Epigenetics studies hereditary changes in gene and phenotypic expression, which do not leave any trace on the DNA molecule, as well as transgenerational effects of environmental factors. For a clear perception of the definition of epigenetics, this graduation thesis describes some basic notions of genetics, regulatory mechanisms controlling gene expression, and the main molecular mechanisms of epigenetics: DNA methylation, histone modifications, and RNA interference. Each of the mechanisms listed above can be compared to a switch, which 'turns off or on' a specific gene, thus deciding upon their expression. This is the reason we can refer to the epigenome as 'an additional layer' of genetic information, (de)activated by certain mechanisms if there is an external factor, called epigenator, influencing them. Food is the basic fuel for human organism from which we extract usefull, as well as some harmfull substances too. Two experiments conducted on mice have been described. The mice were fed by specific food, which than changed certain phenotypic characteristics of their offsprings. This made us realize that human life is determined not just by inherited genes, but also by a number of external factors, which we can influence.