I did multiple 3 day fasts earlier this year, because I was convinced that they're very important to long term health. I didn't do it to lose weight, rather for the purpose of overall health. I had a lipoma that shrank by about half, also a weird scaly area of skin that got completely better. Both of these issues had been around for decades. I also had a few other weird health improvements.

You might want to look at Thomas Seyfried's work. Very interesting. Also Alan Goldhamer. He runs a fasting clinic in CA. It's vegan, and I think he's wrong on veganism being healthier than a whole-foods type diet, but I believe he has some good insights.

Also - look up information on autophagy and fasting. It's really amazing stuff that mainstream science will not and, I believe can not (because of funding sources) ever give us good information on.

Once you're convinced that it's really important and helpful, you do it. And once you've done one or more 3 or 4 day fasts, you will likely have some minor or major health issues improve or clear up completely. Especially if you're older. Autophagy can be amazing.

I think a one day fast is useful, and probably nobody does a longer fast without doing a one day fast, but I think the real benefits come after a few days.

But it's tough. I don't have any weight to lose, so I'm not at all energetic after the first day of a fast. I think it may be easier if you have some extra fat. After day 2, I spent hours looking at recipes online. Didn't get much done (except, hopefully, healing).

I have a recommendation, which is to take some good photos of your hands and face if you have anything like age spots, before fasting. I think some of them disappeared, but I don't know for sure.