ScienceDaily looks at the beneficial effects and mechanisms of calorie restriction and exercise: "We know that being lean rather than obese is protective from many diseases, but key rodent studies tell us that being lean from eating less, as opposed to exercising more, has greater benefit for living longer. This study was designed to understand better why that is ... Rats that exercise regularly will, on average, live longer compared to a group that eats the same amount but does not exercise. This is because exercise prevents some diseases, which allows more individual animals to live out their expected life span. However, when comparing the rats in these two groups that eat the same amount, the longest-lived animals in the exercise group don't live any longer than the longest-lived rats in the non-exercise group. Taken together, these findings indicate that exercise can prevent an early death from disease in some rats, but does not extend the maximal lifespan of any of the rats." The obvious choice for we humans is to both exercise and practice calorie restriction, obtaining all the benefits of both.