With an increasing number of studies describing the negative correlation of coffee consumption and the risk for type 2 diabetes mellitus, we were compelled to elucidate the nutrients which bring pharmacological effects on risk reduction for diabetes. In this review, the author's interest is focused on chlorogenic and caffeic acids derived from lightly roasted coffee beans, as well as nicotinic acid, volatile Maillard reaction products (vMRPs), and another structurally unknown compound contained in heavily roasted beans. Caffeine is a common compound in both lightly and heavily roasted beans and its anti-inflammatory effects on degenerative diseases such as diabetes mellitus has been reevaluated recently. The prophylactic effects of coffee on diabetes involve pleiotropy of plural components in accordance to the degree of the roasting. A new concept of nutritional blended coffee may be important to optimize the prophylactic effects of coffee on lowering the risk factors of diabetes and delaying the progress of diabetes complications as well.