Obesity prevalence rates have risen substantially in several countries during the last decades. The factors behind this trend are not fully understood. Notwithstanding the influence of genetic factors, however, a general result is that obesity is caused by a caloric intake that exceeds the caloric expenditure from physical and psychological exercise. The development of obesity is thus, to a large degree, a result of the individual’s everyday decisions regarding food consumption and exercise. Accordingly, assuming people act rationally, there would be no cause for concern but for the fact that obesity increases morbidity risks. The associated increase in the costs of illness is to a large part born by society, and not by the individual. The question is then whether preventative measures – and if so, which preventive measures – against obesity would be efficient? The study analyses the evidence base for different types of such measures in the clinical and economic literature, and offers some plausible hypotheses of the rather discouraging results.