A longevity expert has named the superfood that is a 'cornerstone of every blue zones diet.' Dan Buettner is a National Geographic Fellow who has spent decades studying 'blue zones', the geographic areas with the world ’s highest proportions of centenarians. He is also a New York Times bestselling author. As part of his work, Buettner regularly answers questions about his own diet and the lifestyle changes he has incorporated into his daily routine based on his research. Speaking to Meat Free