Objective: To investigate the relative efficacy of four popular weight-loss programmes on plasma lipids and lipoproteins as measures of CVD risk. Design: A multi-centred, randomised, controlled trial Of four diets - Dr Atkins' New Diet Revolution, The Slim-Fast Plan, Weight Watchers Pure Points Programme and Rosemary Conley's `Eat Yourself Slim' Diet and Fitness Plan - against a control diet, in Parallel for 6 months. Setting and subjects: The trial was conducted at five universities across the UK (Surrey, Nottingham, Ulster (Coleraine), Bristol and Edinburgh (Queen Margaret University College)) and involved the Participation of 300 overweight and obese males and females aged 21-60 years in a community setting. Results: Significant weight loss was achieved by all dieting groups (5-9 kg at 6 months) but no significant difference was observed between diets at 6 months. The Weight Watchers and Rosemary Conley (low-fat) diets were followed by significant reductions ill Plasma LDL cholesterol (both -12.2% after 6 months, P < 0.01), whereas the Atkins (low-carbohydrate)and Weight Watchers diets were followed by marked reductions in plasma TAG (-38.2% and -22.6% at 6 months respectively, P < 0.01). These latter two diets were associated with an increase in LDL Particle size, a change that has been linked to reduced CVD risk. Conclusions: Overall, these results demonstrate the favourable effects of weight loss on lipid-mediated CVD risk factors that can be achieved through commercially available weight-loss programmes. No detrimental effects on lipid-based CVD risk factors were observed in participants consuming a low-carbohydrate diet.