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

Abstract

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.