Functional food products promote claims such as 'freedom from hunger' and 'feel fuller for longer'. A legislative framework has been established by the European Food Safety Authority to evaluate the validity of such claims: a claim must be substantiated by scientific evidence and should be clearly understood by consumers. Since consumed foods influence appetite by means of a system of physiological satiety signals, functional foods could in principle act by increasing the potency and/or duration of these signals. Importantly, what constitutes a useful action: a reduction in hunger, an increase in fullness, a change in food intake at a meal, an adjustment in daily energy balance or a reduction in body weight? Any claim should not go beyond the scientific evidence of an effect, and methods exist to scientifically evaluate claims. The wording of a claim is, therefore, critical. The difference between a proof of concept and a guarantee of success is an important point that needs to be conveyed to the consumer.