Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss and Cardiovascular Risk Factors

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Abstract
In the past 4 decades, the prevalence of obesity among adults aged 20 to 74 years in the United States increased from 13% to 31%.1 In the United States, obesity results in an estimated 325 000 deaths annually2 and accounts for about 5.5% of total direct health care costs.3,4 At any given time, approximately 45% of women and 30% of men in the United States are attempting to lose weight.5 Numerous diets have been proposed to promote weight loss.6 Weight loss from certain diets may lead to prevention of type 2 diabetes and improved control of hypertension7 and may reduce cardiovascular morbidity and mortality. In a recent meta-analysis of randomized controlled trials, little evidence was found to support the use of diets other than low-fat diets for weight reduction.7 However, there is a lack of data from well-controlled trials about the most effective dietary approaches to achieve meaningful and long-term weight loss in overweight individuals. Although fat- and energy-restricted diets are generally recommended for these individuals,8,9 low-carbohydrate, high-protein diets are one of the most popular alternative weight loss approaches.10 Low-carbohydrate diets derive a large proportion of energy intake from protein and fat, and there is concern for the potentially detrimental impact of these diets on blood lipid levels and on cardiovascular risk.11 Results from individual clinical trials and uncontrolled studies suggest that there is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets.12