Relationship between taste-induced physiological reflexes and temperature of sweet taste.

Excessive consumption of soft drinks has been argued as a key contributor to the epidemic of obesity in modern society. This is because they are characterized by high content of sugar, low satiety, and incomplete compensation for total energy. However, since obesity involves complex interactions of various factors, there must be more indices to link soft drink consumption and development of obesity. In this study, we have concentrated on the taste component of soft drinks and how they are consumed. We particularly investigated the temperature dependence of the indices associated with glucose metabolism such as cephalic phase insulin release and sympathetic nerve activity (SNA) of brown adipose tissue (BAT) to sweet solution since soft drinks are usually consumed in very cold temperature. Glucose solution incubated at room temperature (warm; 25 degrees C) or refrigerated to 4 degrees C (cold) was administered to the rats and significant rise in plasma insulin was observed at 3rd min in warm group while it was not increased until 15th min in cold group. The initial rise in plasma insulin did not coincide with a rise in blood glucose in warm group. Under the anesthesia, warm glucose solution significantly enhanced SNA of BAT while cold glucose solution exhibited no difference. The nerve response of chorda tympani also showed greater response to warm glucose solution than cold glucose solution. These results suggest that cold sweet taste stimulus does not accompany expected taste-induced physiological reflexes, possibly retarding organisms' energy expenditure system.