You actually should exercise while fasting. When fasting, t he body gets rid of fat, and any muscles that are not essential. Which makes a lot of sense - maintaining muscle costs both protein and energy, even if they aren’t used much.

I did not try to run quickly while fasting, but I did keep doing my 5km 3 times per week, and the gym. Anaerobic was hard and quickly tiring, but aerobic exercise wasn’t really any harder.

A friend did point out that my movement was “more economical” in general - I hardly lifted my feet while running or walking, and a few other things. But I didn’t feel more tired or more strained, except for unaerobics.

1) there are tons of substances the body can't make out of nothing/lipids. 2) there are tons of substances the body can't make efficiently with no food, which leads to metabolism/health deficits. and no it's not just vitamins and electrolytes LOL it's much more complex and diverse than that.

3) even if we assume in an ideal world, that the person who fast is able to supplement ALL the useful things and yet not take any external calories/glucose. This person would still reach a huge bioenergetic deficit/stress. Yes he will survive as you say, and might even be asymptomatic but nonetheless I would be very surprised if the biomarkers where doing Okay. Default bloodworks analysises are shit but if you command a proper analysis of your antioxidants ratio and of your bioenergetics biomarkers and apoptotic biomarkers you will see (unless I'm wrong which is very unlikely given my expertise) that the body is having a significantly accelerated aging/damage scheme. Which might not show symptoms before multiple decades later and even might not show symptoms at all in his life but statistically, there is a risk. Now he can mitigate some of those, by taking e.g. ALCAR + NAC daily for a year.

BTW the guy you linked died at 50 years old, which is not a performance.

You went from "This guy should be dead" after 30 days of fasting to "this one guy died 25 years after a one year fast".

All I'm saying is that you were wrong. The human body can take much more than you explained in your first comment. You won't die nor fall unconscious and "5-7 days max" isn't anywhere close to the limit

yes I was wrong on the potency of the damages, that does not refute my valid concern about transiently asymptomatic damages.

What are bioenergetics biomarkers and apoptotic biomarkers? Google doesn’t give me a reliable source

There are many. For apoptosis induced by mitochondria deficits you look at the level of cytochrome C. But there are others. For oxidative stress, a good indication is the ratio of reduced glutathione (how much of your antioxidants are being used)

for bioenergetics I don't remember the relevant ones although the manifestation is not only molecular, it can be observed (mitochondria respiration rate, uncoupling, etc) maybe this paper can show the relevant ones? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4715336/

Are you comparing fasting to breathing aluminium particles ?

well I was not, only that between those two stressors, the same major biomarkers are involved. There often is a surprising level of similarities between seemingly distinct things and here I would bet there are possible comparisons however that is not the point of my parent comment, just an answer to which biomarkers are involved. A more direct comparison would be with the acutes and long terms damages of hypoxia, because oxygen is a similar cofactor bottlenecking energy production, as is the absence of glucose/pyruvate from a fasting human which singlehandely rely of lipid/beta-oxidation. e.g. https://pubmed.ncbi.nlm.nih.gov/21542052/ But it's not because those are the same mechanism (a bottleneck on a critical cofactor for ATP) that the effects have the same potency because of course fasting is less dangerous in strength than hypoxia.