The current project is a randomized controlled multi-centre clinical trial, in a cohort of children aged 3 to 6 years at baseline and being at obesity risk. The main objective consists on assessing the efficacy of an intervention during early childhood, considering a healthy lifestyle based on the promotion of a Mediterranean dietary pattern and regular physical activity, compared with a control group, on decreasing obesity incidence 5 and 10 years after the beginning of the intervention. It is envisaged to include 738 children, aged 3 to 6 years, having at baseline a body mass index (BMI) \< than the equivalent to 30 kg/m2 in adults, and at least one parent having a BMI \> 25 kg/m2. The clinical trial will have two arms and will be performed in Primary Health centres in 3 cities: Córdoba, Santiago de Compostela and Zaragoza. The control group will receive usual care by healthcare professionals. The intervention group, will receive education on Mediterranean lifestyle (Mediterranean diet and physical activity promotion), combined with the provision of extra-virgin olive oil and fish, in order to be consumed at least 3 times per week. Physical activity sessions with a physical activity monitor will also be offered for free to the children (2 sessions of 60 minutes of moderate-vigorous physical activity, per week). The participants' degree of compliance with the intervention will be periodically monitored. The main outcome is the incidence of obesity and the secondary outcomes are changes in body composition, physical fitness and cardiovascular risk factors. We are targeting for a 10 year follow-up.