Learned influences on appetite and food intake: Evidence in human beings

Learning underlies the development and regulation of habitual eating, including our likes and dislikes, choosing foods most appropriate to our current motivational state, and controlling how much is eaten. In young children, mere exposure to the flavor of a food increases acceptance of that food. Similarly, exposure to flavors in amniotic fluid and breast milk might link maternal dietary choice with preference development in children. Children's preferences are strongly correlated with the energy density of foods because of the reinforcing effects of energy eaten when hungry, that is, flavor consequence learning. Carbohydrate, fat, and protein have all proved effective in reinforcing flavor preferences. Flavors associated with higher energy consumption are preferred when hungry, but conversely less liked when full than lower energy-paired flavors, and they suppress subsequent intake. Sensitivity to post-ingestive energy differences may weaken with age and externalization of eating control. Frequent eating of high fat energy-dense foods may impair neural inhibition of learned appetite, creating a vicious circle leading to obesity. Flavor-flavor learning occurs when a neutral flavor is eaten together with a flavor that already has strong positive or, more robustly, aversive properties. This could form a shortcut for transferring important information from one sensory property to another. The necessity for explicit awareness of flavor-consequence or flavor-flavor associations for learned control of eating is discussed. This is important because it has implications as to who should be held accountable for eating behavior, and so for public health strategies to control obesity and dietary-related disease.