Exploring the highs and lows of very low carbohydrate high fat diets on weight loss and diabetes- and cardiovascular disease-related risk markers: A systematic review

Aim Very low carbohydrate high fat diets (VLCHF) are increasingly popular for weight loss and diabetes management, but the risk implications of long-term adherence to a high-fat-diet remain unclear, especially in high-risk populations. This review aimed to examine adherence, weight loss, diabetes- and cardiovascular disease (CVD)-related risk markers in adults consuming VLCHF diets. Methods Online databases were searched for randomised controlled trials >= 3 months duration that met a pre-defined macronutrient prescription: VLCHF <= 25%E carbohydrate, >35%E fat; low fat (LF) >= 45%E carbohydrate, <= 30%E fat; and reported energy, saturated fat (SFA), weight, blood glucose, cholesterol and blood pressure (BP). Studies were excluded if the macronutrient prescription was not targeted (n = 32); not met (n = 17) or not reported (n = 13). Results Eight studies included: 1217 commenced; 922 completed overweight and obese adults. Diets were isocaloric moderately energy-restricted, closely monitored with ongoing support from dietitians, physicians, and/or nurses. Four studies reported non-adherence beyond 3 months (n = 3) and 6 months (n = 1) despite interventions of 12, 15 and 24 months. VLCHF diets were high in fat and SFA (fat 49%-56%E; SFA 11%-21%E) compared to LF diets (fat 13%-29%E; SFA 5%-11%E). All groups achieved significant weight loss and improvements in BP and blood glucose. LDL-C reduction favoured LF, P < .05; increased HDL-C and reduced triglyceride levels favoured VLCHF, P < .05. Conclusions VLCHF and LF diets with moderate energy restriction demonstrate similar weight loss and improvements to BP to 3 months. However, adherence is likely poor without intensive support from health professionals. Dietary SFA should be monitored to ensure recommended intakes, but longer-term studies with high adherence are required to confirm the level of CVD-risk and potential harms.

Automated summary

The review found that very low carbohydrate high fat diets (VLCHF) and low fat diets showed similar weight loss and improvements in blood pressure with moderate energy restriction. However, adherence may be poor without intensive support from health professionals. Longer-term studies with high adherence are needed to confirm the level of cardiovascular disease risk and potential harms.