Influence of autonomic nervous system on nutrient-induced thermogenesis in humans.

Experiments that have investigated the possible influence of the sympathetic and parasympathetic nervous systems on the thermic response to intravenously and orally administered nutrients are discussed. Although two thermogenic components, obligatory and facultative thermogenesis, can be demonstrated with the hyperinsulinemic clamp technique, facultative thermogenesis is less obvious after oral administration and is probably the result of insulin-mediated sympathetic nervous stimulation. On the other hand, the parasympathetic system would appear to influence the thermic response to meal ingestion by modulating obligatory thermogenesis, i.e., the rate at which nutrients are digested, absorbed, and processed by the various tissues and organs of the body. In obese individuals, impaired activity of one or both branches of the autonomic nervous system has been observed in fasting postabsorptive conditions and, on some occasions, after meal ingestion. Autonomic nervous dysfunction may be a risk factor for obesity or associated with obesity, and its early detection could provide a means of identifying individuals at risk of becoming obese and/or diabetic so that appropriate treatment can be devised.