Fasting and Growth Hormone

By Jason Fung, MD

  • Growth hormone decreases with age
  • Growth hormone maintains lean mass including muscles and bones
  • Injecting artificial growth hormone causes side effects like high blood sugars and enlarged hearts
  • Fasting naturally boosts growth hormone
  • Fasting increases autophagy (breakdown of protein) while stimulating growth resulting in rejuvenation of tissues
By Jason Fung, M.D., Co-founder of The Fasting Method

Growth Hormone


Human growth hormone (GH) is a hormone made by the pituitary gland (the master gland) and plays a huge role in the normal growth and development of children and adolescents as the name implies. Normal levels of GH peak in puberty and gradually decrease thereafter. Adult GH deficiency leads to more body fat, lower lean body mass and decreased bone mass (osteopenia).

Growth hormone is typically secreted during sleep and is one of the so-called ‘counter-regulatory’ hormones.  HGH along with cortisol and adrenaline tell the body to increase the availability of glucose – so it counters the effect of insulin. HGH only lasts a few minutes in the bloodstream.  It goes to the liver for metabolism, where it is converted into a number of other growth factors, the most important of which is Insulin Like Growth Factor 1 (IGF1).

Scientists first harvested HGH from cadavers in the 1950s (eeewww), but only synthesized it in labs in the early 1980s.  Since HGH typically goes down with age, it became a popular performance enhancing drug for its ‘anti-aging’ effects. Perhaps this decrease in HGH-IGF1 may contribute to the decrease in lean body mass both in lower muscle mass, but also lowered bone mass. So, what are the effects of giving HGH in older people?  This was studied in 1990 in a New England Journal of Medicine article.

Growth Hormone Supplementation

HGH is difficult to measure since it is pulsatile, so IGF1 can be measured as a surrogate. Healthy men with low IGF1 levels were given HGH for 6 months and the effects measured.

Group 1 got HGH supplements group and Group 2 (the control group) did not.  Over 6 months weight overall did not change between the two groups. But that’s not the whole story.

Looking more closely at the lean body mass.  Compared to the control, the HGH group packed on 3.7 kg (8.8%) more lean mass.  That’s 8 pounds of lean mass!  The reason overall weight did not change was because the fat mass decreased by 2.4 kg (5.3 pounds)! That’s a decrease of 14.2%. Even the skin thickness improved.

  • More lean mass,
  • Less fat
  • Thicker skin
  • Thicker bones (not shown)

That’s anti-aging, baby!

Studies in women, such as this randomized, double blinded placebo controlled 2002 JAMA article showed similar results with a decrease in fat mass and an increase in lean mass.  Sounds pretty great.  So, why aren’t we using it for everybody?  Well, there’s a little thing called side effects.

  • Increased blood sugar
  • Increased pre-diabetes
  • Increase blood pressure
  • Fluid retention

Blood sugar rises with HGH supplementation, since it is one of the counter-regulatory hormones.  This resulted in a significantly higher rate of pre-diabetes. Over the long term, there is also a theoretical risk of increased prostate cancer and an enlarged heart. So, that’s not very good news.

So artificial injections of HGH are out. What if there is an all-natural method of increasing growth hormone? What about, say, fasting?

Fasting increases Growth Hormone

In 1982, Kerndt et al published a study of a single patient who fasted for 40 days for religious purposes.  There were several notable changes.

  • Blood pressure slightly decreased.
  • Glucose goes down (from 96 to 56).
  • Insulin goes way down (from 13.5 to 2.91).
  • Glucagon, one of the counter-regulatory hormones, increased from 139 to 727, as expected.

But our concern here is HGH.  It starts at 0.73 and peaks at 9.86.  That is a 1250% increase in growth hormone. Even with a relatively short 5 day fast, we are talking about a 300% increase.  All this HGH increases without drugs.

What about the potential side effects?  Increased glucose? Nope.  Increased blood pressure? Nope.  Higher risk of cancer? Nope.

Other studies have shown the same increase in growth hormone.  In 1988, Ho KY et al studied fasting and HGH. On the control day, you can see that meals (marked M) very effectively suppress HGH secretion.  This is to be expected.  Like cortisol, HGH increases glucose and thus is suppressed during feeding. Fasting is a great stimulus.

During fasting, there is the spike in the early morning, but there is regular secretion throughout the day as well. Hartman et al also showed a 5-fold increase in HGH in response to a 2 day fast.

So, why does fasting to increase growth hormone not have the same side effects? Fasting reduces blood glucose where HGH increases it. So, you are fasting, the net effect on blood glucose is negligible. But if you are simply taking HGH supplements without fasting, you are at risk of higher blood glucose, and therefore pre-diabetes and perhaps type 2 diabetes.

The same goes for blood pressure. Fasting lowers blood pressure slightly and HGH increases it. So, the overall effect on blood pressure is minimal with fasting, but taking HGH supplements leaves you exposed to the risk of higher blood pressure.

Same goes for cancer risk. Fasting will tend to reduce the growth of cancerous cells (by restricting nutrient availability) where HGH will raise it. Once again, taking HGH supplements exposes you to side effects that naturally raising HGH via fasting does not.

Fasting and Lean Mass

This HGH is crucial in the maintenance of lean mass – both muscle and bone. One of the major concerns about fasting is the loss of lean mass.  This does not occur. In fact, the opposite happens – there is likely an increase in lean mass. Think about this for a second.

Let’s imagine that we are living in Paleolithic times.  During the summer of plenty, we eat lots of food and store some of that as fat on our body.  Now it is winter, and there is nothing to eat.  What do you suppose our body does?  Should we start burning our precious muscle while preserving our stored food (fat)?  Doesn’t that sound pretty idiotic?

It’s as if you store firewood for a wood-burning oven.  You pack lots of firewood away in your storage unit.  In fact, you have so much, it is spilling out all over your house and you don’t even have enough room for all the wood you’ve stored. But when the time comes to start up the oven, you immediately chop up your sofa and throw that into the oven.  Pretty stupid right?  Why would we assume our body is also so stupid?

The logical thing to do is to start burning the stored wood.  In the case of the body, we start to burn the stored food (fat stores) instead of burning precious muscle.

This has enormous implications for athletes. While studies are few, it is possible that the elevated HGH stimulated by fasting will increase muscle mass, an important advantage in elite level athletes.

The recovery from hard workouts would similarly be improved.  The increased adrenaline during fasting will also allow you to perform a more intense workout.  It will make workouts easier and recovery faster.

Rather, fasting has the potential to unleash the anti-aging properties of HGH without any of the problems of excessive HGH (prostate cancer, increased blood sugar, increased blood pressure).  For those interested in athletic performance, the benefits are even greater. So, let’s see.

  • Train harder.
  • Lose Weight.
  • Faster recovery.
  • Decrease insulin and insulin resistance.

Decrease sugars.  All of these benefits are achieved without drugs, supplements or cost.  Yes, like all the best things in life, it’s free.

For more, see The Obesity Code.

Learn more about Pique Fasting Tea.

For fasting education, support and community, go to The Fasting Method.



Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

Share this article with a friend

More articles you might enjoy…