There is a pandemic of diabetes in the US and around the world. There are two types of diabetes, type 1 and type 2, with type 2 diabetes being most common and strongly associated with obesity. Diabetes and obesity run in families and are highly hereditary, but the epidemic is also due to the impact of the modern environment, including fattening diets, not enough exercise, and exposure to light around the clock especially for people doing shift work. These environmental challenges overwhelm normal physiology, in large part by altering the expression of genes in tissues important for metabolism. The factors other than the sequence of the genome that determine how genes are expressed are collectively referred to as the epigenome. The Lazar lab studies how and what goes wrong with the epigenome in obesity and diabetes.