Intermittent fasting - actually I'm pretty skinny already and losing muscle through less exercise so I actually want to gain a couple kilos

Ha ha, I don't do it to lose weight, but rather to give my gastrointestinal tract a rest periodically, which can only be a good thing in my opinion. There are tribes who have a fast day every tenth day and I find a lot of the stuff tribes do is derived from wise knowledge passed down over centuries.

On the cold water showers, ya, even doing 30 seconds at the end will do you good, fair play to you.