Pay up and eat up: The true cost of food

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  • Published: Aug 1, 2011
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Pay up and eat up: The true cost of food

Hormonally yours

Ghrelin, a naturally occurring gut hormone, increases our willingness to pay for food, while simultaneously decreasing our willingness to pay for non-food items, according to researchers who have tracked behaviour linked to the hormone with functional MRI. The study supports the modern adage: don't shop for food when you're hungry.

Speaking at the 2011 annual meeting of the Society for the Study of Ingestive Behavior (SSIB), researchers explain how the activity of the gut hormone ghrelin might explain some of our behaviour regarding paying for food, especially why we are apparently willing to pay more for food when we are hungry than when we are not.

Ghrelin is a peptide that exists in two general forms. The first is an inactive pure peptide form, the second active form is octanoylated. The hormone is made primarily by the P/D1 cells that line the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered to be the counterpart of the hormone leptin, which is produced by adipose tissue, which induces satiation when present at higher levels. Ghrelin seems to be closely related to calorie intake, especially given that ghrelin levels in the blood plasma of "normally" obese people are lower than those in leaner individuals. People with the eating disorder anorexia nervosa have higher plasma levels of ghrelin than normal.


Ghrelin reward

Apparently, one way in which ghrelin acts is by increasing activity in brain "reward" region, the ventromedial prefrontal cortex, when people view pictures of food. In this latest study, researchers Deborah Tang of Montreal Neurological Institute and Department of Psychology, at McGill University, in Montreal, Canada, together with J.E. Han, Alain Dagher of Montreal Neurological Institute, also at McGill and neuroeconomist Antonio Rangel of the California Institute of Technology, in Pasadena, USA, were interested to discovery whether or not ghrelin affects a person's willingness to pay for food and non-food items. They examined brain activity using functional magnetic resonance imaging (fMRI) in 29 normal weight volunteers while they placed bids for food or for non-food trinkets after being injected with ghrelin, or after being injected only with saline as a control.

The team found that treatment with the hormone ghrelin increased significantly the volunteers' willingness to pay for food items. However, it reduced their willingness to pay for non-food "trinkets". The researchers say that, as expected, activity within several brain reward regions was correlated with bid values on both food and non-food items in the saline-ingesting control group. Those volunteers treated with ghrelin displayed activity correlated with the brain reward region, the nucleus accumbens.

"Neurally, we found greater activity in the VMPFC after previous ghrelin administration when brain response to food was modelled as a function of bid value," the team explains. "Conversely, the VMPFC bid effect for trinkets was greater in the saline condition. Results suggest that previous ghrelin increases the motivational value of foods by increasing the value assigned to food stimuli in the VMPFC."

The team asserts that their results support the view that ghrelin increases hunger and eating, in part, by increasing reward signalling specifically in the nucleus accumbens. The hope is that a clearer understanding of brain-reward signalling mechanisms may lead to better ways to control appetite and so fight overweight and obesity problems.

 



The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 Ghrelin, a naturally occurring gut hormone, increases our willingness to pay for food, while simultaneously decreasing our willingness to pay for non-food items, according to researchers who have tracked behaviour linked to the hormone with functional MRI. The study supports the modern adage: don't shop for food when you're hungry.

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