http://news.yahoo.com/s/nm/20051101/hl_nm/tongue_built_in_taste_fatty_food_dc

"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)."