I don't really know if it only works in the short term, but a diet that basically allows you to eat as much as you want as long as it's meat, veg, seeds, nuts, tubers and fruits, has quite a decent variety for you to choose from. Eliminating carbs from wheat is the mainstay and they argue that for thousands and thousands of year, man lived as a hunter gatherer and we it would be more natural for us to eat like that. It is only fairly recently in the human timeline of existence that we actually increase our dependancy on grain.
But during all those hunter-gatherer years, people lived in a calorie-poor environment. They certainly weren't able to eat as much as they wanted, and they had to work very hard to get it. Certainly they didn't get it sitting at a desk.