We all recognise appetite as the urge to eat, but what drives this urge? Hormones, gut peptides and neural signals all have a part to play in regulating our appetite – and one of the key hormones in this process is ghrelin.
What is ghrelin?
Ghrelin was discovered in 1999 by Masayasu Kojima, Kenji Kangawa and their colleagues at a laboratory in Japan. Described as a ‘hunger hormone’ ghrelin is released when the stomach is empty, circulates in the bloodstream and sends a message to the hypothalamus directing us to consume food.
Levels of ghrelin decrease after a meal then gradually increase over time, eventually causing hunger pangs and encouraging us to eat again.
Ghrelin also stimulates the release of growth hormone in the pituitary gland.
What affects ghrelin levels?
People who are overweight tend to have lower levels of ghrelin than those who are thin. Additionally, overweight people will find that their ghrelin levels only fall slightly after they eat, as the hypothalamus isn’t sent a strong enough signal to stop consuming food. This sustains appetite and makes it difficult for overweight people to lose weight or maintain weight loss.
How does ghrelin relate to satiation and satiety?
Satiation is the series of processes that tell us to stop eating and satiety is when the drive to eat is supressed for some time after we have eaten.
The release of ghrelin is part of the process of satiation and satiety, encouraging us to have the right intake of nutrients for health. Even a small imbalance, such as the addition of one sugary snack or drink a day, can cause us to gain weight over a period of time.
This is because when energy consumed is more than energy expended, weight gain occurs, leading to potential health issues such as Type 2 diabetes, heart disease, stroke and certain cancers.
Do mealtimes affect ghrelin?
Research has found that ghrelin can adapt to our regular mealtimes. If you eat breakfast at 8am and eat your next meal at 12 noon, your ghrelin levels will rise just before the expected meal. However, if you usually wait until 1pm to eat again, your ghrelin rates will adjust and increase an hour later. This pattern is the same whether you are thin or overweight.
Food as a reward
Another issue relating to ghrelin is the type of food we choose to eat. Consuming foods that are high in energy but low in nutrients – for example, meals and snacks high in fat, sugar, salt and artificial additives – will stimulate the brain and positively reinforce our urge to eat these foods. This leads to a vicious cycle, where the body craves particular kinds of food.
How can we improve ghrelin function?
There are two key ways to improve ghrelin function. The first is to avoid food and drink high in sugar, as these can negatively impact ghrelin levels after consumption.
The second is to ensure every meal contains a good level of protein. This will reduce ghrelin levels and help to ensure satiety.
How does the body allow us to feel satiated?
One of the most recognised ways to feel satiated is the release of the hormone leptin. This will be the subject of a future blog.