Not only does what you eat have a direct effect on your biology, but there's also the indirect effect on your gut bacteria which in turn has a direct effect on your biology.
Of particular concern among scientists and the public is the effect that gut flora may have on mental health, as a mounting body of research suggests that gut bacteria can have a significant impact on the way we think, feel and behave, and also on the development of neurological conditions. Last year, a major neuroscience symposium called the investigation of gut microbes a “paradigm shift” in brain science.
LINK: http://www.huffingtonpost.com/2015/02/12/gut-bacteria-health_n_6480580.html