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The discovery of hunger hormone ghrelin provided a new insight into the mechanism of appetite and weight regulation. This new area of research might hold a clue to successful treatment of obesity.

Worldwide, obesity and related metabolic disorders like diabetes, heart disease, hypertension and sleep apnea are increasing. In some industrialized countries, the problem of obesity has reached almost epidemic proportions.This also leads to the rise in the treatment-related costs, with millions of dollars being spent to address these lifestyle-associated problems.

Scientific research revealed that the problem is rather complex, and there is no single simple way of addressing it. Body weight control involves many physiological mechanisms. 

There is no single approach which would help to each and every affected individual.

Regulation of appetite is a new target in the obesity research

In recent years it is becoming clear that the so-called hunger hormone, ghrelin, which increases appetite plays an important role in developing the obesity and its complications.

Regulation of body weight is a very complex process. In our body there is a certain balance between energy intake and energy expenditure. In obese people, there is a positive energy balance which results in increased body fat and weight gain. Researchers everywhere are trying to understand the relation between appetite control and food intake. With the discovery of ghrelin a new field of research has begun resulting in newer modalities of medical and surgical options for obesity treatment.

Hunger hormone production and action in the body

The hunger hormone ghrelin is produced mainly in the stomach, though smaller amounts are also produced in pancreas, small intestine and colon. The concentration of ghrelin decreases from duodenum to colon. A very small amount of ghrelin is also secreted by hypothalamus and pituitary in brain.

The main action of ghrelin is to increase appetite. The mechanism behind its action is rather complex and involves biochemical pathways responsible for regulation of multiple other hormones in the body, growth hormone in particular. Ghrelin binds to the growth hormone secretion-promoting receptors in the hypothalamus and pituitary in brain. In the arcuate nucleus of hypothalamus, ghrelin activates the appetite stimulating nerve cells whereas in pituitary gland, ghrelin promotes the release of growth hormone by increasing calcium levels inside the cells. This results in increased production and release of growth hormone which promotes overall growth by controlling the body metabolism.

The hypothalamus area of brain strongly controls the eating habits and appetite of people. The ghrelin containing nerve cells are found in two areas of hypothalamus - the arcuate nucleus and paraventricular nucleus. The former is the primary site of ghrelin action. In the arcuate nucleus, ghrelin stimulates the release of certain compounds responsible for increasing the appetite. It also suppresses the release of other compounds by other neurons which suppress appetite. The net effect is an increase in appetite caused by hunger hormone. In the paraventricular nucleus, ghrelin stimulates corticotrophin releasing hormone-related neurons which in turn release adrenocorticotrophic hormone (ACTH) and cortisol. This results in an increase in blood sugar levels.

Studies have also shown that ghrelin in stomach transmits signals through vagus nerve. Vagus nerve supplies fibers to the stomach and promotes stomach contractions. Vagus nerve arises from the brain, reaches stomach and provides nerve supply to many other organs. To study the role of vagus nerve, the experiments in rats were done where the nerve fibers to stomach were blocked. Ghrelin in these rats failed to induce appetite, growth hormone secretion and activation of appetite-causing compounds in nerve cells. This experimental study showed that vagus nerve is mainly responsible for transmission of ghrelin induced signals from stomach to brain.

Ghrelin also increases acid secretion in stomach and stimulates stomach contractions. These stomach contractions are felt as hunger pangs.

Complex Biochemistry Of Hunger Hormone Holds The Key To Obesity Treatment

The mechanisms outlined above do sound complex. Indeed, their complexity is one of the reasons they were discovered only recently. But their understanding allows scientists to have a clear view of the processes taking place in our body. Even more importantly, understanding of these processes should help to develop effective methods of preventing and treating obesity.

Regulation of hunger hormone production in the body

The major factor which controls ghrelin secretion is food that we eat. During fasting, ghrelin levels increase in blood. They fall back to normal after food is taken.

This return to normal levels is faster when diet contains proteins or sugar and is considerably slower if fatty food is consumed.

This was proven in animal studies. The effects of glucose on ghrelin secretion have also been studied. When energy stores in body are low, ghrelin stimulates glucose production and storage.

Studies have shown that ghrelin stimulates gastrin and insulin secretion. Both of these compounds are secreted in response to the increased glucose level in blood. So ghrelin secretion occurs in both situations of increased and decreased blood sugar levels.

There is a clear relation between the hunger hormone production and obesity

Ghrelin has become the main target of research in the treatment and prevention of obesity. Ghrelin plays a major role in the growth hormone secretion and regulation of appetite.

Studies have also shown that in the obese individuals, the level of growth hormone reduces resulting in low metabolic rate or lesser burning of calories. Clinical evidence shows an inverse relation between body weight and levels of both ghrelin and growth hormone. Administration of ghrelin in these obese individuals resulted in an increased levels of growth hormone and metabolic rate. This study has provided a possible method of treatment by altering growth hormone levels in obese individuals.

Ghrelin secretion responds differently to different types of food intake in obese people. Recent findings indicate that the hormone responsible for signalling satiety called ‘peptide YY’ rises less in obese in comparison to normal weight individuals. It was suggested that the hunger and satiety signals do not function normally in obesity.

Type II diabetes is seen commonly in patients with morbid obesity. They have insulin resistance, insulin deficiency and increased blood sugar levels. A study has shown lower levels of ghrelin in these individuals which may be the reason for development of type II diabetes.

On-going research has shown that ghrelin may be only one of the hormones responsible for controlling appetite and food consumption. More research is needed to understand the complex interactions involved in food intake and energy expenditure signals in the body. The biochemical mechanisms here are complex, but their full understanding will be valuable for developing the new medical approaches for treating obesity.

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