NIH reports that cutting calories by two-thirds, contrary to what you might expect, might not add years to your lifespan:
Scientists have found that calorie restriction—a diet comprised of approximately 30 percent fewer calories but with the same nutrients of a standard diet—does not extend years of life or reduce age-related deaths in a 23-year study of rhesus monkeys. However, calorie restriction did extend certain aspects of health. The research, conducted by scientists at the National Institute on Aging (NIA) at the National Institutes of Health, is reported in the August 29, 2012 online issue of Nature.
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NIA researchers also found that while calorie restriction had a beneficial effect on several measures of metabolic health and function in monkeys who were started on the special diet regimen during old age (at 16 to 23 years), it did not have the same positive outcome for monkeys started on calorie restriction at a young age (less than 14 years).