Need an excuse for overeating at Christmas?
December 29th 2009 21:26
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Blame it on your hunger hormone
By David Derbyshire Mail on Line
No matter how much you've eaten, or how full you are feeling, the prospect of an extra slice of cake or wafer-thin mint can sometimes be too tempting.
Now scientists have discovered why some people crave sugary, fatty food - even when they are completely stuffed.
A study has shown that the so-called hunger hormone ghrelin - which the body produces when it is feeling peckish - encourages the brain to seek out high calorie food, no matter how much we have eaten.
Full up? A study has show that the hunger hormone ghrelin encourages the brain to seek out high calorie food, no matter how much we have eaten
The finding helps explain why Christmas lunch all too often turns into an orgy of overeating and why people still find room for an after dinner chocolate when they are fit to burst.
Scientists and supermarkets have long known that hunger makes food look more appealing, and that people who shop on an empty stomach usually bring home more food than they were planning to buy.
Past studies have shown that ghrelin - a hormone produced in the stomach - acts on the brain to make certain foods more attractive.
Now a experiment at the University of Texas Southwestern Medical Center suggests that ghrelin might also work on the brain to make people crave fatty foods when they are already full.
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Dr Jeffrey Zigman, a co-author of the study, said: 'What we show is that there may be situations where we are driven to seek out and eat very rewarding foods, even if we're full, for no other reason than our brain tells us to.'
The researchers tested the role of the hormone on laboratory mice given a large meal.
Once the creatures were fully sated, they tested whether they preferred a room where they had previously found high-fat food over one that had only offered regular, bland snacks.
Dr Zigman and colleagues found that when mice were injected with an extra dose of the hunger hormone ghrelin, they strongly preferred the room that was associated in their brains with the high-fat diet.
Mice without the extra dose of hormone showed no preference, the scientists report in the journal Biological Psychiatry.
In a second experiment, the team watched how long mice would continue to poke their noses into a hole in order to get a pellet of high-fat food.
'The animals that didn't receive ghrelin gave up much sooner than the ones that did receive ghrelin,' Dr. Zigman said.
Ghrelin has been shown to intensify the pleasurable feelings that animals get from cocaine or alcohol. The scientists believe that it also increases the 'high' from eating calorific food.
Dr. Mario Perello, the lead author of the mouse study, said the idea was to find out 'why someone who is stuffed from lunch still eats - and wants to eat - that high-calorie dessert.'
'We think the ghrelin prompted the mice to pursue the high-fat chow because they remembered how much they enjoyed it,' he said. 'It didn't matter that the room was now empty; they still associated it with something pleasurable.'
The researchers also found that using drugs to block the action of ghrelin stopped the mice from spending as much time in the room they associated with the high-fat food.
Humans and mice share the same type of brain-cell connections and hormones - and have similar 'pleasure centres' in the brain, the scientists say. That suggests that the hormone plays a similar role in people.
Ghrelin is produced by cells in the stomach. As well as making fatty food look attractive, helps the brain learn and may play a role in fighting off depression. The hormone was discovered 10 years ago.
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