Ghrelin is an important hormone that plays a vital role in hunger and satiety. There are several diseases that have been linked to fluctuating levels of ghrelin and some of these include:

• Obesity – Among obese and overweight individuals, the blood ghrelin levels are lower compared to among those with a normal body weight. Ghrelin levels increase before meals and decrease after meals, a mechanism has its roots in the hypothalamus. If the lateral hypothalamus is removed (as seen in animal studies), feeding becomes less frequent leading to severe weight loss and death. If the ventromedial hypothalamus is removed, feeding increases leading to weight gain and severe obesity.
• In people with Prader-Willi syndrome, however, increased ghrelin levels seem to contribute to obesity. In individuals that are obese as a result of this condition, fasting levels of ghrelin are markedly raised.
• Among people suffering from eating disorders such as anorexia nervosa, the plasma levels of ghrelin are higher than in individuals who are thin or even normal-weight. The ghrelin concentration is also increased in bulimia nervosa patients.
• Ghrelin also plays a role in sleep, with more hours of sleep achieved the lower the ghrelin level.
• The ghrelin level is also raised in cancer-induced cachexia or weight loss that is associated with cancer.
• In individuals who have undergone bariatric procedures such as a gastric bypass surgery, the capacity of the gut is markedly reduced and so is the ghrelin level compared to normal weight controls and individuals who lose weight using diet changes alone.
• The ghrelin concentration is also decreased in patients with short bowel syndrome.
• Some studies have also noted a role of ghrelin in the onset of Parkinson’s disease.
• The ghrelin concentration is reduced in people who are treated with somatostatin and its analogs, such as octreotide.