Dietary fat is strongly implicated in the development of insulin resistance and obesity, both major public health problems today. While the amount of dietary fat is relevant, the type of fat is important in fuel utilisation, storage and appetite regulatory mechanisms. Human calorimetry research confirms the importance of dietary fat in energy balance, but more work needs to be done to uncover the impact of type of dietary fat in weight control. Population and intervention research confirm the importance of fat in dietary interventions, bearing in mind the contribution of physical activity to energy balance. The food industry has an important role to play in strategic food innovation which addresses this expanding knowledge base.