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.
So fasting raises growth hormone levels? Interesting. So does
weight lifting. I’ll bet fasted weight workouts would be pretty
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
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
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
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
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
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.
- 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
- 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
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.
Dear Mark: Fasting, Training, and Growth Hormone; Wear and Tear on
the Arteries appeared first on Mark’s Daily Apple.