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Restricted meal times might not be the best idea for dieters, study suggests

Limit what you eat, not when you eat.

PETER DOCKRILL
31 DEC 2015
 

If you're thinking of trying to lose a little weight, you might be considering a diet that limits the amount of calories you'll consume during the day. But regardless of the food plan you choose, it might not be the best idea to restrict your eating to limited windows during the day.

A new study has found that rats learn to eat more when their feeding schedules become restricted, thanks to a hunger hormone that kicks in to help them make the most of their limited chow-time.

 

The hormone in question is called ghrelin, the effect of which reduces the feeling of fullness when we consume food. In the study, the rats had their meal times restricted to a daily 4-hour window over the course of several days. After the hours had passed, a full 20 hours would follow before the rats had a chance to feed again.

This restrictive feeding schedule boosted the ghrelin hormone in the rats, encouraging them day-by-day to eat more, until they eventually learned to double their usual food intake. The findings are reported in eLIFE.

"We are looking deep into the higher order functions of the brain to unpick not just which hormones are important for controlling our impulses but exactly how the signals and connections work," said Scott Kanoski, one of the researchers from the University of Southern California.

The researchers found that ghrelin communicates with neurons in the hippocampus – a region of the brain that controls memory and motivation, and is likely related to how anticipation of food can increase intake.

Once ghrelin has stimulated feelings of appetite in the hippocampus, the neurons there then tell the hypothalamus to produce a molecule called orexin, which promotes excessive eating – also known as polyphagia or hyperphagia.

If the whole process turns out to work in humans the same way, it might just help us to control eating habits that contribute to health problems like obesity. According to the researchers, the ghrelin hormone may once have been an important survival mechanism, but it's well past its use-by date in the developed world.

"This is an adaptive response to limited food access, but one that is no longer relevant in the Western world," said Kanoski, "where instead we need to find new ways to help us fight some of the feeding responses we have to external cues and circadian patterns."

The researchers previously found that ghrelin signals to the hippocampus could increase rats' food intake in response to visual signals the animals had learned to associate with an imminent meal – much like Pavlov's dog.

If they can figure out how to reduce the effect of ghrelin by genetically suppressing the activity of a receptor in the hippocampus that responds to the hormone, we might be able to turn off the switch that encourages us to binge on large quantities of food. And for many in developed countries, that can only be a good thing.

"Over a third of Americans are obese and another third are overweight," said Kanoski, "so we feel we have an obligation to help identify new ways to reduce the burden on society and on our healthcare systems."

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