Podcast: Kaeberlein on rapamycin, aging biology and uncertain longevity claims

What if the most promising drug for slowing aging already exists.. but we still do not know whether healthy people should take it? For decades, Dr. Matt Kaeberlein has studied the biology of aging and the molecular pathways that determine how quickly organisms lose function over time. His work has focused heavily on mTOR, rapamycin and the mechanisms that may allow us to slow biological aging. In this episode of Return on Health, hosts Niko Hems and Miguel Medina challenge Matt on how far the science has actually come. They discuss why aging is far more complex than fixing individual “Hallmarks of Aging,” why changing a biomarker does not necessarily change disease risk, and why interventions that work remarkably well in mice can still leave us with major uncertainty in humans. The conversation then turns to rapamycin. Matt explains why he considers it one of the strongest interventions ever studied for slowing aging in laboratory animals, what decades of human use can tell us about its safety, why longevity dosing differs from transplant medicine and what evidence currently exists for benefits in healthy adults. They also discuss rapamycin and muscle growth, chronic inflammation, ME/CFS and Long COVID, as well as why Matt personally uses rapamycin periodically. The episode also takes on some of the biggest claims in longevity: NAD supplements, biological-age tests, longevity escape velocity and the idea that AI may soon “solve” aging. Matt explains why many popular longevity interventions remain far ahead of the evidence — and why consumer biological-age clocks, in his view, are currently better treated as entertainment than medical tools. ━━━━👤 ABOUT THE GUEST━━━━━ Matt Kaeberlein, PhD is a scientist studying the biological mechanisms of aging and interventions that may extend healthspan. His research has focused extensively on mTOR signaling, rapamycin, cellular aging and the molecular pathways that regulate lifespan. He is also a co-founder of the Dog Aging Project, one of the largest efforts studying aging in companion dogs, with the goal of understanding how genetics, environment and interventions influence healthy lifespan. ━━━━🎙️ ABOUT THE HOSTS━━━━ Niko Hems is Head of Strategy & Medical Communications at YEARS, a preventive medicine company using longitudinal and multi-modal health data to make prevention more personalized and data-driven. Miguel Medina is co-host of Return on Health, a podcast built around a simple idea: a system produces the outcomes it is incentivized to produce — so better health outcomes require better incentives. ━━━━⏱ CHAPTERS━━━━━ 00:00 Who Is Matt Kaeberlein? 00:26 What Actually Is Aging? 02:51 Are the Hallmarks of Aging Causes — or Consequences? 06:57 Why Fixing One Biological Pathway May Not Fix Disease 12:17 What Happens If We Completely Fix One Hallmark of Aging? 14:43 What Is mTOR — And Why Does It Matter for Longevity? 19:48 Is mTOR Bad for You? 22:40 Rapamycin, Muscle Growth & Sarcopenia 26:11 How Should People Think About Longevity Interventions? 28:11 Why Matt Distrusts Certainty in Longevity 30:35 NAD Supplements: Where Is the Human Evidence? 32:53 Why Taking 20 Supplements at Once May Backfire 35:38 How Strong Is the Evidence for Rapamycin? 38:00 Why Rapamycin Is Different From Most Longevity Drugs 39:07 Rapamycin Side Effects Explained 41:29 What Do We Actually Know From Human Studies? 43:43 Rapamycin, Dementia Risk & Chronic Inflammation 45:56 Why Matt Personally Uses Rapamycin 46:39 Rapamycin for ME/CFS & Long COVID 48:49 What Is Autophagy? 51:05 Did Rapamycin Really Improve Chronic Fatigue? 54:36 Why Study Aging in Dogs? 58:44 Where Are the Biggest Opportunities in Longevity? 59:51 Is Longevity Escape Velocity Scientifically Plausible? 01:01:10 Are Biological Age Clocks Useful — or Mostly Marketing? 01:03:19 Which Biological Aging Biomarkers Does Matt Trust? 01:06:18 Rapamycin vs GLP-1s vs Metformin 01:07:07 What Would Matt Change About Healthcare? ━━━━━💡 KEY QUESTIONS ANSWERED━━━━━ • What actually causes biological aging? • Are the Hallmarks of Aging causes, consequences or both? • Why is mTOR one of the most important pathways in aging research? • Can rapamycin actually slow aging? • How strong is the human evidence for rapamycin? • What side effects should people know about? • Does rapamycin interfere with muscle growth? • Could rapamycin help people with chronic inflammation or ME/CFS? • Is autophagy really responsible for rapamycin’s effects? • Is there good evidence that