Ghrelin

Ghrelin

Brief expert definition: What is Ghrelin, how it works in the body, and how it is applied in sports nutrition.

Short answer: Ghrelin, discovered in 1999, is the "hunger hormone" that signals the brain for food, with levels rising before meals and falling afterward. Chronically elevated levels in athletes in energy deficit can lead to constant hunger. Practical tip: To control ghrelin, include sufficient protein (1.6-2.2 g/kg body weight) and fiber, and distribute meals into more frequent, smaller portions.

Ghrelin is a hormone that stimulates appetite by using signals from the gastrointestinal tract to the brain.

For a more in-depth review, see the full nutrition guide — a foundational guide from the Sport Zona expert team.

What is Ghrelin?

Ghrelin is a hormone that signals our brain that we are hungry, making us want to eat.

📖 Ghrelin

Ghrelin is a peptide hormone known as the 'hunger hormone', which is primarily produced in the stomach and stimulates appetite and food intake by signaling to the brain.

Ghrelin is a peptide hormone, discovered in 1999, that affects appetite, energy balance, and our weight. Its primary site of synthesis is the enteroendocrine cells (specifically P/D1 cells) in the stomach lining, but it is also produced in smaller amounts in the intestines, pancreas, kidneys, and hypothalamus. It is the only known circulating hormone that exhibits an orexigenic effect, meaning it stimulates the feeling of hunger.

The hormone exists in two main forms: acylated ghrelin (the active form) and des-acylated ghrelin (the inactive form). Acylation, a process where a lipid moiety is attached to the molecule, is necessary for its biological activity and its ability to bind to receptors. The ratio between these two forms can vary depending on the physiological state.

Known as the "hunger hormone," ghrelin signals the brain of the need to consume food. Its blood levels typically rise before meals and decrease significantly after food intake, making it an important player in the short-term and long-term regulation of energy homeostasis.

What is Ghrelin and How Does it Work?

Ghrelin is a hormone that helps maintain energy balance by stimulating feeding when needed and is involved in modulating the reward system associated with food. It is linked to growth hormone secretion and is an important indicator of energy deficit in the body.

  • Helps maintain energy balance by stimulating feeding when needed
  • Involved in modulating the reward system associated with food
  • Linked to growth hormone secretion
  • An important indicator of energy deficit in the body

Disadvantages

  • Chronically high levels lead to constant hunger
  • Makes it difficult to adhere to weight loss diets
  • Can contribute to fat accumulation in case of imbalance
  • Elevated levels in athletes with energy deficit can worsen recovery

Ghrelin's action occurs by binding to specific ghrelin receptors, known as growth hormone secretagogue receptors (GHSR-1a), which are widely distributed in various areas of the body, including the hypothalamus, pituitary gland, brainstem, pancreas, and adrenal gland. In the hypothalamus, the main center for appetite control, ghrelin activates neurons that produce neuropeptide Y (NPY) and Agouti-related protein (AgRP), which are potent appetite stimulants.

Ghrelin's mechanism of action includes directly stimulating appetite, as well as influencing metabolism and energy expenditure. Ghrelin has been found to:

  • Increase food intake and fat accumulation.
  • Stimulate growth hormone secretion.
  • Influence glucose metabolism and insulin secretion.
  • Affect the functions of the digestive system, including stomach motility.
  • Participate in modulating the brain's reward system associated with food.
In this way, ghrelin coordinates feeding behavior with the body's physiological needs.

Why is Ghrelin Important for Athletes?

Ghrelin is a hormone whose understanding is particularly important for athletes to optimize their nutritional regimen, control weight, and improve recovery. In athletes, especially those in periods of energy deficit, ghrelin levels can be chronically elevated, leading to constant hunger and making it difficult to adhere to a diet.

Studies show that intense training can temporarily suppress ghrelin secretion, but chronic energy deficit leads to an adaptive increase in its levels. For effective hunger management, athletes should aim for a balanced nutritional intake, including sufficient protein (recommendations between 1.6-2.2 g/kg body weight) and fiber, which are proven to aid in satiety and suppress ghrelin. Distributing meals into more frequent, smaller portions can also help stabilize ghrelin levels and prevent hunger spikes. Maintaining adequate sleep and avoiding chronic stress also have a positive impact on hormonal balance, including ghrelin.

What are the Related Concepts?

  • Leptin — An antagonist of ghrelin, which signals satiety and long-term energy status.
  • Energy Balance — Represents the relationship between calories consumed and expended, which ghrelin directly influences by stimulating food intake.
  • Cortisol and Eating — High levels of cortisol (the stress hormone) can affect ghrelin levels, exacerbating hunger and eating behavior.
  • Insulin Sensitivity — Ghrelin can interact with insulin and affect glucose metabolism, which is important for insulin sensitivity.

Leptin is an antagonist of ghrelin that signals satiety and long-term energy status. Energy balance represents the relationship between calories consumed and expended, which ghrelin directly influences by stimulating food intake, and Cortisol and Eating refers to high levels of cortisol (the stress hormone) that can affect ghrelin levels, exacerbating hunger and eating behavior. Insulin sensitivity is a condition where ghrelin can interact with insulin and affect glucose metabolism.

For athletes aiming for weight reduction, I recommend a protein intake of 1.8-2.2 g of protein per kilogram of body weight, distributed evenly throughout the day, to control ghrelin levels and hunger. — Petar Mitkov

Remember: Understanding and managing ghrelin is key to controlling appetite, weight, and optimizing your nutritional regimen, especially for athletes.

Scientific Sources

  1. Ghrelin is an acylated peptide that releases growth hormone from the stomach., 1999
  2. Ghrelin: structure and function., 2005
  3. The role of ghrelin and leptin in the regulation of food intake and body weight in humans: a review., 2007
  4. Review of the role of ghrelin in appetite, food intake, and energy balance in humans and animals., 2005

Expert Note from Sport Zona

From my experience with athletes in Bulgaria, I often observe how stress and insufficient sleep alter hormonal balance, including ghrelin. This leads to increased appetite and difficulties in weight management, even with a strict diet. Regulating these factors is key to success.

Frequently asked questions

What is the hormone Ghrelin and what is its main function?

Ghrelin is a hormone, often called the "hunger hormone," primarily produced in the stomach. It signals the brain about the need for food intake, with its levels rising before meals and falling afterward.

How does Ghrelin work in the body?

Ghrelin acts by binding to specific receptors in the brain, especially in the hypothalamus. This stimulates neurons that increase appetite, and can also affect metabolism, energy expenditure, and growth hormone secretion.

Why is understanding Ghrelin important for athletes?

For athletes, controlling Ghrelin is key to optimizing nutrition and recovery. Chronically elevated levels can make dieting difficult and lead to reduced energy intake, which is particularly important during low body fat percentages or energy deficits.

How can athletes manage Ghrelin levels?

Athletes can manage Ghrelin levels through a balanced intake of protein and fiber, which promote satiety. More frequent meals with smaller portions, good sleep, and stress management also contribute to hormonal balance.