Behavioural strategies in the regulation of food choice.

The maintenance of nutrient and energy balance in the body depends on both metabolic and behavioural mechanisms, and is integrated by the brain. The regulatory system was developed by natural selection and not by mechanical engineers. Thus, rather than having unitary mechanisms regulating intake of each nutrient, evolution has incorporated and used a multitude of behavioural traits and metabolic adaptations. The criterion for inclusion was that each one conferred a persisting advantage in the prevailing environment. Behavioural strategies in food choice include: innate preference for sweetness and an aversion towards bitter tastes, a hesitancy towards unknown foods, preference for variety among familiar foods, and a special ability (long delay learning) to acquire information about both positive and negative metabolic consequences of eating different foods. In man, these more basic mechanisms interact with and are complemented by cognitive, social and cultural influences on food choice. In a very few cases, such as regulation of energy, sodium and (perhaps) protein intakes, feeding behaviour is also guided by signals from specific internal receptors. However, for most nutrients, appetites seem to be non-specific and learned. Using studies on the regulation of protein intake from our own and other laboratories as examples, this review illustrates how innate preferences, learning, social interactions, metabolic adaptation and diet-induced changes in brain neurotransmitter metabolism can all play a role in subjective decisions about what to eat.