No matter how cleverly prepared, fat-free foods never seem satisfying. Now we know why. Nutritionist Philippe Besnard of the University of Burgundy in France has found that the 10,000 taste buds on the tongue seem to include a type that specifically responds to the flavor of fat. If confirmed, it would be only the sixth known type, joining those that sense sweet, salty, sour, bitter, and savory (also known as umami).
Besnard uncovered the fat sensor in the tongues of genetically engineered mice that lacked the ability to make a protein called CD36. Mice normally have a yen for fatty foods, but the altered animals showed no preference for the stuff. Furthermore, regular mice release fat-digesting secretions in their bowel and ramp up intestinal fat absorption as soon as they taste fat; the modified mice displayed no such response. Apparently, CD36 is the key protein that allows certain mouse taste buds to respond to fat. Humans, whose sense of taste works almost exactly like that of mice, almost certainly have the same taste bud.
From an evolutionary perspective, having a fat bud is a big advantage. It causes animals to crave and consume high-calorie fatty foods and then prompts their bodies to quickly and efficiently digest the fats, storing away an energy reserve for times of starvation. If scientists can find a way to develop nonfattening foods that latch onto the fat receptors, they may be able at long last to develop fat-free snacks that can actually trick the tongue.