The Route to Obesity Passes Through Your Tongue

According to neuroscientists, obesity gradually numbs the taste sensation of rats to sweet foods, and drives them to consume larger and sweeter meals. There is apparently a critical link between taste and body weight.
Previous studies have suggested that obese persons are less sensitive to sweet taste, but little is known about the specific differences in sense of taste between obese and lean individuals. Researchers investigated these differences by studying the taste responses of two strains of rats.
Compared to the lean and healthy LETO rats, the taste responses in OLETF rats mirror those in obese humans. These rats tend to chronically overeat due to a missing satiety signal, and they become obese and develop diabetes. The obese rats also show an increased preference for sweet foods.
The researchers implanted electrodes in the rodents' brains to record the firing of nerve cells when the rats' tongues were exposed to various tastes. The OLETF rats had about 50 percent fewer neurons firing when their tongues were exposed to sucrose, suggesting that obese rats are overall less sensitive to sucrose.
Sources:
Science Daily November 26, 2008