Hunger Hormone And Obesity

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

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

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 a person's development of obesity and its subsequent complications.

The regulation of human body weight is a very complex physiological process. In our body there is a certain balance between energy intake and energy expenditure. In obese people, there is a positive energy balance (a surplus), which results in increased body fat and ongoing weight gain.

Researchers everywhere in the world are trying to understand the relationship between appetite control and food intake. With the discovery of the hunger hormone ghrelin, a new field of research has begun to result in new modalities of medical and surgical options for obesity treatment.

How is the Hunger Hormone Ghrelin Produced? How Does It Work 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 the hypothalamus and the pituitary gland in the brain.

The main action of ghrelin is to increase appetite. The mechanism behind its action is rather complex and involves biochemical pathways responsible for the regulation of multiple other hormones in the body, and 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 the hypothalamus, ghrelin activates the appetite stimulating nerve cells whereas in the pituitary gland, ghrelin promotes the release of growth hormone by increasing calcium levels inside the cells. This results in an increased production and release of growth hormone, which promotes overall growth (including weight gain) by controlling the body's 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 the 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.

The hormone also suppresses the release of other compounds by other neurons which suppress appetite. The net effect is an increase in appetite caused by the 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 the stomach transmits signals through the vagus nerve. The vagus nerve supplies fibers to the stomach and promotes stomach contractions. The vagus nerve arises from the brain, reaches the stomach and provides nerve supply to many other organs.

To study the role of the vagus nerve, experiments in rats were done where the nerve fibers to the 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 the vagus nerve is mainly responsible for transmission of ghrelin induced signals from the stomach to the brain.

Ghrelin also increases acid secretion in the stomach and stimulates stomach contractions. These stomach contractions are felt as hunger pangs, which induce people to eat more.

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 these complex processes, which control hunger and appetite, should help scientists to develop effective methods of preventing and treating obesity in the future.

Regulation of Hunger Hormone Production in the Body

The major factor which controls ghrelin secretion is the food that we eat. When we are fasting, ghrelin levels increase in the blood to stimulate hunger. They only fall back to normal after food is taken.

This was proven in animal studies. The effects of glucose on ghrelin secretion have also been studied. When energy stores in the 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 levels in the blood. So ghrelin secretion occurs in both situations of increased and decreased blood sugar levels.

There is a Clear Relation Between 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 is reduced. This can result in a low metabolic rate or a 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 level of growth hormone and a higher metabolic rate. This study has provided a possible method of treatment for obesity 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 people suffering from 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.

Ongoing 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.

As we learn how hormones impact the development of obesity, we can also learn how to harness their power to treat obesity, thus potentially finally putting an end to the obesity epidemic.