The first 1000 days of life (from conception to two years of age) are highlighted in this thesis as a crucial period for the prevention of overweight.

This PhD thesis showed that a healthy respectively unhealthy lifestyle of mothers during pregnancy could change the DNA methylation of their children (measured in umbilical cord blood). An important lifestyle factor during pregnancy that changed DNA methylation was maternal smoking; studies in this thesis showed that hundreds of genes of newborns could be influenced by smoking of the mother. New-born babies of smoking mothers weighed on average 200 grams less than the babies of non-smoking mothers. Nearly 20 percent of this lower birth weight could be accounted for by the change in DNA methylation in one gene that we studied. Our expectation is that, through DNA methylation, a child can be programmed during pregnancy as susceptible or resilient to the unhealthy “obesogenic” environment later in life.

In this thesis we showed that growth in the first years of life played an important role in the development of overweight. Growth in the first six months was highly dependent on birth weight and breastfeeding. Additionally, we showed that dietary habits (fruit, vegetables, sweetened beverages and snacks) in toddlers were already related to deviation from the normal growth curve. Skipping breakfast was not yet a problem in Dutch five year old children. This behaviour will probably start to play a role at a later age.