I think diet and eating is only one part of the picture. I'm not so certain about fasting, though. Mind you, a lot turns on how active you are. People, usually men, who do heavy manual work need a lot more to eat than someone like me, who could easily get by on two meals a day, which I try to do. Of course, few actually do heavy manual labor anymore? No matter what I eat, though, if I eat more than I need to, I'll gain weight. I suspect that serious changes in one's weight may be harder on your system than what one weighs to begin with. I for one, however, cannot afford to lose much weight. It just isn't there.
Okay, here's the naturist part again (not the nudist part). I believe it is essential to maintain an active outdoor lifestyle as much as possible. It isn't always possible, of course, given that we usually have to work for a living. And I've known more than a few ladies who lived to a respectable old age without having an active outdoor life. But ask any housewife if keeping a house is active or not.
By an active outdoor life, I just mean getting outside and doing something every day, like going on a good walk. I don't care for tramping around on the sidewalk, like my wife does (she walks a lot more than I do) but I'm lucky in that there are woods behind my house, giving me the opportunity to take about a two-mile walk through the woods, which is just about right. I see a lot of people out walking, and some running, too. I just don't see the grossly overweight people that Americans are supposed to all be these days. But perhaps they all stay indoors. The dog walkers are out, too, and it's said a dog is good because it gets you outside everyday.
So, I don't think there are any secrets to be found or magic pills. There's a certain amount of effort you have to expend, naturally. You can't simply have the perfect diet and just sit there. Dick Van Dyke says you have to keep moving. That may be easier said than done. It's good for your joints if you don't overdo it and it's good for your digestion as well as your appetite. Some old book says a little wine might be good, too. I know next to nothing about things like yoga and calisthenics, while probably the best thing you could do, just seems so old-fashioned. Doing manual work is good in more ways than one. If you aren't doing some manual labor, that is, doing something with your hands, you're living the life of cattle.
Most of what's in this thread belongs in the other one about "if you thought clothing was bad." These things happen. Older outdoor manuals never mention sunscreen or sunblock except in a mountaineering context. Suntan lotions have been around at least since the war and the kind that lifeguards sometimes put on their noses is older. The old manuals always mention insect repellant and some of those concoctions sound like they would be reasonably good sunblocks, too. But the kind of insect repellants we use have been around longer than most of us have, except in aerosol cans. It isn't like people were always well dressed, either. One pre-war writer mentions hiking without a shirt but I don't remember what he said about sun tans and the like.