I think there's a phenomenon that would confound measuring such effects in a population wide epidemiological study: chronic illness (especially cancer) often causes loss of hunger, and automatic calorie restriction.

In general, I think the "lipostasis system" which regulates hunger in humans makes long term calorie restriction in healthy individuals very difficult, and very rare.

Probably a good strategy to overcome this obstacle would be to hack the lipostasis system to defend a lower body fat setpoint, with techniques such as a very low food reward diet (links: (http://boingboing.net/2012/03/09/seduced-by-food-obesity-and-t.html) (http://sethroberts.net/)).