Weight Loss Program Information Center

ST. LOUIS -- In the first multicenter trial to look at the high-fat, low-carbohydrate Atkins’ diet, researchers have found that at three and six months, the Atkins’ diet produces significantly greater weight loss than a conventional low-fat, high-carbohydrate diet.

All study subjects had medically significant obesity, meaning that they weighed at least 20 percent more than their ideal body weight. They began the study an average of about 50 pounds overweight.

Atkins’ dieters lost twice as much weight during the first six months of the study. However, over the next six months, dieters on both plans tended to regain weight, and there was no statistical weight difference between the groups at one year.

The study also found that people on the Atkins’ diet had greater improvements in blood lipids than those on the conventional diet. High-density lipoprotein (HDL), or “good” cholesterol, increased more in the Atkins’ group, and their serum triglycerides decreased more than conventional dieters. Low HDL and high triglyceride levels increase risk of cardiovascular disease.

The study was conducted by researchers from Washington University School of Medicine in St. Louis, the University of Pennsylvania School of Medicine in Philadelphia and the University of Colorado Health Sciences Center in Denver. The results appear in the May 22 issue of The New England Journal of Medicine.

“This study demonstrates that a low-carbohydrate diet can have beneficial effects in treating obesity,” says senior investigator Samuel Klein, M.D., the Danforth Professor of Medicine and Nutritional Science and director of the Division of Geriatrics and Nutrition at Washington University School of Medicine. “Additional research is needed to understand why subjects assigned to a low-carbohydrate diet lost more weight than those assigned to a conventional diet and to evaluate the long-term efficacy and safety of low-carbohydrate diet therapy.”

The researchers wanted to mimic what happens when most people diet, so they did not offer behavior modification or extensive clinical supervision to study subjects. Participants met with a registered dietitian at the start of the study and again at three, six and 12 months. They were randomly selected for either the conventional low-fat, high-carbohydrate diet or the high-fat, low-carbohydrate Atkins’ diet. The conventional dieters were given instructional materials for a 1,200-1,500 calories per day (women) or 1,500-1,800 calories per day (men) diet that consisted of 60 percent carbohydrate, 25 percent fat and 15 percent protein, based on the Food Guide Pyramid. The other group was instructed to read and follow the diet prescribed in Dr. Atkins’ New Diet Revolution.

At three months, those on the Atkins’ diet lost an average of 17.6 pounds while the conventional dieters lost about 8.3 pounds. After six months, those on the Atkins’ diet had lost an average of 21.2 pounds while those on the conventional diet lost an average of 11.5 pounds.

At 12 months, the Atkins’ diet group was down an average of 15.9 pounds versus 9.7 pounds for those on the conventional diet. The difference is not considered statistically significant, partly because almost half of the participants dropped out of the study before the one-year mark.

HDL cholesterol levels were up 11 percent at one year in the Atkins’ diet group, compared to an increase of only 1.6 percent on the conventional diet. Serum triglycerides declined an average of 17 percent after one year on the Atkins’ diet versus no significant change among conventional dieters. Part of that improvement may result from greater weight loss, but the changes in HDL cholesterol and triglycerides were greater than expected from moderate weight loss alone.

Klein led the study at Washington University. Gary Foster, Ph.D. associate professor of psychiatry and clinical director of the Weight and Eating Disorders Program at the University of Pennsylvania, led the research team in Philadelphia. James Hill, Ph.D., professor of pediatrics and medicine and associate director of the Colorado Clinical Nutrition Research Unit, coordinated the research effort in Denver.

The same research team will recruit larger numbers of participants in a five-year, NIH-funded study of low- and high-carbohydrate diets. The researchers hope to more fully assess the benefits and risks of the diets on bone mass, kidney function, blood vessel health and exercise tolerance. They also will look at whether behavior intervention and modification might help people stick to these diets.

Because of the high amounts of fat that people consume on the Atkins’ diet, many have worried that over the long term, it might have serious side effects. The researchers found no differences in side effects during the 12 months of this study and even found benefits in blood lipid profiles, but they say they’ll look more closely at potential side effects in their next study.

“A calorie is still a calorie, whether the calorie comes from fat, carbohydrates or protein,” Klein says. “But it might be that certain types of calories are more filling than others and result in an overall decrease in total calorie intake.”

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Foster GD, Wyatt HR, Hill JO, McGuckin BG, Brill C, Mohammed BS, Szapary PO, Rader DJ, Edman JS, Klein, S. A Multicenter, Randomized, Controlled Trial of a Low-Carbohydrate Diet for Obesity. New England Journal of Medicine, vol. 348:21, pp. 2082-2090, May 22, 2003.

This research was supported by grants from the National Institutes of Health.