How does your body control your appetite? Have you ever wondered why your stomach growls when you are hungry and why you stop eating when you feel full? Or why fasting and overeating may be related? Many substances help control our appetite, but two hormones in particular are recognized to have a major influence on regulating this process. They are ghrelin and leptin.
The role of ghrelin and leptin in the regulation of food intake and body weight in humans is complex and not yet completely understood. They can also be influenced by age and gender.
Ghrelin is called the “hunger hormone” because it stimulates appetite, increases food intake, and promotes fat storage. It is a gut-brain peptide thought to operate between the stomach and the brain via the vagus nerve, one of the largest nerves in the body.
Circulating ghrelin concentration rises before meals and falls after meals. Total ghrelin level increases during the night and decreases after breakfast. Ghrelin levels increase after dieting, which may explain why diet-induced weight loss can be difficult to maintain. Ghrelin levels are primarily regulated by food intake but other factors found to be important in the regulation of ghrelin production include nutrients, hormones, and the autonomic nervous system.
Ghrelin is synthesized in the hypothalamus but is also found in the gastric mucosa, pituitary gland, hippocampus, brain cortex, adrenal gland, intestine, pancreas, and many other human tissues. The complex biochemical pathways of this hormone and its influence on appetite suggest further studies are necessary.
Compared with leaner individuals, ghrelin is lower in individuals with a higher body weight, which suggests that ghrelin could be involved in the long-term regulation of body weight. It is also known that carbohydrates and proteins restrict the production and release of ghrelin to a greater extent than fats do. (1,2)
Leptin is the balancing partner of ghrelin as it decreases appetite and increases fat burning thus suppressing food intake and stimulating weight loss. After eating a meal your stomach distends and the secretion of ghrelin decreases. At the same time leptin, the “satiety hormone” increases giving you a sensation of fullness as a signal is sent to your brain to stop eating.
Leptin is mainly synthesized and secreted by adipose (fat storage) tissue. It would seem that obese individuals would have an inherent mechanism to stop eating since leptin concentration in obese individuals is significantly higher than normal. However, the interactions of leptin are also influenced by sensitivity to insulin and insulin levels resulting in a complex system of weight regulation in both obese and normal people. There may also be other physiological factors involved in those who are overweight. (3)
There are other hormones that influence ghrelin besides leptin. Several research studies done mainly on laboratory rats and mice have provided the following information which may be useful in the future treatment of various disorders.
Insulin is produced in the pancreas and helps in the metabolism of glucose. Studies have shown that it may inhibit ghrelin secretion. This may explain the low ghrelin levels found in patients with type II diabetes mellitus. Glucose also inhibits ghrelin secretion which may explain why eating sweets can kill your appetite.
The influence of insulin and glucose on ghrelin secretion is probably contradictory and independent. Also, it is worth noting that insulin sensitivity, rather than insulin itself, may play a more important role in the regulation of ghrelin. (4)
Glucagon is another peptide hormone also produced by the pancreas. It counteracts the actions of insulin by stimulating the liver to release stored glucose thereby increasing blood glucose levels. This increase in glucose suppresses ghrelin secretion and thus your appetite.
Glucagon may also increase growth hormone and glucocorticoids which then inhibit ghrelin secretion. Mixed research results suggest more studies need to be done. (5)
Administration of human growth hormone in cultured rat gastric tissue inhibited total ghrelin secretion. Conversely, ghrelin secretion was stimulated either directly or indirectly through the reduction of growth hormone. This may have future implications for HGH therapies in both children and adults. (6)
Estrogen is mainly produced in the ovaries. Mixed results on the effect of estrogen on ghrelin during estrogen therapies showed slight increases and decreases of ghrelin levels. This may cause overeating and weight gain often seen with estrogen replacement therapy. Other discoveries suggest that eating food high in estrogen, fatty acids, or triglycerides affects ghrelin secretion and may explain the weight gain effect, especially from high-fat diets. (7)
Overeating & Weight Regulation
Back to the opening question: does the hunger hormone cause overeating… the answer? Possibly. You can now see how complex the relationship can be between the numerous substances that regulate our sensations of hunger. Disruptions, both physiological and pathological, in any one of the regulatory substances can influence eating patterns and so much more.
As an example, a laboratory study from Lund University in Sweden demonstrated that diets rich in fat and/or sugar (sucrose) caused overeating in mice. A surprising finding was that sugar, particularly in liquid form, was a powerful inducer of overeating and that dietary fat was less powerful. In view of the increased body weight and fat tissue in the mice, neither elevated leptin nor suppressed ghrelin was able to control/restrain their overeating. Other factors at play may include visual attractiveness and flavor of the food. In humans, this might be translated into cravings, desire for specialty foods, and possibly the state of health of the person. (8)
What You Can Do To Regulate Your Hunger Hormones
- Get proper sleep
- Manage stress
- Exercise consistently
- Eat a regular whole foods diet (9)
Ghrelin and the other hormones associated with appetite have a vast range of physiological functions which influence eating patterns and weight management. Current knowledge of these hormones, particularly ghrelin and leptin, is far from satisfactory. Further studies still need to be done to understand their complexity and biological roles in the body.
- Higgins SC, Gueorguiev M, Korbonits M. Ghrelin, the peripheral hunger hormone, Ann Med, 2007, vol. 39 (pg. 116-136)