Study: Low-Carb Diet More Effective Than Low-Fat Diet
DURHAM, N.C. -- People who followed a low-carbohydrate, high-protein diet lost more weight than people on a low-fat, low-cholesterol, low-calorie diet during a six-month comparison study at Duke University Medical Center. However, the researchers caution that people with medical conditions such as diabetes and high blood pressure should not start the diet without close medical supervision.
"This diet can be quite powerful," said lead researcher Will Yancy, M.D., an assistant professor of medicine at Duke University Medical Center and a research associate at the Veterans Affairs Medical Center in Durham, N.C. "We found that the low-carb diet was more effective for weight loss," Yancy added. "The weight loss surprised me, to be honest with you. We also found cholesterol levels seemed to improve more on a low-carb diet compared to a low-fat diet."
The study is the first randomized, controlled trial of an Atkins-style diet approach, which includes vitamin and nutritional supplements. Along with losing an average of 26 pounds, dieters assigned to the low-carbohydrate plan lost more body fat, and lowered their triglyceride levels and raised their HDL, or good cholesterol, more than the low-fat dieters. The low-fat dieters lost an average of 14 pounds. Though the low-fat diet group lowered their total cholesterol more than the low-carb dieters, the latter group nearly halved their triglycerides and their HDL jumped five points. The low-carbohydrate group reported more adverse physical effects, such as constipation and headaches, but fewer people dropped out of the low-carbohydrate diet than the low-fat diet.
The results appear in the May 18, 2004, issue of the Annals of Internal Medicine. The research was funded by an unrestricted grant from the Robert C. Atkins Foundation. The study authors have no financial interest in Atkins Nutritionals, Inc.
The study builds on earlier results by the Duke University Medical Center researchers showing a low-carbohydrate diet can lead to weight loss -- the first study of the low carbohydrate diet since 1980. Yancy and co-investigator Eric Westman, M.D., are currently testing whether a low-carbohydrate diet can help diabetics control their blood sugar levels.
Despite the considerable weight loss experienced by the low-carbohydrate dieters, Yancy does not recommend an Atkins-style plan for patients attempting to lose weight for the first time.
"Over six months the diet appears relatively safe, but we need to study the safety for longer durations," Yancy said. He also cautioned that the diet could present certain health risks, such as elevations in LDL cholesterol levels, bone loss, or kidney stones. This and other recent studies of the low-carbohydrate diet have not demonstrated that these health risks occur over short durations, but they might occur in people on the diet for long-term. It is especially important that people on diuretic or diabetes medications be monitored by a doctor because the low-carbohydrate diet affects hydration and blood sugar levels, Yancy said.
The 120 study participants were randomly assigned to either the low-carbohydrate, high-protein diet or the low-fat, low-cholesterol, low-calorie diet. All were between 18 and 65 years old and in generally good health, with a body mass index (BMI) between 30 and 60, indicating obesity, and a total cholesterol level of more than 200 mg/dL. None had tried dieting or weight loss pills in the previous six months.
The low-carbohydrate group was permitted daily unlimited amounts of animal foods (meat, fowl, fish and shellfish); unlimited eggs; 4 oz. of hard cheese; two cups of salad vegetables such as lettuce, spinach or celery; and one cup of low-carbohydrate vegetables such as broccoli, cauliflower or squash. They also received daily nutritional supplements recommended by Atkins -- a multivitamin, essential oils, a diet formulation and chromium picolinate. There were no restrictions on total calories, but carbohydrates were kept below 20 grams per day at the start of the diet.
The low-fat, low-cholesterol, low-calorie group followed a diet consisting of less than 30 percent of daily caloric intake from fat; less than 10 percent of calories from saturated fat; and less than 300 milligrams of cholesterol daily. They were also advised to cut back on calories. The recommended daily calorie level was 500 to 1,000 calories less than the participant's maintenance diet -- the calories needed to maintain current weight.
Study participants were encouraged to exercise 30 minutes at least three times per week, but no formal exercise program was provided. Both sets of dieters had group meetings at an outpatient research clinic regularly for six months.
Others members of the Duke research team were Maren Olsen, Ph.D.; John Guyton, M.D.; Ronna Bakst, R.D.; and Eric Westman, M.D., who was co-principal investigator for the study. The researchers maintained exclusive control of all data and analyses.