The majority of type 2 diabetic patients are overweight and any excess weight, or weight gain, adversely affects glycaemic control. Paradoxically, antidiabetic agents used to improve glycaemic control are frequently associated with weight gain, particularly insulin therapy. Such weight gain further deteriorates glycaemic control and increases insulin resistance. Understanding body weight regulation in type 2 diabetic patients is therefore necessary to better adapt for the effect of such medication on weight. Expressed in terms of energy, weight gain results from positive energy balance. Positive energy balance in type 2 diabetes is most usually attributed to decreased energy expenditure and the cessation of glycosuric energy loss following the initiation of hypoglycaemic treatment. It appears from current literature however that these two factors, even in combination, cannot completely explain observed weight gain. Indeed, the precise contribution of energy intake and appetite, a key determinant of energy intake, to this positive energy balance remains a black box. In this review the potential contribution of a change in feeding regimen to weight gain associated with insulin treatment is assessed, with particular attention being paid to insulins effect within the brain.