Energy Intake

Food intake is regulated by various receptor systems. Direct stimulation of Serotonin 1A subtype (5-HT1a) and noradrenergic a 2-receptors will increase food intake, whereas Serotonin 2C subtype (5-HT2c) and noradrenergic a 1-or ( 2-receptor activation decreases food intake. Stimulation of histamine receptor subtypes 1 and 3, and dopamine receptors 1 and 2 result in lower food consumption. Recently, the cannabin-oid receptor (CB1), which is a G-protein-coupled receptor in the endocannabinoid system, has been identified and associated with food intake and regulation of energy homeostasis.16-18 Inhibition of CB1 is shown to decrease the craving for food, res-

ulting in weight loss when coupled with dietary and lifestyle modifications. In addition to receptor-modulated food consumption, higher levels of the protein leptin are associated with decreased food intake.20 In contrast, elevated levels of neuropeptide Y increase food intake.20

It is debatable whether obesity is related to total calorie intake or composition of macronutrients. Of the three macronutrients (i.e., carbohydrate, protein, and fat), fat has received the most attention, given its desirable texture and its ability to augment the flavor of other foods. Food high in fat promotes weight gain, in comparison with the other macronutrients, because fat is more energy-dense. When compared with carbohydrate and protein, more than twice as many calories per gram are contained in fat. In addition, fat is stored more easily by the body compared with protein and car-21

bohydrate.

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