As any chef at a greasy spoon can attest, humans have a taste for fatty foods. Now, scientists may know why. Researchers have found a new receptor on mice and rat tongues that detects fat and helps prepare the body to digest it. The results may help explain why some people crave fat more than others and could help researchers uncover new ways to fight obesity.
It's long been clear that humans and rodents taste sweet, sour, bitter, salty, and protein-rich foods, but researchers thought we sensed the fat in food by its smell and creamy texture. Over the past decade or so, however, results have dribbled in suggesting we--or at least mice and rats--taste fats. In one study, applying a chemical to the tongue that blocks a fat-digesting enzyme prevented rats and mice from tasting fats and fatty acids, a breakdown product of fats.
Intrigued, physiologist Philippe Besnard of the University of Bourgogne in Dijon, France, and colleagues focused on a fatty-acid receptor called CD36 that's found in fat and other tissues. After chemically linking a red fluorescent dye to antibodies that bound CD36, the researchers showed that taste buds glowed red, indicating that CD36 was in the right place to do the job.
To see if animals use CD36 to taste fats, the team bred a line of mice that lacked the receptor. When given a choice between their standard fare and fat-enriched treats, normal mice consumed 3 times as much of the junk food, but mutant mice showed no preference, presumably because they couldn't taste the difference.
The taste bud receptors send a signal when they sense fat. The researchers learned this by applying fatty acids to the tongues of mice that had their digestive tracts tied off to prevent ingestion. Normal mice--but not those lacking the CD36 receptors-- immediately cranked up their production of bile, which breaks down fats, the researchers report in the November issue of the Journal of Clinical Investigation. The results indicate that CD36 helps relay a signal to the digestive system, telling it to get ready to digest fats; receptors that taste sweetness relay similar signals.
Because genetic variants of CD36 exist in humans, studies of the receptor in humans could help explain why some people crave fat more than others do. Scientists could potentially uncover compounds that block CD36, which could cut fat cravings and combat obesity, says biochemist Nada Abumrad at Washington University School of Medicine in St. Louis, Missouri. That's still in the future, but the research is a good start, she says. "The work was very well done."