Growth Hormone + IGF-1: How Fasting + Eating Control Fat and Muscle

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Why Being Hungry And Then Eating Might Be The Whole Fat Loss And Muscle Building System

Growth hormone is released when you're hungry. That is the observation I keep coming back to with clients, and once you sit with it for a second, the rest of the system starts making sense.

Before zooming in, walk the whole chain. You go without food, your body has to find fuel from somewhere, so it reaches for stored body fat. Then you eat, fuel is suddenly available, and the body switches jobs from finding energy to using energy. Two different phases, two different priorities, and the same hormone sitting at the center of both.

This is the signal that's telling your body to burn fat. Growth hormone pushes fat cells to release stored fat into the bloodstream so it can be broken down and burned, and there is real work behind that mechanism. In growth hormone transgenic carp, researchers found liver fat catabolism was measurably increased through enhanced lipolytic and fatty acid beta-oxidation pathways, which is a technical way of saying the growth hormone signal turned up the machinery that takes fat apart for fuel (Wu et al., 2022).

Fish are not people, and I want to be straight about that. But the pathway is old and conserved, and it lines up with what we see in humans doing training in a fasted or low-fuel state.

Now the second half. Well, what happens when you eat? Well, when you eat, that triggers your body to convert that growth hormone at the liver into IGF-1.

I want to flag something here, because I care more about you understanding this than me sounding certain. I have never seen a study that lands cleanly on hunger intensity scaling growth hormone output, or on eating being the trigger that converts growth hormone into IGF-1 at the liver. That is the model I use, and it is how I explain it to the guys I coach, but the literature has not answered it the way I would want.

What the research has established is what IGF-1 does once it shows up. IGF-1 is the part of this mechanism that helps your body build and repair muscle and tissue. In a 2020 study on skeletal muscle repair, a signaling protein called Meteorin-like drove muscle regeneration specifically through a Stat3/IGF-1 mechanism, meaning IGF-1 was the messenger doing the actual repair work downstream (Baht et al., 2020).

So put both halves together. When I'm hungry, my body releases growth hormone, tells it to convert fat into a source of fuel because I don't have energy on hand.

And then food arrives, and the body no longer needs to go hunting for energy. So it's converted at the liver to IGF-1 so that we can leverage the resources that we just consumed to help our body repair.

Boom, that's how growth hormone works.

The practical version is simple, and you do not need a supplement or a protocol you have to schedule your life around. Spend a stretch of your day genuinely hungry, train during or near that window, and then eat a real meal with protein afterward. Hunger phase for fat, fed phase for repair.

There is a useful detail on the training side. When trained women performed resistance exercise, fat oxidation stayed elevated for hours afterward and the metabolic effect extended well past the session itself, so the window you create with lifting is longer than the lifting (Allman et al., 2019).

If you are lean already, or you are chasing a hard strength number, do not white-knuckle the hungry phase. Push the fed side harder and let the hunger phase be shorter, because you will not build much on a body that never gets resources.

Most people treat hunger as a failure of willpower and eating as a reward. The body treats them as two halves of the same instruction, and it needs both to finish the sentence.

If you want the full training and nutrition system built around this, come join us in the Iron Forge Brotherhood: https://www.skool.com/jh-iron-forge-brotherhood/about

Research: Wu et al., 2022, Front Endocrinol; Baht et al., 2020, Nat Metab; Allman et al., 2019, J Appl Physiol.

References:

Allman BR, Morrissey MC, Kim JS et al.. Fat metabolism and acute resistance exercise in trained women. J Appl Physiol (1985). 2019. https://pubmed.ncbi.nlm.nih.gov/30605402/

Wu Y, Li R, Wu X et al.. Improved liver lipid catabolism and utilization in growth hormone transgenic common carp (Cyprinus carpio L.) through enhanced lipolytic and fatty acid β-oxidation pathways. Front Endocrinol (Lausanne). 2022. https://pubmed.ncbi.nlm.nih.gov/36171901/

Baht GS, Bareja A, Lee DE et al.. Meteorin-like facilitates skeletal muscle repair through a Stat3/IGF-1 mechanism. Nat Metab. 2020. https://pubmed.ncbi.nlm.nih.gov/32694780/