In the long run, diets don't work. In this study that I've mentioned previously, any of four diets (Atkins, Ornish, Zone, or Weight Watchers) led to only a 5 or 6 lb weight loss over a year's time. Other studies show the same result when they extend the time horizon out to a year or more.
In contrast, you can look at studies where calories were intermittently restricted and you see much better results. By intermittently restricted, I mean that calories are cut fairly low on some days with normal eating on the rest of the days. In the book, "The Alternate Day Diet", the idea is to restrict calories one day and have unlimited eating the next (as the title implies). Others recommend different frequencies as to how often calories should be reduced.
It's important to distinguish between intermittent calorie restriction and intermittent fasting. If intermittent fasting turns into eating a full day's calories in one meal, then there may not be much benefit. For example, if you look at studies on Ramadan fasting where a person fasts until evening but then has a large meal, there often isn't much change in body composition.
I think some of the intermittent fasting studies show benefits only because they indirectly restrict calories on fasting days. If a study has alternate-day fasting, then obviously a person will have no calories on one day. Or if someone fasts until 6 pm, it may be hard to eat enough calories as would normally be consumed in a day's eating.
In "The Alternate Day Diet", the author makes the case that the real benefits come from a 36-hour period of low calories. That is, eating much less one day and then sleeping on it. The benefits aren't dependent on not eating food for some many hours per se, as in one study subjects sipped on a protein shake throughout the day. It's the 36-hour period of low calories that triggers weight loss, and also lessens oxidative stress and inflammation.
What I wonder is why this approach is not more widely known. If you continually restrict calories, your metabolism will slow and the lost weight will come back. If you restrict calories every other day (or every third day or twice a week), then you can lose weight but the metabolism will not adapt and slow down.
It has to be easier psychologically to restrict calories only part-time as well. A lot of times on diets, people too much pressure on themselves and then they break down. With intermittent calorie restriction, you only have to control calories on some days, not all. This seems like a much more livable approach over the long term.