There are some serious studies being conducted to confirm the efficacy of tree nuts as a weight maintenance food. The Purdue University study (you can read about it here) is testing to see how such a calorie rich food can help control appetite and contribute to weights loss. There are the obvious suggestions that it is rich in fiber and protein which help satiate, but the study is trying to see if there's some neurological or sociological response to their consumption which can keep people coming back to them instead of going for candy bars.
Another diet trend has its roots in ancient practices. A new trend to weight loss, blood glucose maintenance, and a possible Alzheimer's reducer, is to conduct fasts twice a week. This practice is referred to as 5:2 fasting. The Wall Street Journal recently talked about it, and you can read about it's implementation here. Basically, it's about having zero to 500 calories on fasting days twice each week and eating normally (or abnormally for some people) on "feast" days five times each week.
What's fascinating about this diet trend is how ancient it really is. For Islam, there is a Sunnah practice of Sawm (fast) on Monday and Thursday (You can find out about it here) which are voluntary fasts. In Judaism, the custom of fasting on Mondays and Thursdays is older and has a different meaning, but isn't as regular an occurance as the Sunnah custom in Islam (read more about BeHab in Judaism).