Dear Mark: Fasting, Training, and Growth Hormone; Wear and Tear on the Arteries

For today’s edition of Dear Mark, I’m answering a couple of questions from the comment sections of the last couple weeks. First, it’s been established that fasting and exercise both raise growth hormone. What about fasted exercise—does that have an even stronger effect? And what about continuing to fast after your fasted workout? Then, I discuss the inevitability (or not) of wear and tear on the arteries from blood flow-induced shear stress. Is shear stress “bad,” or do certain factors make it worse?

Let’s dig in.

Marge asked:

So fasting raises growth hormone levels? Interesting. So does weight lifting. I’ll bet fasted weight workouts would be pretty powerful.

They do, and they are.

What’s even better is to work out in a fasted state and keep fasting after the workout. This keeps the GH spike going even longer. And in my “just so story” imagination—which is actually quite accurate, judging from real world hunter-gatherers—it mirrors the circumstances of our Paleolithic ancestors. You’d get up early to go hunting without having eaten. You’d expend a lot of energy on the hunt. You’d make the kill, procure the food. And then you’d bring it back to camp to finally eat. Maybe you’d pass the heart and liver around the circle before heading back. And sometimes, you just didn’t make the kill. You didn’t eat at all.

Makes sense, right? Fasting, doing something physical, and continuing to fast shouldn’t be a monumental undertaking. It should be well within the realm of possibility for the average person.

Now, I wouldn’t do this all the time. There is such a thing as too much of a good thing. A hormetic stressor can become a plain old stressor if it’s prolonged for too long. Instead, I would throw post-fasted-workout fasting in on an occasional basis.

Nor would I expect huge “gains” from this. Physiological growth hormone production won’t make you huge or shredded. In fact, workout-related increases in testosterone and growth hormone don’t actually correlate with gains in hypertrophy. Instead, I’d expect more intangible benefits, things you won’t notice right away. It’s important in cognition. It helps maintain bone health, organ reserve, and general cellular regeneration. It’s great for burning fat.

Growth hormone does way more than promote overt muscular growth.

Steve wrote:

In the linked article it says:

“Endothelial cell dysfunction is an initial step in atherosclerotic lesion formation and is more likely to occur at arterial curves and branches that are subjected to low shear stress and disturbed blood flow (atherosclerosis prone areas) (7,8). These mechanical stimuli activate signaling pathways leading to a dysfunctional endothelium lining that is barrier compromised, prothrombotic, and proinflammatory.

So it seems that endothelial disfunction comes first, triggered by blood flow stresses. It’s common wear and tear in exposed areas. The patched knees on jeans. Managing endothelial health and healing may slow or diminish rate of progression or is it mostly too late for that?

I’m not a doctor. This isn’t medical advice. This is just speculation.

I find it rather hard to believe that healthy arteries are inherently fragile and prone to damage and incapable of weathering the “stress” of blood flowing through them, even at the “susceptible” curves. I find it more likely that poor health, poor diets, and poor lifestyles make us more susceptible to otherwise normal stresses.

Do the mechanical stimuli weaken the endothelium in people with healthy levels of nitric oxide production? Or are we talking about people whose poor nitric oxide status is exacerbating the damaging blood flow patterns, leaving their endothelium vulnerable to atherosclerosis?

Think about how much context matters in our response to stimuli. If you’re shy around girls, a school dance will be a traumatic experience. If you’re comfortable around girls, a school dance will be a great experience. If you’re weak, lifting a barbell will be scary, and you may injure yourself. If you’re strong, lifting a barbell will be second nature, and you may get stronger. The baseline context determines the quality of the response.

I’d argue that blood flowing through your arteries should be a commonplace occurrence. It shouldn’t be a traumatic experience. Now, maybe I’m wrong. Maybe it is stressful regardless of the baseline endothelial health and the amount of nitric oxide you produce. Maybe it’s just a matter of time. But:

  • We know that, as you quote, atherosclerosis tends to occur at bends and curves of the arteries—the places most likely to be subject to “disturbed flow” patterns.
  • We know that “laminar flow”—blood flowing smoothly through the artery—is protective of the endothelial wall, promoting anti-inflammatory effects and making the endothelium more resistant to damage.
  • We know that “disturbed flow” has an opposing effect on endothelial health, promoting inflammatory effects and rendering the endothelium more susceptible to damage. This increases atherosclerosis.
  • The question I’m wondering is if “disturbed flow” at the curves and bends of the arteries is inevitable or not. And if disturbed flow is always “bad.”
  • We know that hyperglycemia—high blood sugar—makes disturbed blood flow more damaging to arterial walls. Diabetics have higher rates of atherosclerosis because their elevated blood sugar interacts with disturbed blood flow patterns.
  • We know that nitric oxide increases vasodilation in response to shear stress—widening the arteries to accommodate the increased stress and mitigate the damage done. We know that people with hypertension don’t get the same vasodilatory benefits from nitric oxide.
  • We know that “functional increases” of shear stress attained via exercise increase nitric oxide and oxygen production and induce autophagy (cellular cleanup) in the endothelial walls.

That sounds like there are a lot of factors that increases and mitigate the effects of shear stress on the endothelial wall. It sounds like some factors make shear stress more damaging, and some factors make it less. There may even be factors, like exercise, that make shear stress healthy.

This topic is really pretty interesting to me. It deserves a deeper dive, don’t you think?

What about you, folks? What’s your take on fasted workouts and GH secretion? Ever try one?

And do you think your arteries are doomed to fall apart at the seams?



Nyberg F, Hallberg M. Growth hormone and cognitive function. Nat Rev Endocrinol. 2013;9(6):357-65.

Park SK, La salle DT, Cerbie J, et al. Elevated arterial shear rate increases indexes of endothelial cell autophagy and nitric oxide synthase activation in humans. Am J Physiol Heart Circ Physiol. 2019;316(1):H106-H112.

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