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Fatty food triggers taste buds, new research finds

WEST LAFAYETTE, Ind. – It wasn't your imagination that the fat-free chocolate chip cookie dough ice cream didn't taste as good as the creme de la creme version, despite what the label said.

Your no-guilt taste treat was indeed lacking in taste. Contrary to current scientific dogma, fat does have taste after all, according to Purdue University research.

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."

Writer: Steve Tally, (765) 494-9809; tally@aes.purdue.edu

Source: Richard Mattes, (765) 494-0662; mattesr@cfs.purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Note to journalists: The citation for the article mentioned in this story is R.D. Mattes, The taste of fat elevates postprandial triacylglycerol. Physiology & Behavior 74 (2001) 343-348. A copy of the paper is available from Purdue Agricultural Communications, (765) 494-9809.

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


ABSTRACT

The taste of fat elevates postprandial triacylglycerol

Richard Mattes, Purdue University

Recent evidence suggests there may be a chemosensory component to fat perception. This study explored the independent contributions of taste and smell stimulation by dietary fat on the postprandial rise of serum triacylglycerol (TAG). Nineteen healthy adults participated in four test sessions. Treatments were presented in random order and consisted of lipid loading (50g safflower oil in capsules) followed by oral (i.e., taste and smell) or odor-only stimulation with cream cheese on crackers or no load with odor or no stimulation. In a fifth session, attended by eight participants, lipid loading was followed by taste-only stimulation. Blood was collected from overnight fasted participants followed by lipid ingestion (10 minutes) and another blood collection 20 minutes later. Oral stimulation was then initiated (where applicable) at three minute intervals for 60 minutes and 15 minute intervals for an additional 60 minutes. Blood was drawn again 2, 4, 6 and 8 hours after initiation of oral stimulation. Fat loading with oral stimulation led to serum TAG concentrations that were significantly elevated over baseline at the 2, 4, and 6 hour time points. Fat loading with odor stimulation led to a significant rise only at the f hour time point. No significant elevation was observed with either no-load treatment. Only the TAG UAC value after oral exposure was significantly elevated compared to baseline (t=4.35, p<0.001). The increase in TAG concentration with fat loading and oral stimulation was also greater than the response to other treatments. Taste-only treatment led to a significantly higher TAG response than all other treatments except loading with oral stimulation. TAG responses to oral stimulation and taste-only stimulation were significantly correlated (r8=0.92, p=0.01) six hours postprandially. These data provide additional evidence supporting a taste component for human fat perception.


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