Calorie restriction has been shown to extend life in several types of animals including worms, flies and mice. The question was whether it would work on humans. Given that such an experiment would take decades to conduct and carry a lot of ethical baggage, scientists turned to monkeys and started experiments in the late eighties. Well the results are in and the answer is probably not. A study just out in Nature (link here) finds that rhesus monkeys that were given a reduced calorie diet did not live longer. This contradicts a previous study from the University of Wisconsin published in Science in 2009 (link here) which did show caloric restriction extended life of monkeys. However, in that study, monkeys that died due to causes that were deemed unrelated to aging were not included. Here is a New York Times summary. There are some people who are currently limiting their diets in an attempt to live longer so perhaps we will have some unofficial data points on humans in few decades. My guess is that there will not be a net increase in humans since lifespan is a complicated thing and there are always tradeoffs. Caloric restriction may be protective in some aspects but it may also be detrimental in others.