Receptor for tasting fat identified in humans (w/ Audio)

Scientists already knew the tongue could sense five distinct tastes but disagreed about over whether taste buds could detect fat. New research finds the tongue recognizes fat and that variations in a gene make people more or less sensitive to the taste of fat in foods. Credit: Washington University School of Medicine

Why do we like fatty foods so much? We can blame our taste buds.

Our tongues apparently recognize and have an affinity for , according to researchers at Washington University School of Medicine in St. Louis. They have found that variations in a gene can make people more or less sensitive to the taste of fat.

The study is the first to identify a human receptor that can taste fat and suggests that some people may be more sensitive to the presence of fat in foods. The study is available online in the .

Investigators found that people with a particular variant of the CD36 gene are far more sensitive to the presence of fat than others.

"The ultimate goal is to understand how our of fat in food might influence what foods we eat and the quantities of fat that we consume," says senior investigator Nada A. Abumrad, PhD, the Dr. Robert A. Atkins Professor of Medicine and Obesity Research. "In this study, we've found one potential reason for individual variability in how people sense fat. It may be, as was shown recently, that as people consume more fat, they become less sensitive to it, requiring more intake for the same satisfaction. What we will need to determine in the future is whether our ability to detect fat in foods influences our fat intake, which clearly would have an impact on obesity."

People who made more CD36 protein could easily detect the presence of fat. In fact, study subjects who made the most CD36 were eight times more sensitive to the presence of fat than those who made about 50 percent less of the protein.

The researchers studied 21 people with a (BMI) of 30 or more, which is considered to be obese. Some participants had a genetic variant that led to the production of more CD36. Others made much less. And some were in between.

Participants were asked to taste solutions from three different cups. One contained small amounts of a fatty oil. The other two contained solutions that were similar in texture to the oil but were fat-free. Subjects were asked to choose the cup that was different.

This video is not supported by your browser at this time.
Washington University researchers are the first to identify a potential human receptor for tasting fat. In a series of taste tests, they've found that people can identify fat in a liquid solution and that their ability to identify fat changes according to how much of a particular receptor protein they manufacture. Jim Dryden reports. Credit: Washington University BioMed Radio

"We did the same three-cup test several times with each subject to learn the thresholds at which individuals could identify fat in the solution," explains first author M. Yanina Pepino, PhD, research assistant professor of medicine. "If we had asked, 'does it taste like fat to you?' that could be very subjective. So we tried to objectively measure the lowest concentration of fat at which someone could detect a difference."

Her team masked input that might help participants identify fat by sight or smell. To eliminate visual cues, they lit the testing area with a red lamp. Study subjects also wore nose clips so that they could not smell the solutions.

Fat is an important component of the diet, and both humans and animals usually prefer high-fat, energy-dense foods. Scientists have believed that people identify those high-fat foods mainly by texture, but this study suggests that the presence of fat can change the way our tongues perceive the food, just as it does for the tastes sweet, sour, bitter, salty and savory (umami).

The CD36 discovery follows research that had identified a role for the gene in rats and mice. Scientists had learned that when animals are genetically engineered without a working CD36 gene, they no longer display a preference for . In addition, animals that can't make the CD36 protein have difficulty digesting fat.

Up to 20 percent of people are believed to have the variant in the CD36 gene that is associated with making significantly less CD36 protein. That, in turn, could mean they are less sensitive to the presence of fat in food.

Abumrad was the first to identify CD36 as the protein that facilitates the uptake of fatty acids. She says better understanding of how the protein works in people could be important in the fight against obesity.

People with obesity are at an elevated risk for cardiovascular disease, stroke, type 2 diabetes, certain cancers, arthritis and other problems. Obesity rates have risen dramatically over the past 30 years as more people have become sedentary, and diets incorporate more hamburgers, French fries, fried chicken and other high-fat foods.

"Diet can affect sensitivity to fat, and in animals, diet also influences the amount of CD36 that's made," Pepino says. "If we follow the results in animals, a high-fat diet would lead to less production of CD36, and that, in turn, could make a person less sensitive to fat. From our results in this study, we would hypothesize that people with obesity may make less of the CD36 protein. So it would seem logical that the amounts of the protein we make can be modified, both by a person's genetics and by the diet they eat."

Our diet contains fat, mainly in the form of triglycerides, which are made of fatty acids linked to glyerol. In the tast test, the researchers presented subjects with two types of fat. Some cups contained a free fatty acid. Others contained triglyerides.

Pepino and Abumrad knew from animal studies that CD36 is activated by fatty acids but not triglycerides. Human subjects, however, were able to taste both. Pepino believes that's probably due to the activity of an enzyme called lipase in the saliva that breaks the triglycerides, releasing the fatty acids while the fat is still in the mouth.

"Rats, for example, can produce salivary lipase, and the lipase quickly will begin to digest the triglyceride and convert it into a fatty acid," she explains. "In humans, the role of lipase hasn't been as clear. In our experiments, people could detect fat whether it was a triglyceride or a fatty acid."

But when the researchers added the diet drug orlistat, subjects could still taste the but were less able to detect the triglycerides. Orlistat inhibits lipase in the mouth, stomach and intestine and is often prescribed to people who are obese to prevent them from absorbing fat in foods.

"Orlistat made it more difficult for people to taste fat," Pepino says. "The solution had to contain higher amounts of triglyceride before they could detect fat. With free fatty acid, however, there was no difference."

Related Stories

Australian researchers say fat is 'sixth taste'

Mar 08, 2010

It's a theory set to confirm why humans are so fond of fatty foods such as chips and chocolate cake: in addition to the five tastes already identified lurks another detectable by the palate -- fat.

Obesity is associated with reduced sensitivity to fat

Jul 13, 2010

Research to be presented at the Annual Meeting of the Society for the Study of Ingestive Behavior (SSIB), the foremost society for research into all aspects of eating and drinking behavior, finds marked differences between ...

Fat substitutes linked to weight gain

Jun 20, 2011

Synthetic fat substitutes used in low-calorie potato chips and other foods could backfire and contribute to weight gain and obesity, according to a study published by the American Psychological Association.

Do low-fat foods make us fat?

Dec 08, 2006

Recent Cornell studies in movie theatres, holiday receptions, and homes showed people eat an average of 28% more total calories when they eat low-fat snacks than regular ones. "Obese people can eat up to 45% more," reports ...

Recommended for you

Unlocking the secrets of pulmonary hypertension

14 hours ago

A UAlberta team has discovered that a protein that plays a critical role in metabolism, the process by which the cell generates energy from foods, is important for the development of pulmonary hypertension, a deadly disease.

User comments

Adjust slider to filter visible comments by rank

Display comments: newest first

MP3Car
not rated yet Jan 12, 2012
the image associated with this article probably will perpetuate the myth that different areas of your tongue are used for only certain tastes...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.