This guideline covers behaviours such as diet and physical activity to help children (after weaning), young people and adults maintain a healthy weight or help prevent excess weight gain. The aim is to prevent a range of diseases and conditions including cardiovascular disease and type 2 diabetes and improve mental wellbeing. The recommendations support those made in other NICE guidelines about how to prevent people becoming overweight or obese. This includes interventions and activities in which weight is not the primary outcome, such as those aimed at preventing cardiovascular disease or type 2 diabetes, improving mental wellbeing or increasing active travel.