Why Do HGH Secretions Increase When Fasting?

Woman's feet on weight scale

Human growth hormone, or somatotropin, increases when you fast. Under normal circumstances, HGH promotes the synthesis of lean muscle and the storage of glycogen as well as fat. However, when you fast, increased levels of the hormone stimulate the breakdown of fatty tissue, according to Niels Moller of Aarhus University Hospital in Denmark. Your body needs the fat to produce energy,

How it Works

The increase in HGH during fasting helps to preserve your muscle tissue and glycogen stores while using your fat stores instead. This breakdown of fat, which is called lipolysis, releases free fatty acids and glycerol, which are then metabolized to produce energy. According to Madelon Buijs, researcher at Leiden University Medical Center in the Netherlands, levels of HGH, which is produced by the pituitary gland, rise noticeably within 13 hours after starting a fast.

Blood Levels

In cases of a lack of HGH during fasting, protein loss from muscle increases by about 50 percent. In addition to fasting, exercise and stress can also increase HGH levels. They are also subject to much variation during the day, because your pituitary gland releases the hormone in bursts. Random measurement of HGH, as opposed to monitoring it over a period, is not very useful. Moreover, levels in the morning will be higher, according to LabTestsOnline.org.


In nonfasting individuals, insulin regulates glucose metabolism for energy, but during periods of fasting, HGH becomes predominant. However, lipolysis may be blunted in obese individuals during periods of fasting due to different factors, one of which may be their lower levels of HGH. This effect may cause obese individuals to retain adipose tissue. However, the lower HGH may also protect them against the effects of excessively high levels of free fatty acids, which can be toxic to cells.

Additional Information

HGH testing is not routine. It is usually performed to help diagnose pituitary problems, which can lead to conditions such as stunted growth or gigantism. Although HGH therapy is approved for treating stunted growth in children, HGH has also attracted more general attention because of its effects on muscle and fat tissue. Synthetic HGH is available for purchase, although not much is known about its long-term safety. Consult your physician if you have questions.