It's a mixed bag as I understand it. Some things recover quick and some take much longer, many years of changed lifestyle.

It's got me more interested in health and biology for sure. The human body is remarkably hackable.

Things like bone density and tendon health definitely change slowly. Superficial organ fat, the most dangerous type, is apparently the first thing to go, and you can get so it won't go on quickly again. That's what the cold swimming is for, something to do with types of fat metabolics. I think being overweight for a considerable time (a few years) may have given me joint damage, knees maybe, but TBH I've not pushed myself into injuries and I think it's all strengthening well. I may move to some light strength training soon, but I prefer bodyweight only. Getting to the state where you can even do bodyweight, like 20 press-ups, is a great target.

If you're thinking about doing this... DO IT. I wish I could be beside you on some long walks. Maybe talk to the doc first and set a reasonable plan. But the fasting is not as hard as you think. After the first couple times it gets old and you start to make friends with hunger.

And what ever you improve, whether it's lasting or not, that's gotta be good right?