How old are you? A better question might be: how old do you feel? While your birthday says one thing, your biological age—the health of your cells—might tell a very different story. And here’s the best part: unlike your chronological age, your biological age can go down.

But how? For years, fasting has been celebrated as a key to longevity. Yet the challenge of skipping meals is enough to make most of us shy away. What if you could trick your body into reaping the rewards of fasting—without starving yourself?

This week, we’re joined by Dr. Valter Longo, Director of the Longevity Institute at USC and one of TIME’s 50 most influential people in healthcare. Valter’s groundbreaking research on ageing and his FMD program have transformed how we think about health and longevity. Joining him is Tim Spector, ZOE’s co-founder and one of the world’s top 100 most-cited scientists.