About 12% of the adult Dutch population is obese (Quetelet Index > or = 30 kg/m2). The prevalence has roughly doubled over the past 20 years. Obesity is strongly associated with a number of chronic diseases, such as type 2 diabetes mellitus, increased healthcare costs and a loss of productivity. Obesity is always the result of a mismatch between energy intake and energy expenditure. Foods with a high percentage of energy derived from fat are associated with weight gain, particularly when the rest of the energy is obtained from products containing little dietary fibre. Foods with a high content of refined added sugars or starch might be unfavourable with respect to the energy balance and the risk for type 2 diabetes mellitus and cardiovascular diseases. Slimming diets should aim for a gradual and sustained weight loss of about 10% of the initial weight over a period of six months, followed by weight maintenance over the next two years. Physical activity is an essential component of a weight loss strategy. Moderate sustained weight loss is associated with a strong reduction in the risk of type 2 diabetes mellitus in people with impaired glucose tolerance.