Is insulin such a big deal?
Trying to get the bioenergetics seems to be too difficult for me. DeFronzo says insulin driven GLUT4-transport is 85% of exercise glucose uptake. At times, I am convinced the story is false. But then, its up to the mitochondria. What could go wrong!
Is it really about the GLUT4?
Howcome neurons get along by using only GLUT3 for their glucose transport, if GLUT4 is such a deal? Seems the brain can utilize some quarter of the body energy budget, wouldn't that also require some fancy receptor activation? (assuming neurons only use GLUT3, and that old story about GLUT4 as the primary glucose transport mechanism. Besides, its a known)
Some research seems to find only percentual increase in muscle power from unblocking GLUT4 receptors. In one mouse study, transgenic GLUT4 deficient mice still had efficient glucose uptake, suggesting mitochondria as the limiting factor. Also problematic to this glucose-with-insulin-GLUT4 idea is evidence of GLUT4 activation after exercise. (assumptions: mice cells are like humans)
It is clearly not just GLUT4
Yet even more problematic frontier is the fact that even in some trained athletes that have diabetes, muscles can function for hours. While its assumed total insulin deficiency will lead to DKA, is there something else going on, aside from the typical powered-by-GLUT4 -story?
Ketones and unknown signals? I suppose the ketone utilization would happen in the same mitochondria, after the same glycogen runs out, given otherwise the same scenario for glucose or ketone use. (how can you tell if its muscle glycogen, liver glycogen, or liver fat, adipose melting or perhaps something else?)
Perhaps more pragmatic evidence could be found by measuring one's blood sugar regularly. Do your muscles power output differ with the blood sugar level? The simple and pragmatic once again is lost, to medical research.
It's really just glycogen burning, isn't it?
Perhaps, its just the post-exercise GLUT-activation product (glycogen). So, most of it isn't blood glucose during exercise, in any case. What a silly framing, as if people would run and eat at the same time! Evans 2019 finds nine GLUTs in human muscle, GLUT1 as basal.
Model of exercise training effect on skeletal muscle GLUT. Image copyright 2019 P.L. Evans, S.L. McMillin, L.A. Weyrauch, C.A. Witczak with Creative Commons Attribution (CC BY) license.
Further, what about GLUT1 to GLUT3, that do not require insulin signals? No, muscles do not need insulin to transport glucose! Base of the transport seems to be passive, only to be boosted by exercise.
Primary effect of insulin and hyperglycemia is fat
How about go interview couple of dozen diabetics first, as a myth busting activity. Just for broader context, ask first where diabetics get amylin?
Then ask, what effect do they get in the injection site of insulin? They do this many times a day, every day, as external insulin is used as primary therapy for Type 1 diabetics. That's a group of several percent of the glopulation, should be easy enough to ask.
Fat in adipose cells
Again another systemic fail happened here: the meganarrative is to ignore the fact that in vivo, insulin signals fat storage in adipose cells. Problematic in the healthy as well, as this causes refined carbs to be stored as fat - because hormones.
Instead the Soda and Donut Companies of the World bought the fake story that calorieisacalorie, and that fat makes you fat. To top it off, the literate MD's repeat confused ideas about muscle glucose uptake - but there's no exercise!
Industries subvert knowledge
Reality is, no way to avoid the ills of contemporary post-industrialized, mediated society. The food and pharma industries have massive influence. Manipulated research, marketed as ground truth: fake diets and medicalization, as never before.
Fat-tissue gains are way more insulin-boosted, than momentary muscle glucose transport in absence of exercise. As if the large amounts of glucose from refined carbs wasn't harmful as such. But the nutrition and medical communities ignored this, or simply could not comprehend the fact. Result: global diabetes epidemic.