Abstract
The present study focused on the oral stimulatory effect (cooling sensation) of carbonated water. In order to determine the degree to which consumption of carbonated water changes body temperature, and whether such a reaction can occurs through oral stimulation alone, we conducted feeding and sham-feeding (SF) tests employing identical temperatures and volumes of carbonated water and plain water. We conducted 4 types of tests (carbonated water consumption [CW], plain water consumption [W], carbonated water sham-feeding [CW-SF], and plain water sham-feeding [W-SF]) with a randomized crossover design. Thirteen young women began fasting at 10：00 pm on the previous night and samples of water were ingested (15℃, 250 mL) at 9：00 am on different days in a laboratory where the temperature was maintained at 26℃. Electrocardiograms were obtained 20 min before and 40 min after sample ingestion. The subjects’ core (eardrum) and peripheral (foot) temperatures were monitored continuously using highly sensitive thermosensors. The eardrum temperature did not change in the W-SF and CW-SF groups, but showed a temporary decrease in the W and CW groups. Foot temperature decreased by approximately 2.5-3℃ in the W and CW groups. Furthermore, while foot temperature decreased by approximately 1℃ in the W-SF group, a decrease of approximately 2.5℃ was observed in the CW-SF group. Heart rate increased temporarily immediately after the end of ingestion in the CW and CW-SF groups. These results suggest that oral stimulation by carbonic acid is solely responsible for changing the heart rate and peripheral temperature.
