two groups at 36 months.

For the millions of Americans struggling to lose weight, the study highlights the difficulty of sustaining weight loss over the long term no matter what method you choose, Vetter said. Over time, both groups showed a gradual return to their pre-diet caloric intake and eating habits.

Yet there are dieters who are successful in the long term, said Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas. What they tend to have in common is that they cut calories by making small but sustainable changes to their diet and thereby lose weight more slowly.

In the study, those who lost the most at the outset were more likely to gain the weight back, she noted.

"The study further confirms rapid weight loss leads to rapid regains," Sandon said. "When you attempt to achieve weight loss by doing it in a slower manner, you're more likely to keep it off."

In low-fat diets, no food groups are banned, but dieters are encouraged to make certain changes, such as switching from mayo to mustard or from whole to skim milk.

Low-carb diets, on the other hand, require more wholesale changes in the way people typically eat and enjoy food. Realistically, how long can a person put up with asking for their hamburger without the bun?

"People for years have been trying to figure out if it's the carbs or is it the fat, when really it's the calories," Sandon said. "It doesn't matter where the calories are coming from -- carbs, protein or fat -- it's the calorie balance. We're trying to get people away from the idea that it's a single food group or a single nutrient that's causing the weight gain."

More information

Find out more about reining in obesity at the U.S. Centers for Disease Control and Prevention.

Posted: March 2010


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