Children obesity and changing habits (COACH)The prevalence of obesity in children and adolescents has increased rapidly in developed countries across the globe and has become a concern for its potential negative consequence on health. The prevalence rate of obesity among children and adolescents in developed countries is over 20% and in the UK it is even higher than 25%. The COACH project aims at assessing the determinants of obesity and overweight in children by looking at their eating habits and active lifestyle and evaluating (1) how changes in health habits can help reducing child obesity; (2) how these habits can be modified trough three mechanisms which are: I. the transmission of healthy habits from parents to children, II. the effect of environmental factors, III. the effect of habits of the child’s peers. Parents can have a big role in transmitting healthy habits and obesity to their children. Children whose parents have bad eating habits and sedentary lifestyles may end up acquiring the same type of habits. Similarly children habits can be affected by the lifestyle and behaviour of other children they share their time with, e.g. siblings and school mates. Finally, a big influence on children’s health habits may come from the environment where they live. Environments with a lack of parks and green spaces, cycle paths and road safety can impede an active lifestyle. Similarly bad eating habits can be promoted by environments with an abundance of fast-food restaurants and a scarcity of shops providing quality fruits and vegetables.Assessing the relative importance of different mechanisms affecting child’s habits and identifying which among different health habits is most malleable and has the largest effect on obesity will inform policy makers on how to design more cost effective strategies to tackle obesity.