title: Sympathetic nervous system response to intake.
abstract: Meals increase the activity of the sympathetic nervous system (SNS) above the activity level observed in the postabsorptive state. Pharmacologic blockade of the thermogenic effect of norepinephrine, the primary neurotransmitter of the SNS, suggests that this response accounts for approximately 20% of the thermic response to food. Energy expenditure increases after several days of sustained overeating. There is no convincing evidence that this response is mediated by increased SNS activity in humans, as it is in some animals. Energy expenditure decreases within a few days of energy deprivation. When sodium balance is maintained, energy deprivation also reduces SNS activity. The reduced SNS activity may contribute to the decreased energy expenditure, but cannot explain it completely. The contribution of the SNS to total energy expenditure is small in normal subjects consuming a weight-maintenance diet, probably < 5%. A few studies have suggested that SNS activity is reduced in obese humans, suggesting that low energy expenditure associated with reduced SNS activity may contribute to obesity. However, a critical evaluation of the available evidence indicates that this hypothesis is untenable.
mesh_terms: D000818:Animals; D004032:Diet; D004435:Eating; D002149:Energy Intake; D004734:Energy Metabolism; D006801:Humans; D009638:Norepinephrine / Q000502:physiology; D009765:Obesity / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D009638:Norepinephrine