Thoughts and beliefs has not yet been proved playing role in epigenetics but certainly what we eat shows its effect on our epigenetics.one of the study says what grand mother had eaten it will affect the epigenetics of individual.

See this http://www.norcalcs.org/2013/06/genetics-epigenetics-and-mind-body.html

Bruce Lipton offers some interesting insights into this topic. You may find his website informative http://www.brucelipton.com

Apart from his attempt at exploring the direct effect of the mind on gene control, thoughts and beliefs may have an indirect effect on gene activity by influencing our lifestyle choices, with epigenetic implications.

This is a subject where we should be very cautious in taking conclusions that data does not suport.

As far as we know, epigenetics are important to phenotypes, and the environment is important to epigenetics. The most interesting epigenetic system are the responsive ones, so depending on the environment and stress condition on the organisms on it, responsiviness can play a central role on plasticity and adaptation, which potentially will influence health, heredity, ecology and evolution.

As Mustapha said, our behavior can influence environment and environment can influence ou phenotypes, so indirectely, we are affecting our own phenotype in some way. As consequences to some patterns of strees, some epigenetic changes can arise, adaptatively or accidental, and for "good or bad" outcomes.

But when we say that though and beliefs are affecting our gene's function, seems that we are suggesting some form of control, a very onerous claim, for which we have no evidence to date. Ideas like those o Lipton are far from having evidence.

Research shows certain states of mind influence physical health!!!

http://www.nature.com/news/immunology-the-pursuit-of-happiness-1.14225?WT.mc_id=FBK_NPG_1311_NatureNews.