BOX 3-3

Food Intake Regulatory Systems

In 1994, it was discovered that a peptide hormone—leptin—is manufactured and secreted by fat cells, travels through the circulatory system, crosses the blood-brain barrier, and acts on the brain’s hypothalamus to influence appetite (Zhang et al., 1994). This finding has led to the concept of a “fat-brain axis” (Elmquist and Flier, 2004), a pathway by which events in the periphery of the body are communicated to the brain. As a result, the brain may “monitor” the body’s energy or adipose stores and, when indicated, start a chain of events that either initiates or terminates feeding.

There is now evidence that leptin affects both neuronal activity (Pinto et al., 2004) and synaptic plasticity (Bouret et al., 2004) in the arcuate nucleus of the hypothalamus, which is home to two distinct populations of neurons with opposing actions—one group that stimulates food intake and another that suppresses it (Elmquist and Flier, 2004). Furthermore, Bouret and colleagues (2004) suggest that leptin plays a neurotrophic role during the development of the hypothalamus that is restricted to a “neonatal critical period”—that is, the plasticity present early in life is apparently lost by adulthood. Although it is widely appreciated that good nutrition and a healthful lifestyle during the pregnancy period are important for producing healthy babies, these findings raise the possibility that the baby’s food-intake and body fat regulatory systems may be permanently shaped during this period.

Future research undoubtedly will be directed to determining whether this communication system is indeed fundamental to the mechanisms of food-intake and body fat regulation in humans, and whether its timing is so narrowly focused.

Psychosocial and Behavioral Considerations

Dietary Intake

Everyone needs to eat food and consume beverages for daily sustenance. But beyond the physical necessities are the complex social, cultural, and emotional nuances that involve food and permeate many facets of daily life. Children and adults alike consume food and beverages in part because they are hungry but also because eating and drinking are pleasurable and are an integral part of family life, celebrations, recreational events, and other social occasions. Food is also important in the psychosocial well-being, emotional expression, and coping responses of many people. It is, therefore, unrealistic to base recommended eating patterns solely on the chemical composition of foods without taking cultural, social, economic, and emotional drivers of food consumption into account. Furthermore, while few would dispute the negative aspects of individual substances such as tobacco, alcohol, or illegal drugs, there have been strong debates over



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