Our tongues apparently recognize and have an affinity for fat, 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 Journal of Lipid Research.
found that people with a particular variant of the CD36 gene are far
more sensitive to the presence of fat than others.
goal is to understand how our perception 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
The researchers studied 21 people with a body mass index
(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.
“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
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 fatty foods. 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
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 taste 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 fatty acids 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
Pepino MY, Love-Gregory L, Klein S, Abumrad NA, The fatty acid
translocase gene, CD36, and lingual lipase influence oral sensitivity to
fat in obese subjects. Journal of Lipid Research, Dec. 31, 2011 [Epub
ahead of print].
Funding for this research comes from the National Center for Research
Resources and the National Institute of Diabetes and Digestive and
Kidney Diseases of the National Institutes of Health (NIH), and by a
grant from GlaxoSmithKline Consumer Healthcare Research Program.
Washington University School of Medicine’s 2,100 employed and volunteer
faculty physicians also are the medical staff of Barnes-Jewish and St.
Louis Children’s hospitals. The School of Medicine is one of the leading
medical research, teaching and patient care institutions in the nation,
currently ranked fourth in the nation by US News & World Report.
Through its affiliations with Barnes-Jewish and St. Louis Children’s
hospitals, the School of Medicine is linked to BJC HealthCare.This article was first published at www.newswise.com