Comparison of Weight Loss at 2 Years on a Low-Carbohydrate Versus Low-Fat Diet. Ann Intern Med. 2010;153:I-35. doi: 10.7326/0003-4819-153-3-201008030-00002
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Published: Ann Intern Med. 2010;153(3):I-35.
Low-carbohydrate diets are popular among persons who want to lose weight. Although previous studies suggest that more early weight loss occurs with low-carbohydrate diets than low-fat diets, the results after 1 year are mixed. In addition, any weight loss after 1 year tended to be small. However, studies comparing these 2 types of diets have not included comprehensive behavioral support programs to help patients change other aspects of their lifestyle. It is possible that persons could lose more weight if diet is combined with such a program.
The researchers wanted to compare weight loss after 2 years on a low-carbohydrate diet versus a low-fat diet when both are combined with a program to help patients change their lifestyle.
The study included 307 persons with a body mass index (BMI) of 30 to 40 kg/m2. Body mass index is a measure of the appropriateness of a person's weight. It is calculated by dividing weight in kilograms by the square of height in meters. A BMI calculator is available from the National Heart, Lung, and Blood Institute (www.nhlbisupport.com/bmi). Normal BMI is 18.5 kg/m2 to 24.9 kg/m2. Persons with BMIs of 25 kg/m2 to 29.9 kg/m2 are overweight, and persons with BMIs of 30 kg/m2 or more are obese.
The researchers assigned patients to either a low-carbohydrate or a low-fat diet. They instructed the low-carbohydrate group to eat no more than 20 grams of carbohydrate per day for 3 months and then increase by 5 grams per day each week until they achieved their desired weight. The low-fat diet group received instructions to decrease calorie intake to 1200 to 1800 kcal per day with no more than 30% of calories from fat. All patients also participated in an education program on changing physical activity and other lifestyle factors. This program met weekly for 20 weeks, then every other week for 20 weeks, and then monthly for the rest of the 2-year study. The researchers collected information about weight at the start of the diet and after 3, 6, 12, and 24 months. They also collected information on cholesterol levels, blood pressure, bone density, and side effects.
After 2 years, patients lost an average of 7 kg or 7% of body weight, and no differences between the 2 groups were found. The low-carbohydrate group had some more favorable changes in risks factors for heart disease at year 2 compared with the low-fat diet group.
The study did not include persons with cholesterol problems or diabetes, so the results might not apply to patients with these conditions. Many withdrew from the study by 2 years.
After 2 years, patients can have similar amounts of successful weight loss with either a low-fat or low-carbohydrate diet combined with a behavioral program to help patients change their lifestyle. A low-carbohydrate diet may modestly improve some, but not all, risk factors for heart disease. It is unknown whether these improvements will influence the future development of heart disease.
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