If you go on a low-carbohydrate diet to shed weight, you've probably made a good decision, according to a new report by Stanford University researchers.
Just don't expect miracles.
In the largest head-to-head study of competing diets so far, low-carb plans such as the Atkins Diet turned out to be safe and effective for losing weight and improving cardiovascular health - at least in the short run.
In fact, women who aggressively restricted carbs lost nearly twice as much weight over six months as women on higher-carb diets, the Journal of the American Medical Association reported today.
After a year, the low-carb dieters also saw greater improvement in cardiovascular disease risk factors - such as blood pressure and cholesterol.
The bad news: Even those on the Atkins plan, which outscored three competing diets, were down only 10 pounds after a year. And on every plan, by the end of the study, most dieters were slowly but surely regaining the weight they had lost.
"It shows that people will steadily go back to their old habits," said Dr. Lawrence J. Cheskin, director of the Johns Hopkins Weight Management Center. "After two years, you might find that everybody has regained everything."
Still, researchers welcomed the news that popular low-carb diets are safe and effective - if not a panacea for obesity.
"There is increasingly some evidence that in the short term you might be able to lose more weight on a low-carbohydrate, high-protein diet," Cheskin said.
Christopher D. Gardner, a professor of medicine at Stanford and the lead author on the study, also cautioned that the long-term safety of low-carb, high-protein diets is still in question.
"We don't know what a high-protein diet would do over 10 years," he said. "It could impair kidney function or leach calcium out of the bones. But we didn't look at that."
The study is the largest yet to explore the difference between popular diets and was intended to scientifically address concerns about low-carbohydrate plans. "We haven't had a lot of data on these diets," Gardner said.
The researchers studied four diets representing a range of recommended carbohydrate consumption.
Three of the diets - Atkins, Zone and Ornish - were created by individual doctors and popularized in books. The fourth was based on federal dietary guidelines and dubbed LEARN, for Lifestyle, Exercise, Attitudes, Relationships and Nutrition.
The Atkins Diet, popularized by the late Dr. Robert C. Atkins, calls for the fewest carbohydrates and lots of protein. At the other end of the carb spectrum was the Ornish diet, developed by Dr. Dean Ornish, a cardiologist at the University of California. It focuses on cutting fat intake.
Yesterday, Ornish questioned the validity of the researchers' conclusions, arguing that the study participants weren't adhering to the four diets strictly toward the end of the study.
"People didn't really follow the diet I recommend," he said. "What [the researchers] really found was that if you give people a book and a few classes with a dietitian, they won't follow the diet very well."
The study tracked the weight of 313 overweight or obese women for one year beginning in February 2003. The women were 25 to 50 years old and lived in the community surrounding Stanford's campus near Palo Alto, Calif.
Randomly assigned to one of the diets, each volunteer received the appropriate book and the opportunity to attend eight classes explaining the diet. The women were also encouraged to exercise regularly.
Once the classes finished, the women were on their own to follow their assigned diets and prepare or buy their own food - just as they might in real life.
After six months, women on the Atkins diet had lost an average of about 13 pounds. Next highest were the women on the LEARN diet - a low-fat plan based federal guidelines. They dropped about 7 pounds on average.
The women on the Atkins diet also saw greater improvement in blood pressure and levels of high-density lipoprotein (HDL), often referred to as "good" cholesterol.
On the other hand, the low-carb dieter's levels of "bad" cholesterol levels - low density lipoprotein (LDL) - increased during the first couple of months.
Dr. Denise E. Bruner, a bariatric physician from Arlington, Va., who prescribes low-carb diets for her patients, said an initial rise in bad cholesterol is normal. "As the lipids are being metabolized," she said, "there is often a bump in the HDL levels."
There was no significant difference in HDL among the diets after a year.
Although none of the diets produced dramatic, lasting weight loss, Gardner said several factors might explain why the Atkins plan was somewhat more effective.
One, he said, is that Atkins calls for drinking lots of water - eight 8-ounce glasses a day. That reduced the quantity of soft drinks and other sweetened beverages the women drank.
The diet also calls for protein-rich meals, which might have cut down on consumption of refined carbohydrates such white flour. Protein-rich foods are also more filling, Gardner said, so people who eat them tend to take in fewer calories overall.
Pamela Waltos, 46, of Bowie, said she has not felt hungry since she went on Atkins at the beginning of the year.
"You're eating whole foods, proteins and vegetables that keep you fuller longer," she said. "I have to remind myself to eat."
She started the diet weighing 242 pounds and has lost 22 pounds.
Another explanation for rapid weight loss is the Atkins diet's simplicity, experts said. "It doesn't have very many rules," said Gardner.
He said that might account for the observation that after a year, the women on Atkins were adhering to their diets a little more closely than women on the other plans. In all four groups, however, the women's weight had begun to creep back up after a year.
Robin L. Spence, a dietitian at Union Memorial Hospital, said other research has shown similar trends.
"In all the studies, you see much greater weight loss at the beginning," she said. "What we really want to know is where are the [dieters] in three years."
The research, she said, might suggest that dieters should choose low-carb plans initially and switch to less "extreme" diets later on.
"I have always been a proponent of gradual change," she said, " but the weight loss can be so minor that people say, 'What's the point?'"
She added that different diets can work for different people - a theory supported by the Stanford study. A few women on each of the four diets lost more than 40 pounds and kept it off for the duration of the study.
"If you look at the way people lose weight, it's every kind of way in the world," Spence said. "It shows that if somebody is motivated, patient and consistent, they are going to lose."