Obesity is a major public health problem in the US population. Low carbohydrate diets are popular as a means of weight loss; however, there is concern for adverse effects on cardiovascular (CV) risk factors. We conducted a meta-analysis of randomized controlled trials comparing the effect of low carbohydrate diets (≤45% of energy from carbohydrates) versus low fat diets (≤30% of energy from fat) on CV risk factors, including systolic and diastolic blood pressure, total cholesterol, high-density-lipoprotein (HDL) cholesterol, low-density-lipoprotein (LDL) cholesterol, triglycerides, body mass index, waist circumference, fasting blood glucose and serum insulin. We searched MEDLINE, EMBASE, Web of Science and the Cochrane Database of Systematic Reviews, and manually examined references in selected articles and relevant literature reviews. Information on participant characteristics, trial design and duration, dietary composition, and CV risk factors were extracted using a standardized protocol. Random effects models were used to pool mean differences between CV risk factors on the two diets. From 785 potentially relevant publications, 23 randomized controlled trials compared low carbohydrate diets with low fat diets with intervention duration ≥ 6 months and reported CV risk factors as primary outcomes. These studies included data from 2,961 participants in total. The average percent of energy from carbohydrate intake was 20.7% on low carbohydrate diets and the average percent of energy from fats was 25.9% on low fat diets. Compared to participants on low fat diets, those on low carbohydrate diets showed favorable changes in HDL cholesterol, triglycerides and body mass index, with pooled net changes (95% CI) of 3.2 mg/dL (1.9, 4.5), -13.0 mg/dL (-17.3, -7.8) and -0.4 kg/m2 (-0.7, -0.1), respectively. After removing studies without intention-to-treat analysis, the change in body mass index was no longer significant (N=16). Changes in total and LDL cholesterol favored low fat diets, but after accounting for publication bias, results were no longer significant for total, LDL and HDL cholesterol. In conclusion, our findings show that low carbohydrate diets were at least as effective as low fat diets for weight loss, and did not have significant adverse effects on other CV risk factors. In fact, low carbohydrate diets had a significant and favorable impact on triglycerides. These findings suggest that low carbohydrate diets can be recommended to obese persons with CV risk factors for the purpose of weight loss.
Adherence to low‐carbohydrate and low‐fat diets in relation to weight loss and cardiovascular risk factors