Growth hormone works to prevent weight loss

For many years, the role of growth hormone (GH) has been simply thought to stimulate bone maturity and linear bone growth and maintain tissues and organs throughout life. However, researchers at the University of Sao Paulo (USP) in Brazil have discovered a new role for GH - when the body loses weight, it acts directly on the brain to conserve energy.

GH receptors are abundantly present in muscles and tissues, livers, and organs directly involved in growth metabolism. But the team found that the brain is also full of GH receptors. This is a brand new discovery. They also discovered that brain GH not only participates in growth metabolism but most importantly, it affects the body's metabolic response to energy storage during starvation or dieting. This new scientific discovery is important for understanding why weight loss is so difficult.

For decades, scientists have been trying to understand why it is so difficult to lose weight after a successful diet but why it is so easy to recover weight. Leptin has so far been considered the main hormone that saves energy when we are hungry.

It is known that the level of leptin in the bloodstream decreases with weight loss, but a person who tries to lose weight by dieting or leptin treatment is rarely able to do so.

Obviously, the weight loss process involves several metabolic processes and hormones other than leptin. This is where GH works. The GH receptor in the brain is located in the hypothalamus, the highest center of the autonomic nervous system. The impulse from the hypothalamus affects the cells of the nerve graft system and regulates smooth muscle tissue in the intestines and blood vessels, the heart muscle, all glands and kidneys, and other organs.

The agouti-related protein (AgRP) is one of the most powerful appetite stimulants. To deeply investigate the effects of GH signaling on AgRP neurons, the researchers did a large number of experiments with AgRP-specific GH receptor knockout mice and control wild-type mice. They measured systemic energy expenditure in two groups of mice on a 60 percent food-restricted diet. 

They found that control mice reduced energy expenditure during food restriction, which is consistent with an adaptive response to energy savings in this case. However, the energy consumption of AgRP GHR knockout mice during food restriction was significantly reduced, indicating that they did not save energy as effectively as control mice.

Therefore, AgRP GHR knockout mice have a higher rate of weight loss, mainly due to reduced fat mass (energy reserve) but also reduced lean body mass (important organs, bones, muscles, ligaments, tendons, and body fluids).

In other words, weight loss causes an increase in hypothalamic GH levels, which activates AgRP neurons, which in turn increase the production of AgRP, which increases appetite and reduces energy metabolism and consumption, making weight loss more difficult.

Conservation of energy is very important to living things. As gradual evolution, human has two mechanisms of energy conservation, one activated by leptin and the other activated by GH. This is why leptin-based weight loss treatments work ineffectively. To lose weight, you must consider the GH mechanism at the same time.