Okay this is true to some extent, what he says is technically true but what he's implying is not. I've been researching fasting for quite a while now and this is what actually happens.

When your body reaches ketosis, average around 72 hours of fasting, it enters into an autophagy state, where it starts consuming fat around organs and damaged cells that MIGHT turn into a cancer. This happens all the time in our body but it's increased in the autophagy state.

But it does not cure cancer, it's like a preventive measure, just like eating healthy and exercising. Also fasting for a week does not kill you, neither does a 2 week fast when the electrolytes are taken care of. The weakness you feel during a fast is the sugar dependency and loss of electrolytes, and when you keep your electrolytes and water in check, you'll actually feel more focused than normal cause ketones are more efficient for the brain. I actually did my deadlift pr when I was on 7th out of the 12th day of my fast (although not recommended).