is a gastric hormone, which influences food intake.
- Ghrelin levels may induce appetite through the
vagus nerve throughout the blood-brain barrier to the central nervous
- Exposure to good food
images will lead to increased
hunger and food consumption.
Have you not felt hungry or a
desire to eat after
seeing a picture of a tasty dish? You can now blame a hormone for that! Researchers have come up with a scientific evidence to support
a well-known fact that
appetite can be triggered simply by the sight of tasty food! Sometimes,
you also tend to eat an increased portion size even when you're satiated! Such
habits of overeating
might lead to obesity
The occurrence of obesity has been increasing at an alarming rate and a
significant decrease in longevity
and quality of life
has been represented by this epidemic throughout the world. Therefore, we need to understand the mechanisms underlying obesity and increase in the portion size of food to find potential treatments.
‘Viewing images of tasty food could induce ghrelin - a hormone that triggers hedonic hunger and results in overeating.’
Recent research investigations underlying obesity and the
food intake has recently faced a major shift in focus, from the hypothalamus to
neural circuits that control emotion, cognition and motivational behavior.
Among the above, changes in motivated behavior towards food have emerged as a
new promising treatment target.
In addition to this, the impact of peripheral hormones
that signal nutrition status to the mesolimbic areas, particularly, "Ghrelin"
(the only known circulating orexigenic hormone) has come into focus.
It is the gastric hormone peptide renowned to influence feeding. It is
the major signal for food intake in various species including human beings. It
was identified as an endogenous ligand of the Growth Hormone (GH) secretagogue receptor. The hormone
has been isolated from the stomach as well as the hypothalamus regions. Ghrelin
not only plays an important role in energy balance, but also stimulates the
release of GH, adrenocorticotropic hormone (ACTH) and cortisol in human
beings. In humans, ghrelin stimulates appetite and calorie intake
. Ghrelin levels are found to be elevated before meals and decreased after food intake.
A single intravenous bolus of the hormone given to an individual stimulates hunger
and influences to have a large meal. Ghrelin administration increases calorie intake, appetite and also prompts the imagination of a favourite or tasty food.
Ghrelin acts as a prominent factor in the regulation of appetite in
human beings. The failure of this mechanism in eating disorders
and its connection to addictive behavior demands a deeper understanding of the endogenous processes related to the hormone.
Leptin and Insulin:
There is a reciprocal
interaction that exists in the energy balance between ghrelin & leptin and ghrelin & insulin. While leptin is secreted by the adipose tissue, its receptors are found
in the arcuate nucleus located inside the hypothalamus region where ghrelin is also engaged. Leptin decreases food consumption and
increases energy expenditure. Ghrelin inhibits secretion of insulin and ghrelin secretion is decreased
Ghrelin Stimulates Appetite:
In a study conducted by the department of psychiatry and psychotherapy, Technische Universität Dresden, Germany, the processing of pictures showing food were investigated after overnight fasting using functional MRI and correlated it with blood plasma levels of ghrelin.
The volunteers were made to view images of food and their appetites
were rated. It was found that fasting levels of Ghrelin correlated positively
with food cue reactivity and was
noted that high fasting Ghrelin levels were associated with subjective appetite
during the task.
The study concluded that brain activation and subjective appetite
ratings indicate that ghrelin
elevates the hedonic effects of food pictures. Fasting
levels of ghrelin may
generally cause craving when they are exposed to food cues.
In another study conducted by the department of psychiatry, Max Planck Institute of Psychiatry, Munich, ghrelin was isolated from the stomach and hypothalamus of rats and human beings. It was investigated if the injection of the hormone affected
human eating behavior. They injected 100 mg ghrelin in young control subjects and found that the appetite was
enhanced. More so, it stimulated an increase in plasma levels of GH instantly. The results
revealed that Ghrelin stimulated appetite and images of food.
Ghrelin Levels Increase After Seeing Pictures
While Ghrelin administration seemed to increase appetite
, calorie intake and picturization of favorite food, it was unclear as to whether the hormone's levels would be affected by external cues like the sight of food.
Environmental factors like the visual exposure to food have been claimed
to influence eating habits in human beings. The sight of hedonic food enhances
the desire to eat even when they feel full or satiated. There was no clarity as
to which physiological mechanism triggers the motivation for food intake
independent of the metabolic energy status. It was thus essential to test the
hypothesis that ghrelin
levels increase in healthy volunteers after visual presentation of images of
The Effect of Visual Presentation of Images of Food on Ghrelin Plasma
Levels in Healthy Subjects:
A study conducted by Max Planck Institute of psychiatry, Germany has investigated the influence
of images of food on ghrelin
levels in young subjects. Their study lasted two consecutive sessions with a
During each session, blood samples were
collected and then plasma concentration of ghrelin were analyzed.
Plasma total ghrelin
was measured using commercial radio-immunoassays.
During the first session, they showed 50 non-food images and during
the next session, images of food were showed on a computer screen. The images
of food demonstrated savory and sweet meals which were typical for a German
lunch like pizza, steak, ice cream, chocolate cake and Viennese schnitzel
pizza. The non-food
images comprised of various sceneries and objects that did not involve any context of eating
behavior such as clouded sky, piano, bicycle, pair of shoes.
The images were presented to the subjects in a randomized order for a
total duration of 15 minutes. Each picture was shown thrice averagely for six
seconds. The experiment was carried out in a quiet room and the subjects were
seated in a comfortable armchair. They were video monitored to not fall asleep.
Visual representation of food resulted in a significant increase of ghrelin. As expected, ghrelin levels increased before each meal
independent of the contents of the pictures. In addition to that, it was found
that ghrelin levels increased significantly over the
30-minute interval following the exposure to images of food, compared to that
of the interval following the exposure to non-food images. There was a significant difference in
the increases between the exposures to the two different picture conditions.
It was concluded that the sight of food images elevates ghrelin levels in healthy
subjects. The increase in ghrelin
was related to the visual stimulus and wasn't induced by an internal cue like a
conditioned time schedule for food consumption or pre-existing feeling of
hunger. They were shown five pictures and asked to recognize if they had seen the picture before.
But they did not find any significant correlation between the results of the
recognition test and that of the increase in ghrelin hormone. They were also asked to rate the taste of food
images which also did not seem to correlate with plasma ghrelin
There is now strong evidence that ghrelin produced majorly in the stomach region induces its
orexigenic effects through
the vagus nerve and the brainstem to the hypothalamus. The elevated ghrelin levels may induce
appetite through the vagus nerve throughout the blood-brain barrier to the
central nervous system. The study
confirms that the strongest ever orexigenic hormone, ghrelin was induced by perception of
images with food.
This finding supports the hypothesis that external factors contribute
to eating behaviour in modern society where the visual representation of food
products is very common. This study has revealed that exposure to images of
food will lead to exceeded food consumption and Hedonic hunger (Eating driven
by pleasure, instead of the need for calories).
In the future, it is likely that
nutritionists and dietitians
will start advising people to refrain from viewing images of food to prevent hedonic hunger and
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increase after pictures showing food.
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appetite, imagination of food,
GH, ACTH, and cortisol, but does not affect leptin in normal controls. Neuropsychopharmacology. 2005
- Kroemer NB1, Krebs L, Kobiella A, Grimm O, Pilhatsch M, Bidlingmaier M, Zimmermann US, Smolka MN. Fasting levels of ghrelin covary
with the brain response to food pictures. Addict Biol. 2013 Sep:855-62. doi: 10.1111/j.1369-1600.2012.00489.x.
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