How Genetics Influence How Coffee Affects You 

One of the reasons there have been so many conflicting studies on coffee is because the large majority of these studies are epidemiological. This means they don't look at cause and effect but rather associations. When it comes to coffee, the genetic predisposition of the individuals in the study group is what determines the outcome.  

Eating isn't only for fuel. That is to say, not all of the food you eat gets metabolized for energy. Some dietary chemicals peel off during the assimilation process and become ligands, molecules that bind to proteins responsible for the activation of certain genes. This played, and continues to play, a very important role in genetic information influenced by your environment.