The influence of a visual and olfactory meal stimulus on plasma insulin, free fatty acids and glucose levels, was studied in six obese, nondiabetic young persons.
There was a significant increase in plasma immunoreactive insulin with a simultaneous decrease in plasma free fatty acids without demonstrable changes in plasma glucose. The observed rise in plasma immunoreactive insulin most probably is reflex in nature. However, all levels of the nervous system including cerebral cortex, reticular formation and hypothalamus, may play different roles in the facilitation or inhibition of such reflex. The participation of one or several of the gastrointestinal hormones, such as secretin or gastrin, could explain the delayed rise in plasma insulin. Dietary habits, appetite, palatability of the offered meal and a relaxed and tranquil patient seem to be essential factors to be taken into consideration, if success is to be achieved in this type of experimental study.