Ghrelin
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Ghrelin is a peptide hormone that plays a key role in the regulation of appetite, energy homeostasis, and body weight. It is often called “the hunger hormone,” because its concentration rises before a meal and stimulates the feeling of hunger. Ghrelin affects not only food intake, but also metabolism, energy storage, growth hormone secretion, and the functioning of the gastrointestinal tract. This hormone constitutes an important element of the gut-brain axis, i.e., the communication system between the digestive system and the central nervous system. In recent years, ghrelin has become the subject of intensive research concerning obesity, eating disorders, pharmacological treatment of overweight, and metabolic changes associated with rapid weight loss.
Ghrelin - what is it
Ghrelin is a peptide hormone composed of 28 amino acids, first isolated in 1999. It is the only known peripheral hormone that directly stimulates appetite. It acts by activating GHS-R (growth hormone secretagogue receptor) receptors, located mainly in the brain's hypothalamus, which is the structure responsible for controlling hunger and satiety.
The hormone occurs in two basic forms:
- active ghrelin (acylated) – biologically active, appetite-stimulating,
- inactive ghrelin (deacylated) – exhibits different metabolic and regulatory functions.
Ghrelin participates in numerous physiological processes:
- regulation of appetite,
- control of growth hormone secretion,
- modulation of glucose metabolism,
- influence on gastric motility,
- control of the body's energy balance.
Its action is the opposite of leptin, a satiety hormone produced by adipose tissue. In practice, the body maintains a balance between hunger and satiety signals precisely through the interaction of ghrelin, leptin, insulin, and other gut hormones.
Ghrelin - where is it produced
The largest amount of ghrelin is produced in the gastric mucosa, mainly within the fundus of the stomach. It is estimated that about 70–80% of the total hormone production comes from this very location. Smaller amounts are also synthesized in:
- the small intestine,
- the pancreas,
- the hypothalamus,
- the pituitary gland,
- the lungs,
- the kidneys,
- the placenta.
The production of ghrelin depends on the body's nutritional status. Its concentration:
- increases during fasting,
- decreases after consuming a meal,
- increases with restrictive diets,
- may remain chronically elevated in individuals after significant weight loss.
The circadian rhythm is also of significant importance. The highest levels of the hormone are observed immediately before scheduled meal times. The body sort of “learns” the regularity of eating meals, which is why ghrelin also participates in the mechanisms of appetite conditioning.
Studies have shown that ghrelin secretion is influenced by:
- sleep duration,
- stress,
- physical activity,
- glucose and insulin levels,
- diet composition,
- the rate of body fat loss.
Ghrelin - how it works
Ghrelin acts primarily by affecting the hypothalamus, where it activates neurons secreting neuropeptide Y (NPY) and AgRP protein. These are among the most potent central appetite stimulants.
The mechanism of action of the hormone includes several key effects:
Ghrelin action | Biological effect |
|---|---|
Appetite stimulation | increased appetite |
Slowing down energy burning | saving calories |
Effect on the stomach | increased motility and emptying |
Growth hormone stimulation | anabolic effect |
Regulation of glucose metabolism | effect on insulin sensitivity |
Ghrelin also affects the reward system in the brain. It increases the activity of structures responsible for the pleasure of eating, especially high-energy foods. For this reason, a chronic increase in the concentration of the hormone can make appetite control difficult and promote overeating.
An interesting phenomenon is the increase in ghrelin levels after intensive weight loss. The body interprets weight loss as an energy threat and activates defense mechanisms aimed at restoring the previous weight. This is why long-term maintenance of the effects of weight reduction is a biologically difficult process.
Ghrelin and the feeling of hunger - mechanism
Ghrelin is one of the most important biological signals initiating hunger. Its concentration begins to rise even before the stomach becomes empty, which indicates that the hormone participates in both metabolic and behavioral regulation.
The mechanism behind the feeling of hunger is multi-stage:
- The stomach remains empty for a longer period of time.
- Cells of the mucous membrane increase the secretion of ghrelin.
- The hormone enters the bloodstream.
- Ghrelin reaches the hypothalamus.
- Appetite-stimulating neurons are activated.
- The feeling of hunger and the motivation to eat appear.
After consuming a meal, the level of ghrelin begins to drop. It is particularly strongly lowered by:
- protein,
- fiber,
- high-volume meals,
- glycemic stabilization.
On the other hand, a highly processed diet, sleep deprivation, and chronic stress can disrupt the proper regulation of the hormone. As a result, the body may generate more frequent hunger pangs despite an adequate energy supply.
The importance of ghrelin is also observed in patients using GLP-1 analogs, such as semaglutide. These drugs indirectly affect the reduction of appetite and the modulation of hunger signals, leading to reduced calorie intake and body weight reduction.
Ghrelin and body weight - the relationship
The relationship between ghrelin and body weight is complex and multidirectional. Counterintuitively, people with obesity often have lower baseline ghrelin levels than lean individuals. This is because the body adapts to chronic energy excess. However, the problem remains an impaired hormonal response after a meal and excessive reactivity of reward centers.
The increase in ghrelin after weight loss is of particular importance. After losing weight, the body:
- increases the feeling of hunger,
- decreases energy expenditure,
- intensifies the tendency to regain weight.
This is one of the main mechanisms responsible for the yo-yo effect. The faster and more restrictive the weight reduction, the stronger the compensatory hormonal response can be.
A large loss of fat tissue can also affect the appearance of the face and body. In aesthetic medicine, phenomena related to the following are observed:
- loss of facial volume,
- skin laxity,
- atrophy of fat pads,
- increased gravitational aging,
- deepening of expression lines.
In such cases, procedures supporting skin quality and tissue reconstruction are used, including:
- tissue biostimulators,
- microneedle radiofrequency treatments,
- HIFU,
- collagen therapies,
- regenerative procedures improving skin tension,
- treatments rebuilding facial volume.
