Your brain has its own immune system, and whether those immune cells protect your brain or attack it depends largely on your metabolic health, which you control with what you eat, how you move, how you sleep, and even the air you breathe. Dr. David Perlmutter is a board-certified neurologist and six-time New York Times bestselling author of Grain Brain, Brain Maker, Drop Acid, and now Brain Defenders. He explains how microglia, the brain's immune cells, shift from brain defenders to brain destroyers when your metabolism breaks down, and why that shift sits underneath Alzheimer's, Parkinson's, multiple sclerosis, and even depression. The conversation covers the diet pillars that keep blood sugar in check, why you need both cardio and strength training, how poor air quality and poor sleep feed inflammation, and the tests that show where you stand long before your memory slips. He closes with his three strategies for wellness: have fun, stay socially connected, and take charge of your own health destiny. Time Stamps: 05:47 How Brain Defenders ties together Grain Brain, Brain Maker, and Drop Acid 08:14 Immunometabolism: why metabolism affects every organ 10:08 The gut microbiome and the brain 11:12 How AI is connecting the dots across specialties 14:54 Microglia: the brain's own immune system 19:12 How metabolism flips microglia from defenders to destroyers 21:37 Type 2 diabetes, blood sugar, and choosing your diet 22:48 Fiber, polyphenols, protein, and dietary fat 25:56 The Mediterranean diet and the Ornish and Tanzi study 27:40 Cardio vs. strength training, myokines, and BDNF 30:50 Flexibility and balance training to avoid injury 32:21 Air quality, PM2.5, and air purifiers 34:23 Why sleep matters for your brain 40:34 Sleep latency and melatonin timing 42:11 Tests to track your metabolic and brain health 44:53 Vitamin D and K2 46:38 3 strategies to get and stay well Links: Dr. David Perlmutter: drperlmutter.com Brain Defenders (book and ordering bonuses): braindefenders.com 40+ Fitness coaching (2 slots open, 16 weeks plus 2 freeze weeks): email coach@40plusfitness.com