TOD
Well, believe it or not, the one diet that has ever worked for me was what I was then calling the Atkins Diet. I first tried it in summer of 2001. I had an early version of his book that I sort of half-read. But the theory made sense to me, and I happen to love the kinds of foods you can eat to your heart's content, and I did lose -- I don't remember specifically now, but I'm thinking it was 15 pounds in several weeks and a few more after that.
And did I gain it back? Yes, after a while, because -- wait for it -- I gradually got lazy and returned to my former eating habits. You reap what you sow, I think someone said once. But I did it, again successfully, a couple of other times, and believe you me, it's time for another go at it. And like BK says, at this age you really have make a diet work because the older you get the harder it is to lose that thing around your waist (for men, at least, I don't know about women).
The thing about Atkins (aka Keto) is that you really must do it in a concentrated way at first or your body won't go into ketosis in which you literally pee out those fat cells. My first time, I got some of those strips -- I think they're actually called keto strips or something like that -- to prove that you're doing just that, and by God, I was doing it. And you can feel the difference in "tightness" and energy.
Like any diet, it works for some and not others. Apparently those of us with O-type blood are prone to doing well on it, and it seems to work for men a little easier than for women. And you have to stay on it. Like any diet, if you simply stop and go back to your old habits, your weight will follow. But here's the thing: After being on it strictly for several weeks or whatever it takes to get the body doing what you want it to, you can begin to introduce more of the "good" carbs into your diet and make it more balanced. You can even splurge once in a great while, because when you go right back to being good, the body will remember and behave appropriately.
Hell, I'd forgotten I have a couple of boxes of Atkins bars in a cabinet that are probably still good. Even if you aren't on the diet, they do make excellent "filling" snacks.