Researchers at the University of
Sydney have discovered the basic science of how sweet taste perception is
fine-tuned in response to different diets. While it has long been known that
food can taste different based on previous experience, until now we didn’t know
the molecular pathways that controlled this effect.
Professor Greg Neely at the Charles
Perkins Centre and School of Life and Environmental Sciences with Professor
Qiaoping Wang (formerly at the Charles Perkins Centre and now based at Sun
Yat-Sen University, China) used fruit flies to study sweet taste. They learned
that taste is highly subjective based on previous experience.
Professor Neely said they learned
four important things:
1. The food animals eat can change how
they perceive future food.
2. This response uses the same
machinery that the brain uses to learn
3. Pathways that can extend lifespan
were also involved in enhancing taste perception, and diets in fruit flies that
promote long life were also found to enhance taste perception.
4. Lifespan, learning and sensory
perception are linked in ways we are just starting to understand.
“We found that the fruit fly ‘tongue’
— taste sensors on its proboscis and front feet — can learn things using the
same molecular pathways that the fly brain uses to learn things. Central to
this is the neurotransmitter dopamine.
“It turns out these are also the
same chemical pathways that humans use to learn and remember all sorts of
things,” Professor Neely said. “This really highlights how learning is a
whole-body phenomenon; and was a complete surprise to us.”
Professor Wang, who led the study,
said: “We were surprised to find that a protein-restricted diet that makes an
animal live much longer also turns up the intensity of sucrose perception for
that animal, and that is dependent on the same learning and longevity pathways.
“The response was also really
specific. For example, when we fed flies food that had no sweetness, the
animals’ sweet taste perception was enhanced, but only for glucose, not for
fructose. We have no idea why they specifically focus just on one kind of sugar
when they perceive them both as sweet.”
“We also found that eating high
amounts of sugar suppressed sweet taste perception, making sugar seem less
sweet,” Professor Neely said. “This finding, which occurs through a different
mechanism, matched nicely with recent results from our colleague Monica Dus at
the University of Michigan, who is the world expert in this area.”
Taste study
The researchers found if they
changed the diet of the fruit fly (increasing sugar, removing taste of sugar,
increasing protein, changing sugar for complex carbohydrate), this drastically
altered how well the fruit fly could taste subsequent sugar after a few days.
Flies normally live about 80 days in optimal circumstances.
“We found that when flies ate
unsweetened food, this made sugary food taste much more intense,” Professor
Wang said.
“Then we looked at all the proteins
that changed in the fruit fly ‘tongue’ in response to diet, and we investigated
what was happening,” Professor Neely said.
They found the sensation of taste is
controlled by dopamine (the “reward” neuromodulator). The researchers then
mapped the pathway and found the same pathways that are well established as
controlling learning and memory or promoting long life also enhance taste
sensation.
“While this work was conducted in
fruit flies, the molecules involved are conserved through to humans. We know
humans also experience changes in taste perception in response to diet, so it’s
possible the whole process is conserved; we will have to see,” Professor Wang
said.
The research
published in Cell Reports, is a follow up study
to Professor’s Neely’s work testing the effects of artificial sweeteners in
humans. That research found artificial sweeteners activate a neuronal
starvation pathway, and end up promoting increased food intake, especially when
combined with a low-carb diet.
“Our first studies were focused on
how different food additives impact the brain, and from this we found taste
changed in response to diet, so here we followed up that observation and
describe how that works,” Professor Neely said. “Turns out the fly ‘tongue’
itself is remembering what has come before, which is kind of neat.”
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