Weight Loss and Results of Low-Carbohydrate Diets. Ann Intern Med. 2004;140:I-27. doi: 10.7326/0003-4819-140-10-200405180-00002
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Published: Ann Intern Med. 2004;140(10):I-27.
Low-carbohydrate diets are popular among people who want to lose weight. Many people believe that more weight can be lost with low-carbohydrate diets than with diets that restrict calories and fat. A concern is that low-carbohydrate diets might have an unfavorable effect on metabolic factors such as cholesterol level and other types of fats in the blood that are linked to heart disease. However, low-carbohydrate diets may be beneficial for other metabolic factors, such as blood sugar, that are linked to diabetes. In 2003, these researchers reported that adults assigned to a low-carbohydrate diet lost more weight after 6 months than did adults on a low-fat diet. The low-carbohydrate diet group also had greater improvements in metabolic measures than did the low-fat diet group. Other studies suggest that people on low-carbohydrate diets regain weight by 1 year.
To determine the effect of a low-carbohydrate diet on weight and metabolic factors after 1 year.
132 severely overweight adults. To participate in the study, people had to have a body mass index (BMI) of at least 35 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 (http://www.nhlbisupport.com/bmi). Normal BMI is 18.5 kg/m2 to 24.9 kg/m2. People with BMIs of 25 kg/m2 to 29.9 kg/m2 are overweight, and people with BMIs of 30 kg/m2 or more are obese.
The researchers assigned patients to either a low-carbohydrate diet or a conventional low-fat weight loss diet. They instructed the low-carbohydrate group to eat no more than 30 grams of carbohydrate per day. The conventional diet group received instructions to decrease calorie intake by 500 calories per day and have less than 30% of total calories from fat. The researchers collected information about weight at the start of the diet, after 6 months, and after 1 year. They collected blood specimens to test the levels of metabolic factors.
After 1 year, patients in the low-carbohydrate group had more favorable levels of 2 types of blood fats (triglycerides and high-density lipoprotein cholesterol) than did patients on the conventional diet. However, weight loss and the other metabolic factors were similar in the 2 groups.
Because the study included only severely overweight people, results might not apply to people with less severe weight problems. In addition, many people dropped out of the study by 1 year.
After 1 year, the low-carbohydrate diet provided no weight loss advantage over the conventional, low-fat diet. However, a low-carbohydrate diet may modestly improve some, but not all, metabolic factors. It is unknown whether these improvements will influence the future development of diabetes and cardiovascular disease.
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