Ghrelin is produced by ghrelin cells which are found in the stomach, lungs, pancreas and kidneys. It is a hormone that regulates hunger. When the stomach is empty, ghrelin is released. When food is eaten ghrelin secretion stops. Ghrelin increases appetite, increases food intake and promotes fat storage.
Ghrelin also promotes the release of growth hormone from the pituitary gland which breaks down fat tissue and helps building muscle tissue.
When people go on ‘yo yo’ diets – extreme calorie cutting diets, the weight they lose during dieting comes back on quick when the diet stops. One of the reasons why this happens is because the ghrelin levels are dramatically increased. The hormone levels stay like that for some time after the diet has stopped. The body reacts as if it went through starvation – which effectively it did, and to protect itself from future starvation it produces more ghrelin. In layman terms: you go on an extremely low calorie diet to lose weight. Your ghrelin levels increase so you feel more and more hungry. You are effectively starving on the diet to lose weight, and when you finally stop the diet, the body – to protect itself from further starvation – produces more ghrelin. Because you stopped the diet you go back eating normal and because you feel hungry you eat more and more – hence you put more weight back than what you’ve lost.
Ghrelin levels are primarily regulated by food intake. Levels of ghrelin increase when fasting (with increased hunger) and are lower in people with higher bodyweight than in lean people.
The different nutrients effect differently the release of ghrelin: protein and carbs slow down the production of ghrelin to a greater extent than fats – eating protein and carbs will make you feel fuller.