Study reveals scientific reason people have sweet tooths

By Mark Waghorn via SWNS

Having a sweet tooth is all down to "gut instinct", according to new research.

Cravings for chocolate, biscuits and soft drinks are fueled by cells in the intestine, say scientists.

They can tell the difference between real sugar and substitutes like Splenda or fructose better than taste buds.

The discovery could lead to new treatments for obesity, diabetes and other life-threatening conditions.

Added sugar intake has been linked to high blood pressure, inflammation fatty liver disease, heart attack and stroke.

Lead author Professor Diego Bohorquez, of Duke University, North Carolina, said: "We've identified the cells that make us eat sugar, and they are in the gut."

Infusing it directly into the lower intestine or colon does not have the same effect.

Added Prof Bohorquez: "We always talk about 'a gut sense,' and say things like 'trust your gut.' Well, there's something to this."

The sensing cells called neuropods are in the upper reaches, he explained.

They talk directly to the brain - changing eating behavior. The findings open the door to the development of medications that target them.

The cells communicate via synapses that connect neurons within milliseconds - using fast-acting neurotransmitter signals.

Prof Bohorquez said neuropods are sensory cells of the nervous system - like taste buds in the tongue or retinal cells in the eye that helps us see.

He said: "These cells work just like the retinal cone cells that are able to sense the wavelength of light.

"They sense traces of sugar versus sweetener and then they release different neurotransmitters that go into different cells in the vagus nerve, and ultimately, the animal knows 'this is sugar' or 'this is sweetener'."

In experiments, miniature organs grown in the lab from mouse and human cells represented the small intestine and duodenum, or upper gut.

Real sugar stimulated individual neuropods to release glutamate as a neurotransmitter.

Artificial sugar triggered the release of a different neurotransmitter, called ATP.

Using light therapy, or optogenetics, the scientists turned the neuropods on and off in the gut of a living mouse.

With their cells switched off, the animal no longer showed a clear preference for real sugar.

Prof Bohorquez said: "We trust our gut with the food we eat. Sugar has both taste and nutritive value and the gut is able to identify both."

The sweet taste receptor was first identified in the mouths of mice two decades ago.

Scientists attempted to knock them out - but found they could still somehow discern and prefer natural sugar to artificial sweeteners.

Prof Bohorquez and colleagues have finally solved the riddle - 20 years later.

Co-first author Dr. Kelly Buchanan, now at Massachusetts General Hospital, Boston, said: "Many people struggle with sugar cravings.

"Now we have a better understanding of how the gut senses sugars - and why artificial sweeteners don't curb those cravings.

"We hope to target this circuit to treat diseases we see every day in the clinic."

In future work, Prof Bohorquez said he will be showing how these cells also recognize other macronutrients.

He said: "We always talk about 'a gut sense,' and say things like 'trust your gut.' Well, there's something to this.

"We can change a mouse's behavior from the gut." It gives him great hope for new therapies targeting the gut, he added.

The study is in Nature Neuroscience.