Fatty Food Triggers Taste Buds, New Research Finds

For decades scientists agreed on four basic food tastes: sweet, salty, sour and bitter. In recent years, scientists also have agreed on a fifth sense, umami, which is evoked by monosodium glutamate (MSG) in foods.

Nutritionists and other scientists have said for years that fat only provides texture to foods, and that pure fat itself doesn't have any taste. Fat has been thought to be a flavor carrier that could deliver taste and odor compounds derived from different parts of food, and as a component that provided texture and what food scientists call "mouth feel" in foods.

But new research by Richard Mattes, professor of foods and nutrition, indicates that humans can indeed taste fat, which would mean that ability is a sixth basic taste.

The finding is more than a physiological curiosity: It also could explain why fat-free foods aren't as popular as full-fat versions.

"I wonder if the less-than-perfect performance of current fat replacers may be due to a lack of understanding of all mechanisms for fat perception," Mattes says. "Failure to account for a taste component may compromise quality."

In the 1500s the idea that humans could taste fat was proposed by the French physician and philosopher Jean Fernell (who is remembered for coining the term physiology). Modern scientists didn't believe this was possible, however, because there was no mechanism to detect fat.

Recent studies with rats began to cast doubt on that idea. Studies have shown that fats were capable of causing electrical changes in taste cells of rats, indicating there was a chemical detection system there.

"Studies in mice and rats also have shown that in carefully controlled taste tests — ones so brief that there's no metabolic feedback, and, using taste solutions, one so dilute that there's a minimal textural component — rats easily detect and prefer the foods with fat," Mattes says.

Some scientists still believed fat had no taste and hypothesized that animals and perhaps people detect fat by smelling it. Studies in primates indicated that was the case.

Mattes and his graduate students decided to determine if humans were tasting fat or merely smelling it. "Our initial hypothesis was that odor was responsible," he says.

Previous studies by Mattes had shown that blood fat levels were changed in humans just by putting fat in their mouths.

"That suggested to us that there was some sort of chemical detection, but we didn't know if it was a taste or an odor. There are studies with monkeys smelling cream that show odor alone causes neurons in the brain to be activated. In general, with humans, if you pinch the nose, a person's ability to detect fats declines. In rats, if you damage the nerves that respond to odors, their ability to detect fats declines."

In the study, subjects had their blood fat levels checked before and after the test. The test used cream cheese on crackers to determine if people could taste fat. Some people were allowed to taste and smell fat; some were only allowed to taste or smell fat, but not both (some were wearing nose plugs), and there was a control group that received no sensory stimulation at all.

The study found that blood fat levels in the group that had been allowed to taste and smell the fat rose three times more than the control group. However, the study also found that blood levels rose as much in people who were wearing nose plugs as in people who could both taste and smell the cream cheese. Blood fat levels didn't rise in people who could only smell the cream cheese but not taste it.

"This tells us that taste is the stimulus that causes the rise in blood fat levels. The taste, and not the smell, is what the body is responding to," Mattes says.

If further studies confirm Mattes' findings, textbooks have to add fat to the list of taste sensations, food scientists would have to revise their recipes and other areas of science would be influenced as well.

For example, biologists have theorized about the evolution of taste and how it allowed humans to find and evaluate potential sources of nutrients. However, these discussions have left out fat because it was assumed there were no taste or odor receptors for it. That may have to change, Mattes says.

"The ability to taste fat could hold evolutionary advantages in the ability to absorb essential fatty acids from food."