How long do GLUT-4 transporters stay active on muscle after exercise?

(BuckRimfire) #1

In a semi-recent YouTube video about carb cycling, Nick Norwitz suggested that consuming some carbs after exercise would have a modest effect on ketosis since GLUT-4 transporters (insulin-independent glucose uptake proteins) are brought to the muscle surface in reaction to exercise.

This seems plausible if the rate of glucose intake into the muscles can keep up with the release of glucose from the gut. However, if I heard correctly (maybe I should listen to it a 3rd time), he suggested eating high-glycemic-index carbs in this case. That doesn’t make sense to me, since unless we’re talking about a pretty tiny amount of carbs, I would think that would saturate the GLUT-4 uptake and give you enough of a BS spike to induce insulin release. Admittedly, I have no quantitative knowledge of either of those rates (glucose out of the gut and glucose into the muscle).

The other question is how long GLUT-4 transporters stay on the muscle membrane? Until glycogen is repleted, even if there is a delay of an hour or two until you eat, or does the window of opportunity pass quickly regardless?

(Bob M) #2

Good questions. I have tested 100g of rice noodles (a few hours after) (body weight) exercise (to failure), and I was able to stay in “ketosis” (meaning >0.1mmol/l blood ketones). I tried it the next day, however, when I did not exercise, and all the bad parts of high carb came back – I was tired, hungry, etc. (Though I was still in “ketosis” that day and the next. Would be nice to have a continuous glucose monitory though.)

I think the carbs went into my muscles.

My problem is that I work out early in the morning (end around 7am), but don’t eat my first meal until about 10am.

As for all the GLUT-4 stuff, I bet this is probably meaningless for normal people. Nick Norwitz tends to go off the deep end and read too much into single studies. Eg, this ONE study says you should do X!

I’ve also given up on “high glycemic index” anything, because multiple studies of people with CGMs show that different carbs are processed completely differently for different people. What’s “high glycemic” for you might not be for me, and vice versa.