Low-carb, not low-fat, diet linked with increased weight loss

1. From a randomized, parallel trial, a low-carbohydrate diet was associated with greater weight loss and cardiovascular risk factor reduction when compared to a low-fat diet.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Obesity has been established as an important, and increasingly prevalent, risk factor for cardiovascular disease CVD). Prior research has suggested that dietary strategies for weight loss have variable efficacy. The authors of this study investigated whether a low-carbohydrate or low-fat diet would be more effective in promoting weight loss and reducing other CVD risk factors. Individuals with a body mass index (BMI) greater than 30kg/m² were randomly assigned to either low-fat or low-carbohydrate diets. Patients with history of CVD were excluded form the study. After 12 months, those assigned to the low-carbohydrate group experienced significantly more weight loss than those in the low fat group. Furthermore, the low-carbohydrate diet was associated with significantly increased levels of high-density lipoprotein (HDL), decreased levels of triglycerides, and decreased fat mass compared to the low-fat diet. The greatest weaknesses of this study were the lack of blinding in both the participants and dieticians. As well, the study failed to include important long-term clinical endpoints such as mortality, stroke and cardiovascular events.

Click to read the study, published today in the Annals of Internal Medicine

Relevant Reading: Low-Carbohydrate-Diet Score and the Risk of Coronary Heart Disease in Women

In-Depth [randomized controlled trial]: This study included 148 participants with BMIs between 30-45. The participants were randomized to either low-carbohydrate diet (mean daily calories at 12 months = 1448) or low-fat diet (mean daily calories at 12 months = 1527). The low-carbohydrate diet led to significantly more weight loss of -5.3kg, compared to -1.8kg in the low-fat group. The lean mass also increased more in the low-carb group (1.3 vs. -0.4%), and the fat mass decreased more in the low-carb group (-1.2 vs. 0.3%). Unfortunately, neither diet showed a significant decrease in LDL, total cholesterol, blood pressure, plasma glucose, or insulin level. Importantly, C-reactive protein levels were decreased much more in the low-carb group (-6.7 vs. 8.6 nmol/L, p=0.024), and the 10-year Framingham risk score was similarly decreased (-1.0 vs. 0.4%, p<0.001).

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