Cephalic phase of insulin secretion and food stimulation in humans: a new perspective

Insulinemia and glycemia were measured at a 1-min interval at the hour of a lunch meal in human subjects. When no food was presented to naive subjects (n = 4), cyclic oscillations of insulinemia were found (period, 12-20 min; amplitude, 2.8-10.3 microU/ml). It is proposed that these spontaneous oscillations must be taken into consideration when evaluating the insulin response on cephalic contact with food stimuli; they might otherwise constitute a source of artifacts. Four subjects were then submitted to a series of four test meals scheduled at a 1-wk interval. Although their prandial glycemia remained comparable with preprandial values for the first 16 min of the meals, insulinemia often exhibited early peaks (within a few min after meal onset) whose amplitude appeared related to palatability conditions. Evidence suggests that the insulin peaks triggered by cephalic stimulation are Pavlovian reflexes that become conditioned to the test situation. A typical neuroendocrine response to alimentary frustration is also described. The results are discussed in perspective with animal works, in terms of the effects of neuroendocrine events on feeding behavior.