In the UK, over 50% of adults are overweight (body mass index [BMI] of 25-29.9 kg/m(2)) or obese (BMI 30 kg/m(2) or more); it is thought that over half of the UK population could be obese by 2050 because of the increasing availability of calorie-dense food and sedentary lifestyles.(1-3) Interventions to achieve weight loss include diets, increased physical activity, behavioural modification strategies, drugs (e.g. orlistat) and bariatric surgery.(4) Dietary interventions include low-calorie diets (LCDs; 1,000-1,200 kcal/day for women and 1,200-1,600 kcal/day for men), very low calorie diets (VLCDs; including Very Low Energy Diets [VLED]; below 800 kcal/day) and Low Energy Liquid formula diets (LELD; above 800 kcal/day).(4,5) However, drop-out rates from such interventions are often high. Here we consider the safety and effectiveness of VLCDs and practical issues about their use.