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Gut clock regulates when we're hungry

Certain nerves in the stomach act as a kind of biological clock, which may help dampen appetite at night and allow heartier eating during the day, researchers have found.

The results, published today in The Journal of Neuroscience, may help shed some light on why shift workers are at high risk of conditions like obesity and diabetes, they say.

Stephen Kentish and colleagues from the University of Adelaide's Nerve-Gut Research Laboratory studied a particular set of nerves in the muscular layers around the stomachs of laboratory mice.

A major role of these nerves is to help animals know how full they are.

"They send signals back from the stomach to provide feelings of fullness based on the distension of the stomach," says Kentish.

The researchers wanted to explore how the responses of these nerves varied in the course of a 24-hour period.

To do this, they measured nerve activity when mouse stomach walls were stretched at three-hourly intervals between 6 am and 3 am the following day.

They found that the nerves were least sensitive to the stomach's stretching at times when the mice were normally awake.

This seems logical, they say, as reduced sensitivity would allow the animals to fill their stomachs at times when they would need more energy.

On the other hand, during times when the mice would normally be sleeping, the nerves in the stomach became much more sensitive. This meant that the brain received a signal of fullness more quickly, shutting down the desire to eat.

"This variation repeats every 24 hours in a circadian manner, with the nerves acting as a clock to coordinate food intake with energy requirements," Kentish says.

Following on from this work, the researchers also found that these nerve cells expressed a set of "circadian clock" genes that are also expressed in the brain region that regulates the wider circadian rhythm of the body.

In other words, the researchers say, these nerve cells appear to form a kind of neural clock in the stomach, regulating the amount of food needed to elicit fullness during the day and night.

Shift workers

Although the experiment was conducted in mice, the researchers expect that the same system would operate in the human stomach, with the gut nerves being less sensitive to fullness during the day and more sensitive at night.

"I would speculate that a similar effect would occur in humans," says Kentish.

What's more, the researchers think their research could shed light on why changes in people's circadian clocks affect their eating habits.

"We know that metabolic conditions such as obesity and diabetes are much more prevalent in shift workers and people who don't have a fairly consistent light-dark cycle," says Kentish.

And exploring the causes of these problems is the next step for the Adelaide team, he says. "We want to see how these systems can be disrupted by shift work and obesity."