APR 15, 2020 1:09 PM PDT

Sugar's Appeal Lies in a Circuit That Connects the Gut & Brain

WRITTEN BY: Carmen Leitch

When we consume sweet, sugary foods, it activates taste buds on the tongue. We also know that sugar has a powerful effect on the brain; new research may help explain why that happens. Scientists have shown that sugar can trigger a neurological pathway that starts in the gut and goes straight to the brain. The work has been reported in Nature.

Scientists led by Howard Hughes Medical Institute Investigator Charles Zuker found that in a mouse model, when sugar hits the intestines, signals are sent to the brain, where they promote cravings for more sugar. Experiments showed that this pathway only responded to sugar, not artificial sweeteners.

Zuker's group showed in 2008 that even when mice cannot sense sweet tastes, they still prefer sugary foods. This work may show why sugar has a unique effect and why it's so hard to satisfy sugar cravings.

"We need to separate the concepts of sweet and sugar," noted Zuker, a Columbia University neuroscientist. "Sweet is liking, sugar is wanting. This new work reveals the neural basis for sugar preference."

Sugar is a term used to describe a variety of chemicals that have a sweet taste, provide the body with energy, and activate mechanisms in the brain that make humans and mice feel good. That leads people to seek out sugary foods, which were once only available in limited quantities. But in the modern world, people can choose to consume vast quantities of sugar, which has also been added to myriad processed foods. In the late 1880s, the average American ate about ten pounds of the stuff in a year; that average has now risen to over 100 pounds. It's no surprise that metabolic diseases have also grown far more common.

While sugars and artificial sweeteners both activate the same system that senses sweet tastes, sugar has a behavioral effect that artificial sweeteners don't seem to have.

When the researchers gave mice a choice between the water spiked with the sweetener Acesulfame K (which is added to diet soda) or sugar, the mice started out consuming both but within two days, were selecting sugar water almost exclusively.

A region of the mouse brain known as the cNST (colored yellow at top) responded to the presence of sugar, even if it was infused directly into the gut. / Credit: Tan et al./Nature 2020

"We reasoned this unquenchable motivation that the animal has for consuming sugar, rather than sweetness, might have a neural basis," Zuker said.

The scientists observed brain activity after mice consumed sugar or the artificial sweetener, and identified a brain region that is responsive only to sugar. This area is called the caudal nucleus of the solitary tract (cNST), and is in the brain stem, separate from the area where taste is sensed. The cNST acts as a hub of information about the body's state. The scientists found that in the lining of the intestine, when sugar is sensed, a signal is sent from the vagus nerve directly to the brain.

This direct pathway from the gut to the brain prefers sugar in the form of glucose, and some other chemicals that are similar. Artificial sweeteners don't stimulate the circuit, which may explain why they can't fully displace sugar in the marketplace. Fructose, which is found in fruits, is also ignored by the pathway.

Though these studies were conducted in mice, Zuker is confident that a pathway that is essentially the same also exists in humans.

"Uncovering this circuit helps explain how sugar directly impacts our brain to drive consumption," he said. "It also exposes new potential targets and opportunities for strategies to help curtail our insatiable appetite for sugar."

Image credit: Pixabay

Sources: AAAS/Eurekalert! via Howard Hughes Medical Institute, Nature

About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
AUG 01, 2021
Drug Discovery & Development
Berry Compound Reverses Parkinson's in Mice
AUG 01, 2021
Berry Compound Reverses Parkinson's in Mice
A naturally-occurring compound called farnesol found in berries and other fruits prevents and reverses Parkinson's-a ...
AUG 03, 2021
Genetics & Genomics
Aging Cells May Lose Control of Where an mRNA Sequence Starts
AUG 03, 2021
Aging Cells May Lose Control of Where an mRNA Sequence Starts
When a gene is active, it's transcribed from DNA to RNA, and a specific sequence in the genetic code acts like a sig ...
AUG 08, 2021
Cell & Molecular Biology
How Stress Can Impact Gene Expression in the Brain
AUG 08, 2021
How Stress Can Impact Gene Expression in the Brain
University of Bristol researchers have learned more about how chronic stress may be linked to health problems, both phys ...
AUG 11, 2021
Genetics & Genomics
Was This Medieval Warrior Non-Binary?
AUG 11, 2021
Was This Medieval Warrior Non-Binary?
Scientists have now learned more about a burial site unearthed at Suontaka in Finland in 1968 that contained two swords, ...
AUG 27, 2021
Health & Medicine
Blood Group and COVID-19 Susceptibility- An Ongoing Debate
AUG 27, 2021
Blood Group and COVID-19 Susceptibility- An Ongoing Debate
Since their discovery, there has been an interest in how ABO blood groups and infectious diseases may be related. In add ...
SEP 02, 2021
Microbiology
Microbes Create an Electrical Grid in Nature
SEP 02, 2021
Microbes Create an Electrical Grid in Nature
The world is full of single-celled organisms, which can be found virtually everywhere from hydrothermal vents in the dee ...
Loading Comments...