Reduced postprandial heat production with gavage as compared with meal feeding in human subjects.
The postprandial changes in resting metabolic rate (RMR) were measured in eight subjects after the ingestion of 735 kcal taken in the form of a meal or fed by stomach tube. A much larger increase in RMR was found with meal feeding (MF) as compared with tube feeding (TF). Measurements of respiratory quotient (RQ) indicated that the increase in RMR with MF is related to increased glucose oxidation, whereas with TF it is possibly explained primarily by the cost of energy storing. Determination of plasma norepinephrine (NE) indicated that the sympathetic nervous system is activated by MF but not by TF. Similarly, plasma glucose and insulin determinations have shown that the secretion of insulin is increased during food ingestion but only with the MF situation. Thus in the 30 min after the beginning of the meal, an increased glucose oxidation was observed that is possibly related to an enhanced NE and insulin secretion; such effects were nonexistent in the TF situation. These results would not substantiate the notion of the specific dynamic action of food and would indicate that independent of the composition of the ingested nutrients, the postprandial increase in RMR is also influenced by sensory and cognitive stimulations.