This little video beautifully explains the concept of nutritional epigenetics. Working with international researchers, we published in 2013 a review on this topic:
Jalili M, Pati S, Rath B, Bjørklund G, Singh RB. Effect of Diet and Nutrients on Molecular Mechanism of Gene Expression Mediated by Nuclear Receptor and Epigenetic Modulation. Open Nutra J 2013;6:27-34.
Dietary and lifestyle choices can have a negative or a positive effect.