Obesity is a well-recognised risk factor for the development of type 2 diabetes. This relationship will be explored mainly from an adipocyte biology perspective, to explain the pathophysiological processes linking obesity with the development of diabetes. Obesity relates to a state of energy excess where inappropriate storage of this energy leads to insulin resistance and pancreatic dysfunction. Treatment of diabetes, utilising very low-calorie diets or bariatric surgery, demonstrate the importance of excess energy in the pathophysiology of diabetes and how remission can be induced by reaching a negative energy balance.