The new field of epigenetics has shown that the choice of which of your genes are "expressed," or activated, is strongly affected by environmental influences.
This means that expression of your genes can change, and they are influenced by external factors.
One implication of this is that many health problems -- ranging from cancer to cardiovascular disease to neurological disorders -- can be caused at least in part by altered "histone modifications," which affect DNA.
According to Eurekalert:
“The good news ... is that ‘HDAC inhibitors’ can stop this degenerative process, and some of them have already been identified in common foods. Examples include sulforaphane in broccoli, indole-3-carbinol in cruciferous vegetables, and organosulfur compounds in vegetables like garlic and onions.”