Are low-carb diets better than low-fat diets for weight loss? Original paper

Many people use low-carbohydrate diets for weight loss because these diets have a tendency to reduce insulin levels and appetite. However, evidence comparing the efficacies of low-carbohydrate and low-fat diets suggests that differences between the two come down to personal preference.

This meta-analysis of randomized controlled trials assessed the relative effectiveness of low-fat/high-carbohydrate (LFHC) and low-carbohydrate/high-fat (LCHF) diets on weight loss and cardiovascular risk factors. Eleven studies assessing 739 participants were included. The studies were at least 4 weeks long and evaluated patients with overweight or obesity but without cardiovascular disease (i.e., coronary heart disease or heart failure) or cardiovascular risk factors (i.e., hypertension, high cholesterol, or dyslipidemia). LFHC diets provided ≤30% of calories from fat, ≤10% from saturated fat, and >45% from carbohydrates. LCHF diets provided <26% of calories from carbohydrates or <130 grams of carbohydrates per day.

The primary outcome was the difference in weight loss between the diet groups. The secondary outcomes were changes in lean mass, fat mass, systolic blood pressure, total cholesterol, triglycerides, LDL-C, HDL-C, and blood glucose.

Compared to LFHC diets, LCHF diets resulted in a greater weight loss (−1.01 kg) and a greater increase in HDL-C (+7.7 mg/dL). However, LCHF diets resulted in a smaller decrease in total cholesterol and LDL-C (−24.4 and −22.8 mg/dL, respectively). There were no differences between groups in lean mass, fat mass, blood pressure, triglycerides, or blood glucose.

It is notable that although weight loss was greater in the LCHF group, fat loss didn't differ between groups. The difference in weight loss might be primarily due to the decreases in stored glycogen and associated body water that are common in low-carbohydrate diets. Additionally, only one of the studies equated protein intake between groups; in the other studies, the LCHF groups consumed more protein than the LFHC groups.