Leptin
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Leptin is a peptide hormone playing a key role in the regulation of the body's energy balance, appetite control, and maintaining a stable body weight. It was discovered in 1994 as a product of the ob gene (obesity gene) and since then has been recognized as one of the most important metabolic signals between adipose tissue and the brain. Leptin informs about the amount of energy stored in the form of adipose tissue, influencing the feeling of satiety, metabolic rate, and energy expenditure. The proper functioning of leptin is an essential element of the body's homeostasis. Disorders of its secretion or leptin resistance are associated with obesity, excessive appetite, metabolic disorders, and difficulties in maintaining a proper body weight.
Leptin - what it is
Leptin belongs to the group of adipokines, i.e., hormones secreted by adipose tissue. It is a protein composed of 167 amino acids, whose main task remains transmitting information about the state of the body's energy reserves to the central nervous system. This hormone acts primarily on the hypothalamus, a brain structure responsible for controlling appetite, metabolism, and hormonal balance.
Leptin concentration in the blood remains proportional to the amount of adipose tissue. The greater the mass of adipose tissue, the higher the concentration of leptin. Physiologically, this leads to a reduction in appetite and an increase in energy expenditure. This mechanism is intended to protect the body from excessive energy accumulation.
Leptin also participates in many other biological processes, including:
- regulation of glucose metabolism,
- influence on insulin sensitivity,
- control of reproductive functions,
- immune response,
- regulation of inflammatory processes,
- control of hormonal balance.
In clinical practice, the phenomenon of leptin resistance, i.e., the body's reduced sensitivity to the action of leptin, is of particular importance. This condition often occurs in people with excess body weight and causes increased appetite to persist despite high levels of the hormone.
Leptin - where is it produced
The main site of leptin production is adipocytes, i.e., white adipose tissue cells. The largest amount of the hormone is produced in subcutaneous adipose tissue, although its synthesis also occurs in visceral adipose tissue.
In addition to adipocytes, leptin can also be produced in other tissues and organs, including:
- the placenta,
- the stomach,
- skeletal muscles,
- bone marrow,
- the mammary gland,
- immune system cells.
Leptin production depends on many metabolic and hormonal factors. Its concentration increases under the influence of:
- an increase in the amount of adipose tissue,
- excessive calorie intake,
- insulin action,
- chronic positive energy balance,
- inflammation.
Conversely, a decrease in leptin concentration is observed during:
- starvation,
- restrictive diets,
- intense physical exertion,
- significant loss of adipose tissue,
- malnutrition.
The body treats the drop in leptin as a signal of an energy threat. In response, there is an increase in appetite and a slowing of metabolism, which constitutes an adaptive mechanism protecting against energy loss.
Leptin - how it works
Leptin acts primarily through leptin receptors present in the hypothalamus. Upon binding to the receptor, neuronal pathways affecting the regulation of hunger and satiety are activated.
This hormone acts on two main neuronal systems:
- inhibits orexigenic neurons responsible for stimulating appetite,
- activates anorexigenic neurons responsible for the feeling of satiety.
As a result, leptin:
- reduces appetite,
- limits food intake,
- increases energy expenditure,
- increases thermogenesis,
- affects fat and glucose metabolism.
Leptin interacts with many other appetite-regulating hormones, including:
- ghrelin,
- insulin,
- peptide YY,
- GLP-1,
- cholecystokinin.
Under physiological conditions, this mechanism enables the maintenance of a relatively stable body weight despite variable energy intake.
A significant metabolic issue is leptin resistance. In this state, the brain stops responding properly to high concentrations of leptin. The body interprets the situation as if energy reserves were insufficient, despite the presence of an excessive amount of adipose tissue. This leads to a chronic feeling of hunger, increased appetite, and further weight gain.
Leptin and the feeling of satiety - mechanism
Leptin is one of the primary satiety hormones. Its action is based on transmitting information to the brain about a sufficient amount of energy stored in the body.
After consuming a meal and an increase in energy supply, adipocytes increase leptin secretion. The hormone reaches the hypothalamus, where:
- inhibits hunger centers,
- reduces the need for further food consumption,
- stabilizes the feeling of satiety,
- limits impulsive eating.
Leptin also affects the reward system in the brain. It limits the excessive activation of structures responsible for the pleasure associated with eating, especially high-calorie products rich in sugars and fats.
In clinical practice, however, it is observed that many people with obesity have very high concentrations of leptin, and yet still experience an increased appetite. This phenomenon results from leptin resistance. This mechanism resembles insulin resistance, where despite high hormone levels, a weakened biological response occurs.
Factors contributing to leptin resistance include:
- chronic obesity,
- highly processed diet,
- excess of simple sugars,
- chronic inflammation,
- sleep deprivation,
- chronic stress,
- low physical activity.
Leptin resistance is currently recognized as one of the key mechanisms in the development of metabolic obesity.
Leptin and body weight - the relationship
Leptin remains closely linked to the regulation of body weight and the amount of adipose tissue. Under physiological conditions, an increase in the amount of fat leads to an increase in leptin concentrations, which should limit appetite and stabilize weight.
In practice, this mechanism stops working properly in many people. In obesity, high concentrations of leptin are usually observed with simultaneous leptin resistance. The body does not properly receive the satiety signal, which leads to:
- maintenance of excessive appetite,
- difficulty in reducing body weight,
- slowing of metabolism,
- greater susceptibility to the yo-yo effect.
During intensive weight loss, however, there is a rapid decline in leptin. The body interprets this as a state of energy threat and triggers adaptive mechanisms:
- increased feeling of hunger,
- decreased energy expenditure,
- increased energy conservation,
- greater susceptibility to weight regain.
This phenomenon explains why maintaining the effects of body weight reduction is sometimes more difficult than losing weight itself.
Modern metabolic medicine emphasizes that effective body weight control requires not only calorie restriction, but also improving the body's hormonal sensitivity. Among other things, the following are important:
- regular physical activity,
- adequate amount of sleep,
- a low-processed diet,
- glycemia stabilization,
- reduction of chronic inflammation,
- avoiding extreme caloric restrictions.
In an aesthetic context, rapid loss of adipose tissue associated with impaired leptin regulation can lead to loss of facial volume, skin laxity, and increased symptoms of gravitational aging. In such cases, procedures that improve skin quality and restore lost volume find application, including tissue biostimulation, microneedling radiofrequency, HIFU lifting, treatments using hyaluronic acid, and technologies that stimulate collagen remodeling.
