Chewing the fat - and tasting it, too

For years, we've considered "chewing the fat" more rewarding in metaphor than in sensory reality. But a new study by Richard Mattes, professor of food and nutrition at Purdue University in West Lafayette, Ind., says fat has a taste after all, perhaps explaining why fat-free foods often just don't match the gustatory glee of their full-fat counterparts.

Scientists have long insisted that fat, on its own, has no taste, but is merely a flavor carrier, enhancing foods by adding texture ("mouth feel") and delivering odor. Now, Professor Mattes's findings make fat sensation the sixth basic taste, in addition to salty, sweet, sour, bitter, and unami, a sense awakened by monosodium glutamate (MSG) in foods.

The idea that we might taste fat has slithered around since the 16th century, but because modern scientists found no means of fat detection, they brushed the notion aside. Many were unmoved even when studies found rats' taste cells registering electrical changes in response to fat; they clung instead to primate research, which posited that we discover fat only by smelling it.

But Mattes wasn't entirely convinced. From previous studies, he was confident that human chemical detection of fat existed, because blood fat levels change when fat touches human mouths. But he wasn't sure if the chemical shift was olfactory or gustatory.

In Mattes's study, subjects munched cream cheese on crackers. Some wore nose plugs blocking their senses of smell; some could only smell the fat; others tasted and smelled. A control group got no snack.

As expected, blood fat levels in the group that munched and sniffed the cream cheese rose more than those in the unfed control group - three times as much, in fact. The surprise came when subjects wearing nose plugs - and thus merely tasting the fat - showed blood-level increases just as marked as those of subjects who tasted and smelled cream cheese, implying smell wasn't crucial after all. Those who only smelled the fat showed no increase in blood-fat levels.

Mattes's findings, if confirmed, may revolutionize gustatory knowledge. The search for fat substitutes could take a new twist, and textbooks would have to be revised. And in the conundrum of low-fat, low-satisfaction foods, this new discovery would really be something to chew on.