Fetal nutrition may permanently affect physiological properties of the new individual and hence the risk of future disease. Epidemiological studies indicate that fetal nutrition may significantly influence the risk of diabetes, cardiovascular disease, and cancer. Controlled animal studies show that even properties traditionally considered as exclusively genetic, like fur colour, may be modified by altered maternal nutrition. The expression "fetal programming" has been introduced to describe permanent effects of environmental conditions in fetal life. An important mechanism of fetal programming seems to be epigenetic regulation. One example of epigenetic regulation is methylation of the DNA base cytosine in promoter regions of some genes. DNA methylation will lead to decreased gene expression. Over the last two decades, marked changes in dietary habits and other life style features have taken place among young Norwegian women. This is particularly reflected in the increasing prevalence of obesity. Maternal weight and metabolic status is closely associated with the growth and development of the fetus. Thus, diet and physical activity become particularly important aspects of the health of young women.