BACKGROUND: Many methods are available to determine energy requirements, however, all have limitations, particularly when used for the obese. OBJECTIVES: The aim of this survey was to investigate current practice in the estimation of energy requirements in an underweight and obese hospitalised patient in a large cohort of UK dietitians. SUBJECT/METHODS: A cross-sectional anonymous online survey of UK registered dietitians was performed. RESULTS: A total of 672 responses were received. Underweight patient: prediction equations with adjustment for metabolic stress and physical activity were most commonly used (90%). The median estimated energy requirement was 2079 kcals/day. The estimated energy requirement using calorie per kilogram method was significantly lower compared with equations (P<0.001). The median target volume of feed prescribed was 2000 mls/day. A significant reduction in feed prescribed compared with estimated energy requirements was found (P<0.001). Obese patient: prediction equations to estimate the basal metabolic rate alone were most commonly used (51%). Nutrition support dietitians used a lower stress factor compared with non-nutrition support dietitians (P=0.016). Method used to estimate the energy requirements was associated with years in clinical practice and place of work (P<0.001, 0.001). Calorie per kilogram used in the obese case study (median: 25 kcal/kg) was significantly lower than calorie per kilogram used in the underweight case study (median: 30 kcal/kg; P=0.014). CONCLUSIONS: A significant variation in the methods used by dietitians to estimate the energy requirements was found, particularly in the obese patient group. In an age of rapidly increasing rates of obesity a professional consensus of treatment of this patient group is needed.