Low Fat vs. Low Carbohydrate Diet Strategies for Weight Reduction: A Meta- Analysis

Background: Overweight and obesity are a global crisis. Lifestyle interventions, including weight loss diets, are the first line treatment for this problem. In addition to energy restriction, some diets emphasize manipulation of macronutrient composition to promote weight loss. Such diets may be broadly classified into low fat and low carbohydrate diets. Objective: This meta-analysis was designed to compare low fat to low carbohydrate diets in terms of weight loss. Methods: Studies were included in the present meta-analysis if they were 1) well-designed randomized clinical trials comparing low fat to low carbohydrate diets; 2) included healthy overweight and obese adults; 3) had a followup of 12 weeks or longer; 4) measured weight loss as the a stated endpoint; 5) were published in 2010 or later. Results: Nine studies meeting all inclusion criteria were identified. Together, these studies included 1161 subjects, 592 of whom were exposed to low carbohydrate diets and 569 to low fat diets. Two of the included studies provided meals to participants. One study included two low-carbohydrate arms, one with high glycemic index and one with low glycemic index carbohydrates. A high degree of heterogeneity between studies was identified, I2=94.8, Q=154.8, p<0.001. In a random effects model, no significant advantage to either diet strategy could be identified – standardized difference in means 0.42, 95% CI: 0.13-0.98, p=0.14. None of the metabolic endpoints examined, including lipid profile (triglycerides, total, low or high density lipoprotein cholesterol), glucose of blood pressure differed by diet exposure. Conclusion: Both types of macronutrient-centered weight loss diets produced weight loss. Manipulation of macronutrient composition of weight loss diets does not appear to be associated with significantly different weight loss or metabolic outcomes.