I may be the millionth person to tell you this, but diets do not work, and it's because once the diet comes to an end, you revert back to your old habits - or if not old habits, then you go overboard in some other way. It's all because from the start, you thought of the diet as something that only lasts for a limited period of time. And that is why your subconscious will be telling you continuously during the diet that things will change once the diet ends.
So, instead, think not of a diet, but of a lifestyle - right from the start. This way you won't let your subconscious get any ideas in the first place. Think of the new way of eating as something that will last a lifetime.
Now, you might say that being on a diet for the rest of your life isn't sustainable, and I would understand your point. That is why you must plan the new way of eating in such a way that it is sustainable.
Because you don't have to follow a food lifestyle the way it's described by the inventor to the T. You don't. No one will come to your door and kidnap you and torture you if you have, say, honey on a vegan diet, or sugar during keto.
So find your weak spot - the one thing you think would prevent you from following the new way of eating for the rest of your life. For example, you'd like to go keto, but desire sweet treats regularly. Or you'd like to go vegan, but you know you can't have nuts or vegan cheeses without overeating.
What I suggest is that once a week, on a day of your choosing, you have a special day, during which you can either
- Cast aside the way of eating completely and have whatever you'd like, or
- Indulge in whatever you want to indulge in within your chosen way of eating.
I personally prefer option number 2 because it allows me to feel pride in myself for sticking into a way of life without failure. But that option requires that you don't, ever, indulge in those things on any other day except that special day. If you start indulging within your diet every day, your body will get used to it and it will start to yearn for something more indulging from outside your lifestyle. (Then there are those lucky bastards who can have vegan and keto desserts every day without ever encountering this problem. Kudos to you.)
To walk the walk, I'm going to try this myself - eating according to a very strict but sustainable keto meal plan during the week and then, every Satruday, have sweet keto fudges and fat bombs.
We'll see how it goes.