Ghrelin – The Appetite Hormone

Introduction & background

Ghrelin, also known as the appetite or hunger hormone, is the first hormone demonstrated to stimulate food intake or appetite in humans. In simple words, this hormone tells your brain that your body has to be fed and you are feeling hungry. Therefore, Ghrelin carries signals messages between your brain and stomach (digestive system). Ghrelin was first described by Japanese researchers in the journal Nature in December 1999. They chose the name ghrelin because “ghre” is the Proto-Indo-European root of the word “grow,” and ghrelin also stimulates the pituitary gland to release growth hormone. Today, scientists consider ghrelin as a potentially important regulator of the complex systems controlling food intake and body weight.


Where is ghrelin produced?

Ghrelin is produced and secreted by specialized cells in the stomach (and to some extent by intestine and placenta) and the upper part of the small intestine.


How ghrelin acts to cause appetite?

Ghrelin is first natural appetite stimulant found to be made outside the brain and its blood concentrations increase progressively before meals and decrease after meals. After its release from stomach and other parts of the body, ghrelin acts directly on the brain. Like leptin, it acts on the hypothalamus (part of the brain). However, unlike leptin, it increases appetite rather than decreasing it.
The levels of ghrelin appear to be regulated throughout the day and are closely correlated with meal time. For example, levels of ghrelin are highest in your blood just before a meal.

What does ghrelin do?

Increases your food intake: As explained above, ghrelin is the hormone that your body makes in order to ensure that you eat enough and lets the body know if the stomach is empty (stimulates appetite). In various studies, Ghrelin has been found to increase the appetite before eating and to decrease it afterward.

More compelling evidence for ghrelin’s role in stimulating hunger in humans is that after injecting ghrelin into the blood and allowing people to consume as much as they please from a buffet, a 30% increase in food intake was found to occur.

It is now established that ghrelin is a peripheral signal from the stomach that is secreted upon hunger. Ghrelin travels in the blood to the brain where it activates neurons in the hypothalamus and stimulates eating. Satiety signals will then feedback to the stomach through vagal afferents (nerves) and decrease the urge to eat.

Helps release growth hormone: Ghrelin is a naturally produced peptide (protein) that releases growth hormone in the body by stimulating pituitary gland in the brain.
Role in weight gain or loss: It has been observed that dieters who lose weight and then try to keep it off make more ghrelin than they did before dieting, as if their bodies are fighting to regain the lost fat, researchers are reporting today in the New England Journal of Medicine.

By contrast, the same study showed that very obese people who have an operation called gastric bypass to lose weight wind up with relatively little ghrelin, which may help explain why their appetites decrease markedly after the surgery. It is said that obese people are sensitive to the appetite-stimulating effects of ghrelin and inhibition of circulating ghrelin may be a useful therapeutic target in the treatment of obesity.

One of the reasons that some people find dieting so difficult to maintain is that when dieting the body will produce ghrelin in response to hunger, thus stimulating eating and fat retention. Anti-obesity drugs usually act by being agonists (stimulate) or antagonists (inhibit) of receptors involved in appetite. Therefore when the drug is taken continuously, weight is reduced but upon stopping the weight may well go back on.

Effect on body fat: Research has demonstrates that ghrelin suppresses the utilization of fat in the adipose tissue. According to international journal of obesity, Ghrelin also favors the accumulation of lipids in visceral fatty tissue, located in the abdominal zone and considered to be the most harmful. Researchers theorize that it causes the over-expression of the fatty genes that take part in the retention of lipids. It is precisely this accumulated fat in the region of the abdomen that is deemed to be most harmful, as it is accompanied by complications, visceral obesity being related to higher blood pressure or type 2 diabetes. Moreover, being located in the abdominal zone and in direct contact with the liver, this type of fatty tissue favors the formation of liver fat (fatty liver).



All in all, based on the above facts and discussion, it can be concluded that ghrelin (the hunger hormone) has a direct role in causing and regulating your appetite. In fact, both leptin and ghrelin act as “non-identical” twins in reducing or increasing your appetite and, hence, have a direct connection with how diet can cause weight gain or weight loss. Fortunately, there are some natural and recommended appetite suppressants in the market that can actually suppress the excessive appetite caused due to the over secretion of ghrelin. The following comparison chart lists some of the highly recommended and quality appetite suppressants.

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