Subject: High Yuck Factor Not Necessarily Good for Us Anymore
Monday, July 25, 2005
Modern humans who were better able to discern bitter flavors
in
plants that signaled poisonous fare had a competitive advantage
by
the time they began moving out of Africa to the corners of
the world.
But now, this sensitivity may have given much of mankind such
a sweet
tooth that we tend to avoid bitter-tasting foods that may contain
nutrients that are important to reducing the risk of cancer
and heart
disease, researchers suggest in a new study published Tuesday.
The report in the journal Current Biology shows that a variant
of a
gene that encodes for a taste receptor mainly responsible for
identifying bitterness became widespread in humans between
800,000
and 100,000 years ago, before the mass migration of early people
out
of Africa.
Scientists led by Nicole Soranzo of University College London
and
David Goldstein of the Duke University for Genome Sciences
and
Policy, formerly of the University College, analyzed genetic
material
from 997 individuals representing 60 human populations from
all over
the world to reconstruct the history of the gene that appears
to make
most people so sensitive to bitter tastes.
The human sense of taste is generally far less refined than
that of
other primates and mammals, Goldstein said, but added that
the
prevalence of the gene variant shows that having specific sensory
abilities may have been particularly important in the early
stages of
human evolution, when small groups of hunter-gatherers lived
entirely
off the land.
Since the late Stone Age, humans have been processing foods
by
soaking, baking or boiling in ways that inactivate toxins in
them so
that "it is generally thought that the ability to recognize
compounds
through the sense of taste is less important for people than
it is
for other animals," Soranzo said.
But the prevalence of the receptors for bitter taste "suggests
that
sensory detection of dangerous foods played an important role
at
certain times during the course of our evolution,'' she added.
That may have been particularly true when early humans moved
out of
established territories into new environments in Africa and
then on
into the Middle East, Europe and Asia, where they had to rely
on
their taste buds to know whether new plant species were safe
to eat
or had to be avoided.
In particular, one of the gene variants the scientists found
gives
taste bud receptors an increased sensitivity to certain toxins,
including five that release cyanide when digested, the researchers
found. This taste receptor, called TAS2R16, is also more sensitive
to
certain beneficial compounds in plants when it has a particular
variant form, the scientists showed.
Cyanide-releasing compounds are widely used as protection by
both
plant and insect species around the world, and for most animals,
one
dose is lethal. But researchers have also found that constant
exposure to less-than-lethal amounts of the compounds is tolerated,
particularly when humans and other animals eat a diet high
in
protein.
Moreover, Soranzo said not everything bitter is bad for us.
Some,
notably salicin and arbutin, are known to lower the risk of
cancer
and heart disease, yet "owing to their bitter taste, these
compounds
are routinely removed by the food industry and represent a
key
limitation in increasing the nutrient content of plant foods. "
While this gene variant may have helped to avoid natural toxins
in
our past, one might speculate that it may now contribute to
increasing disease risk through lowered intake of such beneficial
compounds,'' Soranzo said.
Significantly, the researchers also noted that human populations
in
much of Africa still have a genetic receptor for bitter taste
that's
slightly less sensitive, apparently because eating low levels
of
cyanide-releasing foods offers some protection against malaria.
On the Net: http://www.current-biology.com
http://www.nlm.nih.gov/medlineplus/news/fullstory_25969.html
(*this news item will not be available after 08/24/2005)
Scripps Howard News Service
