Free Scientific Article Explains Why the Sight of Food Makes Us Hungry

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Have you ever noticed how that just by flipping through a magazine filled with images of food and recipes, or watching a cooking show on TV can get your stomach growling and put you in mood for an immediate snack—even though you may have eaten a full meal only an hour ago? As it turns out, researchers may have found the reason why this is such a universal reaction. Below is a summary of an experiment that found that increased levels of a major appetite-inducing hormone is present in the blood of test subjects after viewing images of indulgent foods.

Previous studies have shown that external environmental clues such as the sight of a plate of doughnuts or some other “decadent” type of food increases the feelings of hunger within individuals. However, a physiological explanation for this has been lacking and therefore has motivated scientists to discover how and why seeing food can elicit a hunger response even when a person is not really hungry.

For years now, researchers have known that one of the key factors behind feelings of hunger is associated with a neuropeptide hormone called “ghrelin” that is primarily secreted by the stomach and proximal region of the small intestine. Ghrelin has been found to be a major stimulus for food intake in humans and rodents in studies where exogenous ghrelin was given.

When human subjects are given ghrelin, they report an increased sensation of hunger and were found to consume more calories as well as report that they also felt induced to think about their favorite dishes. When rodents are given ghrelin, an increase in number of feedings and gain of weight are observed.

In a recent study available free online that is published by the journal Obesity, researchers wanted to test whether the blood levels of ghrelin can be increased naturally in normal, healthy, non-obese individuals when exposed to images of favorite foods.

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Eight healthy male volunteers of normal weight and without any factors that may interfere with the test results such as mental illness, suffering from anxiety, recent weight loss or gain, involvement in excessive exercise or dietary regimens, etc. were chosen to participate in the food visualization/ghrelin blood level experiments.

To ensure that the volunteers were reasonably similar and objective in their tastes for food, each was measured against a standard the researchers had developed earlier where the response to 50 color photographs of food and 50 images of nonedible objects was measured by a different group of male volunteers who assigned the images as being very tasty (score of 1) to not tasty (score of 7). Food items that rated very tasty for the males included foods like steak, Viennese Schnitzel, ice cream and chocolate cake.

In the experiment, the eight volunteers were subjected to two separate sessions in which blood draws were performed in numerous intervals before and after a short presentation of neutral (non-tasty item) images in the first session and tasty images in the second session. All volunteers ate a standard breakfast and lunch during the testing. Plasma blood levels of the ghrelin hormone, leptin, and insulin were measured from each of the intervals.

What the researchers found was that visual imagery of food resulted in a significant increase of the ghrelin hormone in comparison to the time interval before the test subjects were presented with images of food. Images of non-tasty items had no effect on the blood plasma levels of ghrelin. The measured levels of leptin and insulin were not affected by either imagery sessions.

The researchers concluded that their findings suggest that external, environmental cues such as the sight of indulgent types of food causes an elevation in ghrelin levels in young, healthy subjects of normal weight in spite of not feeling hungry prior to the image exposure. The researchers state that they believe that their,”…finding supports the hypothesis that environmental factors contribute to eating behavior in modern society, where the visual presentation of food products is common.”

Image Source: Courtesy of MorgueFile

Reference: “Ghrelin Levels Increase After Pictures Showing Food” Obesity (2012); Vol. 20 No. 6 , 1212–1217. doi10.1038/oby.2011.385; Petra Schüssler et al.

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