To maintain body weight, there must be an energy balance: energy intake has to be equal to energy expenditure. Two hormones that seem to play a role in the regulation food intake and body weight are leptin and ghrelin. Leptin and ghrelin systems are disturbed in obesity. Ghrelin is the hunger hormone and leptin is the stop appetite hormone. Many believe the actions of these “go and stop” appetite hormones are straightforward, and that one is good and the other is bad.
Ghrelin was originally isolated from the stomach but it also has been found in the gastrointestinal tract, pancreas, ovary, and the adrenal cortex. The secretion of ghrelin depends on the nutritional state. Ghrelin stimulates the brain, which leads to an increase in appetite, and it slows metabolism, and decreases the body’s ability to burn fat. Throughout the course of the day, ghrelin levels change dramatically. Ghrelin levels are increased before meals and decreased after meals. Ghrelin levels are influenced by gender, BMI, glucose and insulin levels. Leptin also has an effect on circulating for ghrelin levels.
Normally ghrelin levels go up dramatically before eating; this signals hunger. They go down for about 3 hours after eating. A diet high in protein suppresses ghrelin more effectively than a diet high in fat and carbohydrates. When the stomach is empty ghrelin is secreted. When the stomach is full and stretching secretion stops. Sleep deprivation was associated with an increase in ghrelin levels, appetite, and hunger.
Leptin is released into the circulatory system by adipose tissue (fat cells). It signals the brain information about energy stores. Leptin helps signal the brain that the body has enough energy including body fat stores. Leptin sends messages to parts of our bodies to tell us we’ve had enough. When we eat fatty meals this system doesn’t work as well.
The development of leptin resistance mostly involves a period of overeating, resulting in the leptin system getting so disturbed that it leads to sustained defects. Overeating results in an increase in circulating leptin levels.This exposure of the hypothalamus to high leptin levels causes an altered leptin sensitivity.
You’d expect the body to increase ghrelin if a person is under eating and decrease if he or she was over eating. In obese subjects, the circulating levels of leptin is increased, whereby surprisingly, the levels of ghrelin is decreased. It is now established that obese patients are leptin resistant. It is unknown if the abnormality of the leptin and ghrelin levels are the cause of a consequence of obesity
If ghrelin stimulates hunger, wouldn’t a ghrelin inhibitor be effective in helping people lose weight. Several pharmaceutical companies are conducting research on such a medication. There could possibly be a ghrelin blocking medication.
Gastric bypass creates a small gastric pouch and bypasses the duodenum. Gastric bypass patients exhibit different plasma ghrelin profiles. They lack the pre meal increases in plasma ghrelin that is seen in normal individuals is much lower. Ghrelin levels are also reduced following sleeve gastrectomy.
What is not known is how important the role of ghrelin in everyday eating and weight gain/loss. More research is needed as our body has a complex system of hormones that interact in countless ways.