The less you eat, the longer you will live. When researchers feed monkeys and rats 30% less than the average monkey or rat eats, these animals live significantly longer. Now before you start cutting back all the calories, know that this hasn't been proven in humans, but this approach to longevity (known as calorie restriction) has the most promise of any methods for extending life.
Of course, you need to make sure that the remaining 70% of your calories contain all of the nutrition that you need to keep yourself healthy. There are people who are trying to live this way. They aren't old enough yet to know if it is doing any good (though they have nice arteries without a lot of cholesterol).
Must Read: Calorie Restriction for Extending Life