November 1, 2005
Tongue Has Built-In Taste for Fatty Food
By Amy Norton
NEW YORK -- The tongue may indeed have a taste for cheesecake, french fries and butter cookies, according to study published Tuesday.
In experiments with rodents, French scientists identified a receptor on the tongue that appears to detect dietary fat. This counters the traditional view that the taste buds pick up only five basic flavors: sweet, sour, salty, bitter and "umami," -- a flavor associated with the food additive monosodium glutamate (MSG).
The fact that the tongue harbors receptors for fatty acids could shed new light on appetite control and obesity, according to the researchers, led by Philippe Besnard of the University of Bourgogne.
They report their findings in the November issue of the Journal of Clinical Investigation.
Scientists have speculated that the tongue may have a receptor designed to detect fat, but this study is the first to pinpoint one, according to Besnard and his colleagues. The receptor, a protein called CD36, is already known to exist in many tissues and is involved in fat storage, among other jobs; it is also goes by the name of fatty acid transporter, or FAT.
Rats and mice, not to mention many humans, have a natural preference for fatty food, and rats have already been shown to have CD36 proteins in their taste buds.
To see whether CD36 might be the tongue's fat detector, Besnard and his colleagues studied rats and mice that were either normal or had the gene for CD36 "knocked out," inactivating the protein.
They found that while the genetically normal animals naturally opted for fattier fare when given the choice, the CD36-deficient mice had no such preference. And when the researchers put fatty acids on the tongues of the normal animals, this alone triggered a release of fat-processing substances from the digestive organs. Again, the same was not true of mice lacking CD36 activity.
Though the body's regulation of fat intake is complex, these findings point to the importance of CD36 receptors on the tongue, Besnard told Reuters Health.
It's possible, he speculated, that the receptor's effects -- encouraging a preference for fat and launching a quick release of digestive substances -- conferred an evolutionary advantage when food was scarce. In modern times of plenty, however, this may be a disadvantage for the waistline.
Some past studies, Besnard and his colleagues note, have shown that obese people have a greater preference for fatty food than leaner individuals do -- which, they say, suggests that dysregulation in fat "perception" may play some role in obesity.
Research over the years has already shown that individuals vary widely in their ability to perceive different flavors, and inherited differences in taste receptors are thought to be involved. Experts estimate that while half of Americans are "medium" tasters, the rest are divided equally into "nontasters," who barely perceive one or more flavors, and "supertasters," who find some flavors too intense.
It's not clear yet how this all factors into eating habits and body weight. But it's "not unreasonable" to suggest that individual differences in CD36 play a role in fat perception, and possibly weight control, according to Nada A. Abumrad of Washington University School of Medicine in St. Louis.
"As more is learned about the specificity and mechanism of this receptor's function," Abumrad writes in a commentary, "it may be possible to devise strategies to treat some forms of obesity."
SOURCE: Journal of Clinical Investigation, November 2005.