Study of link between night eating and the peculiar internal clock of fat cells

December 4, 2012 by Stacey Burling

When researchers at the University of Pennsylvania messed with the internal clocks of mouse fat cells, a surprising thing happened. The mice got fat.

Figuring out why led to more surprises. Mice usually eat at night, but the altered mice ate more of their food during the day. They got fat even though they ate the same number of calories as regular, nocturnal-feeding mice.

And when the researchers gave altered mice two of the key ingredients in , the animals didn't get fat.

That's a lot to digest, but it has potential implications for humans as we enter the season of stuffed refrigerators that beckon some to eat when they should be resting.

"One message from our paper is, 'Don't raid the larder at night,' " said Garret FitzGerald, director of the Institute for Translational Medicine and Therapeutics at Penn's Perelman School of Medicine. Lead author Georgios Paschos is a research associate in the lab.

The in mice immediately reminded FitzGerald of human night-eating syndrome, a condition associated with obesity that was first described in 1955 by Penn obesity expert Albert Stunkard. About 1.5 percent of the population has it. FitzGerald's group is now working with the Penn center that treats night eaters, the Center for Weight and Eating Disorders, to set up a study of whether people with the condition share metabolic or with the day-eating mice.

Previous research also has shown that night-shift workers and people with are more likely to be obese.

Even so, Gary D. Foster, director of Temple University's Center for Obesity Research and Education, doubts the mice results can be extrapolated to treatment. What he found intriguing was the power of fat cells to change the animals' metabolism.

"I think this confirms what people have talked about for the past few decades: that fat is metabolically active," Foster said. "It's not just an inert storage tissue. If you can get mice to gain weight consuming the same number of calories, that turns conventional wisdom upside down."

FitzGerald's new line of research, published this month in Nature Medicine, is just a taste of how thoroughly animal bodies are attuned to the daily rotation of the Earth, even at the cellular level.

This circadian regulation has long interested doctors, who noticed that certain conditions such as asthma, depression, heart attacks, and stroke varied with the time of day, FitzGerald said. Our bodies metabolize medicines differently at different times as well.

That may be partly because environmental factors change during the day, but scientists also learned decades ago that our brains house a "master clock." Then they learned that some genes functioned differently at different times of the day and that tissues of all types contained their own little clocks. Those peripheral clocks were thought to be "slave oscillators" that did as the master clock commanded.

FitzGerald's group, which is "interested in the role of these peripheral clocks in cardiovascular function and metabolism," decided to see what would happen if they knocked out the clock gene in mouse fat cells.

The mice shifted 20 percent of their consumption into what should have been their rest period, and they became obese.

The study also provided evidence that the peripheral clock was more powerful than previously thought. When it was knocked out in the , the genes that normally would tell you when to eat and when not to eat became disordered.

A few other genes that govern how unsaturated fatty acids involved in food intake - EPA and DHA - are released in the blood were also disrupted. Levels of EPA and DHA, key ingredients in fish oil, were low during daytime feeding.

With supplementary EPA and DHA, the scientists were able to prevent the weight gain.

FitzGerald sidestepped the two most obvious questions: Should obese people start taking fish oil, and at what time of night should people stop eating?

He did say, though, that he thought our circadian clocks were key "because we need a period of quiescence to recharge our metabolic batteries. ... I think we're meant to rest at night and not be eating."

For scientists, he said, it's important to start with the most serious problem - those who get up to eat - and then see whether lessons from them are applicable to broader groups.

Kelly Allison, an assistant professor at Penn's Center for Weight and Eating Disorders, said she was intrigued by the first animal model of night eating. In humans, someone is said to have night-eating syndrome if he eats at least 25 percent of his food after dinner or wakes up at least twice a week to eat.

She's used to the question about when to stop eating and also didn't answer it. "I don't ever pick a time out of the hat, like after-8 eating is evil," she said. Still, she said, animal studies have been suggesting that we don't make as efficient use of energy consumed at night.

Isn't it time to do a study that will answer the questions?

"We are on it," she said. "We're thinking about how we can do it."

Explore further: It's not just what you eat, but when you eat it

Related Stories

It's not just what you eat, but when you eat it

November 11, 2012
Fat cells store excess energy and signal these levels to the brain. In a new study this week in Nature Medicine, Georgios Paschos PhD, a research associate in the lab of Garret FitzGerald, MD, FRS director of the Institute ...

Green tea helps mice keep off extra pounds

October 4, 2011
Green tea may slow down weight gain and serve as another tool in the fight against obesity, according to Penn State food scientists.

Recommended for you

New vaccine production could improve flu shot accuracy

July 24, 2017
A new way of producing the seasonal flu vaccine could speed up the process and provide better protection against infection.

Molecular hitchhiker on human protein signals tumors to self-destruct

July 24, 2017
Powerful molecules can hitch rides on a plentiful human protein and signal tumors to self-destruct, a team of Vanderbilt University engineers found.

Researchers develop new method to generate human antibodies

July 24, 2017
An international team of scientists has developed a method to rapidly produce specific human antibodies in the laboratory. The technique, which will be described in a paper to be published July 24 in The Journal of Experimental ...

A sodium surprise: Engineers find unexpected result during cardiac research

July 20, 2017
Irregular heartbeat—or arrhythmia—can have sudden and often fatal consequences. A biomedical engineering team at Washington University in St. Louis examining molecular behavior in cardiac tissue recently made a surprising ...

Want to win at sports? Take a cue from these mighty mice

July 20, 2017
As student athletes hit training fields this summer to gain the competitive edge, a new study shows how the experiences of a tiny mouse can put them on the path to winning.

'Smart' robot technology could give stroke rehab a boost

July 19, 2017
Scientists say they have developed a "smart" robotic harness that might make it easier for people to learn to walk again after a stroke or spinal cord injury.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.