According to WHO reports diet factors influence occurrence of more than 2/3 of diseases. Most of these factors belong to the categories of nutrigenetics a nutrigenomics. Nutrigenetics concerns individual differences in the reaction to food based on the genetic factors. Nutrigenomics analyses direct influences of nutrients on gene expression. Both terms are explained in our review article. Importance of nutritional factors is explained on differences of epidemiology of the same disease in different countries and on the examples of interaction of nutrition and genes for hypertension, atherosclerosis and cancer. In the future both, nutrigenetics a nutrigenomics, will induce many changes in preventive and also in clinical medicine.