Fasting, Bodybuilding, Testosterone and Human Growth Hormone

There is a time for everything under the sun.


  • a time to weep and a time to laugh,
  • a time to mourn and a time to dance
  • a time to bulk and a time to cut
  • a time to carb load and a time to intermittent fast

And so it is, that while I recommend taking supplements for building muscle, I also recommend intermittent fasting — where you go through a cycle of not consuming anything while still building muscle. Contradiction? No! And I’ll explain why this the case below.

Question: Can you build muscle while on a fast?

Answer: yes! This brings us to the subject of this post, or rather 4 subjects: fasting, bodybuilding, testosterone and human growth hormone. Did you know that fasting for 24 hours can boost your body’s production of HGH by a whopping 2000%? Yes, you read that correctly, if you skip meals for a day, you’re swimming in HGH.

This recent study also confirmed earlier findings about the effects of fasting on human growth hormone (HGH), a metabolic protein. HGH works to protect lean muscle and metabolic balance, a response triggered and accelerated by fasting. During the 24-hour fasting periods, HGH increased an average of 1,300 percent in women, and nearly 2,000 percent in men.

So what is HGH? While it provides many benefits to your body, those of most interest to a bodybuilder are found in its ability to promote the synthesis of new protein tissues, such as those necessary for muscle recovery or repair. This is how new muscle tissue is built. And you have 2000% more of it 24 hours after a fast.

Now, there are no studies showing that testosterone is boosted during a fast. However, according to the The Journal of Strength and Conditioning Research publication: “HORMONAL RESPONSES TO CONCURRENT STRENGTH AND ENDURANCE TRAINING WITH DIFFERENT EXERCISE ORDERS”, a regimen of aerobic exercise followed by strenuous weight lifting was followed by a 41.4% boost in testosterone.

There is one sure-fire method to have your body loaded with testosterone and human growth hormone, both at the same time: exercise while fasting.

Insulin Sensitivity

When food is always available to us, the amount of nutrients we absorb from food is diminished. This is an issue with insulin sensitivity. Our bodies produce insulin to absorb nutrients, which becomes more ignored as food is extremely available. However, when food isn’t as available (as during a fast), sensitivity to insulin is increased, and the body then can do more with less. The goal for the body builder is to be highly sensitive to insulin when it comes time to absorb nutrients, such as protein supplements.

Studies have shown that a 20 hour fast improves insulin sensitivity in men.

So then, after a 24 hour fast, your body has increased human growth hormone. It has increased insulin sensitivity. A workout, after a 24 hour fast, and followed up with supplements or a healthy meal provides an optimized scenario for building and repairing muscle. After your workout, right when you need it most, you have testosterone, HGH and an improved ability to absorb nutrients.

What about prolonged fasting?

I believe in the benefits of prolonged fasting, especially for those who are overweight or attempting to regenerate their immune system. However, I do not believe in the benefits of building muscle while engaged in a prolonged fast. The liver has a store of glycogen, and this store is depleted after around 28 hours. This, however, doesn’t take into effect what your last meal was. If you had a huge steak and veggies, a steady stream of amino acids will be released from that meal for another 16 to 24 hours (if it was a 100 grams of protein in the meal), delaying how long it is before your body starts relying on its glycogen store and ultimately extending this time-frame far beyond 28 hours.

Therefore, if engaging in a 24ish fast, and if you had a good protein supplement or similar healthy meal, your body is still ready to respond exceedingly well to a vigorous exercise regimen, and following that up with a protein-rich meal only solidifies your position.

Prolonged fasting (3 days to even a month) can be beneficial for your body. However, this is a completely different beast. After a day of fasting, your glycogen reserves are nearly used up. Your body then begins a conversion into using body fat for sustenance. After 3 days of fasting, your brain receives 30% of its energy from your fat reserves. After 4 days, it receives 75% of its energy from the same. At this time, your brain is functioning on only 30 grams of glucose per day. Of that 30 grams, 20 can be produced by the liver from glycerol. This leaves you with a deficit of 10 grams of glucose per day, that your brain needs to operate. Catabolism (the breaking down of proteins to supply your brain with glucose) then follows. A prolonged fast, though beneficial in many ways, will leave your muscles slowly wasting away in order to provide your brain it’s deficit of glucose.

In summary, intermittent fasting for 24 hours has the ability to help with your bodybuilding effort, and provides other benefits (helps you get that cut look with shrink-wrapped abs). Prolonged fasting isn’t a good idea for bodybuilding purposes, though may come in handy for other scenarios (at the expense of some of your muscle tissue). I suggest you research longer fasts and consult a physician if you are contemplating a fast longer than 24 hours.

Huge Jacked-man

jackman2This is how Hugh Jackman got into shape for his Wolverine character, that you can read about here.

“I do it in a healthier way now,” said the strapping 6-foot-2 Jackman, who lost 15 pounds, then regained 30 pounds for Les Misérables. “I do it with intermittent fasting, so there’s periods where I’m not eating and periods when I eat a lot.”
“There is a lot of science behind intermittent fasting or having a period of each day when you are not eating. So you eat for an eight-hour window and then don’t eat for 16 hours.”

In order to get into shape, his diet consisted of 6000 calories eaten within an 8 hour time-frame complimented with vigorous crossfit workouts, followed by 16 hours of fasting.

Posted in Low Carb Diet