Introduction:
Hunger hormones are the hormones responsible for stimulating and inhibiting hunger. Ghrelin is responsible for inducing the feeling of hunger, and leptin is responsible for inducing a feeling of fullness after eating. Ghrelin plays an important role in regulating glucose and energy homeostasis. The levels of ghrelin increase before eating and while fasting, and it reduces after eating and remains low up to three hours after eating. An imbalance in the level of ghrelin and leptin can lead to eating disorders and severe obesity.
What Are Hormones?
Hormones can be defined as a group of molecules in multicellular organisms transported to distant cells and organs through complex biological processes to regulate physiology and behavior in the body. These hormones are chemical messengers in the body that are transported by the bloodstream to various body parts, deciphering messages and acting accordingly. Hormones work by inducing responses in organs or tissues developed to respond to them. Hormones affect the body's growth, development, metabolism, sexual function, and mood over many years. Multiple disorders can be caused when the endocrine glands underproduce or overproduce these hormones.
What Are Hunger Hormones?
Hunger hormone or ghrelin is a hormone produced by the specialized cells of the gastrointestinal tract. These specialized cells producing the hormone are known as enteroendocrine cells; these cells are responsible for producing peptides to respond to various stimuli and release them into the blood. Ghrelin is called the hunger hormone because it increases the drive to eat; it instructs the brain when it is time to eat. Ghrelin also prepares the body for food intake by increasing the movement of the gastrointestinal tract and stimulating the release of gastric acids. Therefore, ghrelin plays an important role in the regulation of appetite as well as digestion. The blood ghrelin levels are highest before eating and exponentially fall after eating. Apart from ghrelin, other hormones, like leptin, cortisol, pancreatic polypeptide, female sex hormones, etc., affect and regulate hunger.
What Are the Functions of Ghrelin?
The functions of ghrelin are as follows:
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Energy Homeostasis: The primary function of ghrelin is the regulation of energy homeostasis, which can be defined as the process involving coordinated homeostatic regulation of energy inflow (through food intake) and energy outflow (through energy expenditure).
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Regulation of Body Weight: As a result of energy homeostasis, ghrelin ultimately affects and regulates body weight. Since ghrelin is responsible for sending hunger signals to the brain, it can readily increase body weight and body mass.
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Reward-Seeking Behavior: Ghrelin activates the cholinergic-dopaminergic reward link, which uses neurotransmitters to evaluate rewards and motivate the brain to obtain them. These natural rewards are usually food or addictive drugs.
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Release of Growth Hormone: Ghrelin is also responsible for stimulating the release of growth hormone from the pituitary gland.
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Sleep Cycle: Ghrelin plays a crucial role in regulating the sleep and wake cycle. Sleep restriction has been reported to affect the release of ghrelin.
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Taste Sensation: Ghrelin plays an important role in the perception of taste.
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Reproduction: Ghrelin is known to have an inhibitory effect on gonadotropin-releasing hormone, which may eventually cause infertility.
How Does Ghrelin Work?
Ghrelin’s mode of action involves activating cells of the anterior pituitary gland and activating an aggregation of neurons found in the mediobasal region of the hypothalamus (known as the hypothalamic arcuate nucleus). These neurons include the neuropeptide Y neuron, which is responsible for appetite or hunger.
How Is Ghrelin Controlled?
Ghrelin levels are regulated by food consumption. The level of ghrelin is noted to be highest just before eating a meal and while fasting. Therefore, eating eventually reduces the levels of ghrelin in the blood. Certain foods control the release of ghrelin a lot more than other foods. For example, carbohydrates and proteins control the production and release of ghrelin more than fats. Some of the digestive hormones, like somatostatin, also inhibit the release of ghrelin.
What Happens if There Is Excess Ghrelin?
Excess ghrelin in the body can cause severe obesity, uncontrolled hunger, inability to sense satiety after eating, and learning disabilities. In addition, ghrelin levels increase in conditions like cachexia, anorexia nervosa, Prader-Willi syndrome, etc.
What Happens if There Is a Lack of Ghrelin?
Lack of ghrelin in the body will lead to complete loss of appetite and weight loss. Extreme loss of ghrelin occurs after a person undergoes gastric bypass surgery. Gastric bypass surgery is done in case of severe obesity in which the size of the stomach is reduced, lowering the ghrelin levels.
What Is Leptin?
Leptin is primarily produced by adipose tissues (fat cells) and enterocytes. Leptin is responsible for inhibiting or controlling hunger and reducing fat storage in the body. However, in obese individuals, there is a reduced sensitivity to leptin which causes uncontrolled hunger pangs and increased appetite because the body fails to detect satiety (feeling of fullness after eating). This eventually leads to excess weight gain.
Why Is Ghrelin-Leptin Harmony Necessary?
Maintaining a balance between ghrelin and leptin levels in the body is crucial. Both the hormones associated with hunger must function harmoniously to maintain a healthy diet. Ghrelin should increase the appetite, and leptin should detect satiety after eating a meal; If there is an imbalance between this equation, the ability to eat the right amount of food or the ability to stop eating when full will be unsettled. A correct balance between ghrelin and leptin levels will help maintain healthy body weight. In addition, an imbalance in this harmony will lead to anorexia or obesity.
What Are the Other Functions of Ghrelin?
Recent studies have shown that ghrelin is not just a hunger hormone; its functions are vast and complicated. The functions of ghrelin go way beyond its orexigenic functions. Other functions of ghrelin include:
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Cardiac Functions: Ghrelin is present in cardiac cells and responsible for generating contractile forces in the heart muscles.
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Muscle Atrophy: Ghrelin can indirectly increase muscle mass by increasing food intake and growth hormone secretion.
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Cancer: Ghrelin has been detected in various endocrine and nonendocrine tumors. Studies have reported that ghrelin exhibits proliferative properties in cancer.
What Are the Other Hormones That Affect Hunger?
Other hormones that may affect hunger are :
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Cortisol: Also known as the stress hormone, it is released in times of distress and when the body is under stress. This may lead to an increase in appetite in some individuals.
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Pancreatic Polypeptide: This is a digestive enzyme secreted by the pancreas and plays a role in hunger reduction.
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Female Sex Hormones: Testosterone and progesterone are known to increase hunger, while estrogen inhibits hunger.
Conclusion:
Hunger hormones, ghrelin, and leptin are extremely important for maintaining a healthy body weight in an individual. These hormones must function in harmony in inducing and controlling hunger to maintain an energy balance in the body. Maintaining a normal level of ghrelin is essential. It can be done by eating a healthy diet, exercising regularly, eating more protein, checking stress, and getting enough sleep.
