Scientific and medical studies report that the environment, and particularly physical activity and the diet, changes the metabolic programming. A systematic review of size and growth during infancy supports conclusions with regard to preventing later obesity. Moreover, the correlation has been established between birth weight, arterial blood pressure, plasmatic lipid level, and cardiovascular mortality. The European Nutrition Committee has written new recommendations with lower protein levels. A lot of data support the application of blocking sensibilisation through intervention in pregnancy and lactation. Primary prevention is possible with breastfeeding for the first 4-6 months of life, particularly for high-risk allergic families. This is a priority for the national health program in France for controlling the increasing obesity.