What is Growth Hormone?
Growth hormone (GH) is made by the pituitary gland and is controlled in the bloodstream by various other hormones, many of which are produced in other parts of the brain, the GI and the pancreas. GH levels increase after exercise, after trauma, and even while we sleep. Levels vary throughout the day, so testing GH isn’t very useful because the pattern can be random, except in the evening, when levels are typically elevated.
As its name implies, growth hormone contributes to bone and muscle growth by increasing protein production. In fact, growth hormone deficiency, a rare condition occurring in children, presents as stunted growth and short stature.
Growth hormone opposes the action of insulin to raise blood sugar levels and increase stored fat mobilization. It also increases protein and muscle production. These actions alter body composition. After middle age, GH levels naturally tend to decline, resulting in diminishing muscle mass and hormones, and increased fat storage. Naturally, scientists are interested in learning new ways to boost growth hormone levels as we age to enhance health.
How Fasting Influences GH
One way to encourage GH production may possibly be through fasting. In one study, young men fasted for two days, resulting in a 5x increase in GH levels. At the same time, during a fast (for a few days), the body strives to conserve fuel and muscle.
Among the metabolic effects of GH are increased lipolysis (breaking down fat), conserving protein, higher blood sugar, and body composition changes. Two highly desired effects that can be achieved through purposeful and prolonged fasting are weight loss through enhanced muscle building and fat breakdown. Research indicates that GH both slows protein and muscle breakdown and increases protein synthesis throughout the body, which may result in building more muscle tissue. These actions are highly desirable for seniors, who are predisposed to sarcopenia (muscle wasting) and frailty syndrome.
A study showed that giving GH treatment to malnourished patients on hemodialysis improved their muscle protein synthesis. In other studies where GH was administered, the results demonstrated improved lipid metabolism and lipid oxidation, causing scientists to wonder if this is the key to resolving the obesity epidemic. One study treated middle age men with GH for nine months, and found that the men had reduced fat mass in the abdominal area, reduced blood pressure, and improved metabolism of sugar and lipids. A nine-week study involving obese women showed that GH increased lipid oxidation, and reduced their total fat mass. The results of this study may indicate that fasting helps weight loss in ways far beyond caloric reduction.
Experimenting with different patterns of fasting may hold promise for identifying effective weight loss solutions to address the obesity epidemic.
The metabolic role of growth hormone in humans with particular reference to fasting. Helene Nørrelund, Growth Hormone & IGF Research 15 (2005) 95–122