What Actually Improves Metabolism as You Age — Ketones, Fasting, and Fueling for Endurance | Dr. Brianna Stubbs

Ketones and fasting get marketed like shortcuts. This conversation is the opposite: a grounded look at how your body actually produces energy—and what changes as you age.Dr. Brianna Stubbs is a researcher at the Buck Institute for Research on Aging and a world-class endurance athlete. We talk about metabolic flexibility (your ability to switch fuels), what ketones can and can’t do, and when fasting helps—or backfires—depending on training load, recovery, and goals.In this episode: What “metabolic flexibility” really means (in plain English)  Exogenous vs. endogenous ketones—and why the difference matters  Fasting, performance, and muscle: where people get it wrong  What endurance athletes can reveal about aging physiology  Practical fueling principles that support longevity—not fads The goal isn’t extreme restriction or constant optimization. It’s building a metabolism that stays resilient, adaptable, and recoverable over decades.Timeline: Support cellular renewal and mitochondrial function with Mitopure, featuring Urolithin A. Get up to 20% off at timeline.com/AGELESSATHLETE 🚀 Love the show? Here’s how to support it If something you’ve heard here has stayed with you, made you smile, or helped you keep going, I’d be honored if you’d consider supporting the show. 👉 https://buymeacoffee.com/agelessathleteTopics: longevity, fitness over 40, endurance training, aging athletes, recovery, injury prevention 💜 Want to stay strong and capable as you age? Join the Ageless Athlete weekly newsletter for practical ideas, deeper lessons, and insights that don’t always make it into the podcast.Join here → https://agelessathlete.substack.com/subscribeAgeless Athlete is a podcast about healthy aging for people who want to stay strong, active and capable for life. Conversations explore strength, endurance, mobility, recovery, VO2 max, muscle and bone health, and what it takes to keep doing the things you love as you get older.Follow Ageless Athlete — How to Stay Strong, Curious & Capable for Life for new episodes each week.