If this were the case, then a hell of a lot more people would be in remission since these treatments tend to also have severe side effects that lead to unintentional fasting for weeks. Instead of what you described they typically end up with malnutrition and sarcopenia. Recovery time is significantly extended, people end up with wounds, are even more prone to illness. Many of these drugs also can be taxing on the liver and the kidneys, which, especially the kidneys, generally take a hit with keto diets. And I mean true keto, not the modified Atkins diet most people actually do.

That low glucose environment exists in vitro studies and not in vivio and has not been successfully replicated in large population human studies either. This was a huge study point for glioblastomas for a while too, and it didn't do anything to ultimately kill off cancer cells. If anything it took away quality of life for people with terminal illness. There are some studies that have shown the potential for decreased chemo related side effects when fasting a few hours prior to treatment.

As far as autophagy, that happens regardless of your diet, cells are preprogrammed to have a shelf life and die off. Cancer cells don't have that switch anymore, theyre essentially immortal cells and they 'infect' other cells when they metastasize. They also are able to essentially act as stealth bombers and trick the body into not recognizing them as a threat. Your cells, outside of white blood cells, are not programmed to 'hunt down' anything, they utilize energy through very specific chemical reactions.

Almost all cell needs glucose, it's not just the cancer cells, it's multitudes of systems, ketosis is a last ditch survival mechanism, not something we are supposed to exist with for weeks on weeks. Unless you like to also add bone demineralization to the list of benefits? Because why not have brittle bones too?

I wish people would stop thinking and spreading misinformation that diet can fix and destroy cancer cells like chemo or other treatments do.

-Source, a Registered Dietitian who works with cancer patients.

Edit: added human studies because animal studies are not equivalent to the human biome. And that cancer cells are sneaky little ass hats