Can cutting calories really extend your life? Yes, say a bunch of very old, very hangry monkeys.

For years, scientists at the University of Wisconsin-Madison and the National Institute on Aging ran dueling calorie-deprivation tests on primates, which live to an average age of 25, to see if less food equals longer life. They agreed that cutting calories by 30% improved the monkeys’ health (by cutting cancer and heart-disease risk), but on living longer, they didn’t see eye to eye. 

But not long ago, they came to their senses, pooled their data, and finally announced this: Yes, eating less upped the monkeys’ lifespan about 15%, but only if: 1) their calories were restricted starting at an older age (post-teens was best), and 2) they ate whole, nonprocessed foods. 

But what constitutes “less food” for primates like us? Calorie-restriction cheerleaders advise cutting food intake by about 20%. Any more, and—unless malnutrition is your goal—you’ll want to discuss with your doc first.

Of course, if you don't want to live longer, here's how to do it.