Conditioned satiety in humans revisited

It is well established that the hedonic quality of the flavour of food (i.e. palatability) is an important determinant of short-term food intake. Detailed analysis of changes in appetite within meals suggested that palatability effects are generated through orosensory reward mechanisms which translate the hedonic evaluation of orosensory stimulation by food into enhanced motivation to eat, indicated by increased hunger in the early stages of meals with palatable foods. However, the hedonic quality of food is in a large part a learned response. Two distinct but interacting types of association may partly underlie the acquisition of palatability. The first, flavour¿flavour learning, is based on associations between new flavour elements and existing liked or disliked components such as sweet tastes, while the second, flavour-consequence learning, is based on associations between flavours and post-ingestive effects of nutrients. While many studies have demonstrated that both these associations can increase liking, only recently have we been able to assess whether these acquired likes also stimulate intake. Our recent finding that flavour¿nutrient associations can stimulate intake suggest that energy-dense foods may promote active as well as passive over-consumption, while new data also suggest enhanced appetite through flavour-flavour associations. The implications of these observations for understanding overeating in the context of the current obesity crisis is explored