#379 - AMA #79: A guide to cardiorespiratory training at any fitness level to improve healthspan, lifespan, and long-term independence

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter In this "Ask Me Anything" (AMA) episode, Peter brings together his most up-to-date thinking on cardiorespiratory fitness into a single, practical guide designed to help listeners structure training for maximal impact on healthspan, lifespan, and long-term independence. He explains why cardiorespiratory fitness is one of the strongest modifiable predictors of longevity, clarifies what zone 2 training actually represents and how it differs from higher-intensity work, and addresses persistent confusion around exercise volume, intensity, and time constraints. The discussion covers how to measure and track progress in zone 2, VO₂ max targets and age-adjusted goals, planning for the marginal decade, and how to balance zone 2 with higher-intensity training across different weekly volumes. Peter also outlines how cardio training should be tailored for beginners, experienced trainees, and older adults, with special considerations for women and guidance on avoiding the most common cardio-training mistakes. If you're not a subscriber and are listening on a podcast player, you'll only be able to hear a preview of the AMA. If you're a subscriber, you can now listen to this full episode on your private RSS feed or our website at the AMA #79 show notes page. If you are not a subscriber, you can learn more about the subscriber benefits here. We discuss: Rational for discussing cardiorespiratory fitness, zone 2, and VO₂ max despite having covered the topic extensively [2:30]; Why cardiorespiratory fitness and VO₂ max are powerful and modifiable predictors of all-cause mortality compared with other health metrics [7:30]; How age-related declines in VO₂ max constrain healthspan and everyday physical function [12:30]; The cardiorespiratory fitness triangle: how different training intensities contribute to building the aerobic base, the aerobic peak, and overall aerobic capacity [14:15]; The cellular mechanics of cardiorespiratory fitness: mitochondria, lactate, muscle fiber recruitment, and intensity thresholds [18:45]; The debate over whether zone 2 training has unique benefits or whether higher-intensity exercise alone is sufficient [27:15]; Balancing intensity and sustainability as training volume increases, and the important role of zone 2 training [32:15]; How to identify your zone 2 training intensity [34:45]; How to measure and track improvements in zone 2 fitness [40:00]; How to accurately measure VO₂ max: lab testing, field tests, and the limits of wearables [45:15]; How to set meaningful VO₂ max targets based on age, sex, long-term decline, and desired physical capabilities later in life [51:15]; How to structure and execute a zone 2 workout [59:45]; How strictly should zone 2 be maintained during a workout? [1:04:00]; How to design a VO₂ max training session: interval length, intensity, recovery, and progression strategies [1:07:00]; Why heart rate is not a reliable metric for titrating VO₂ max interval intensity [1:12:00]; Practical ways to monitor VO₂ max improvements [1:13:30]; How to balance zone 2 and VO₂ max training [1:15:30]; How to structure training for someone limited to 150 minutes per week of total exercise [1:19:00]; How to allocate 150 minutes per week of dedicated cardiorespiratory training between zone 2 and VO₂ max work [1:23:00]; How to structure training for someone with substantial available time who wants to maximize cardiorespiratory fitness [1:24:30]; Why spreading aerobic training across the week beats compressing volume into one session [1:26:15]; How beginners and metabolically unhealthy individuals should start cardiorespiratory training safely [1:28:00]; How "training age" determines the intensity and workload needed to continue improving cardiorespiratory fitness [1:31:15]; Why zone 2 training still matters for women (including postmenopausal women) [1:32:45]; How cardiorespiratory training should adapt with aging [1:35:45]; The most common mistakes people make when training cardiorespiratory fitness and how to avoid them [1:37:45]; How to break through a VO₂ max plateau [1:40:45]; The main takeaways about cardiorespiratory fitness and longevity [1:41:30]; Peter's carve out: oral hygiene and Peter's two-toothbrush system [1:43:00]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Abbie Smith-Ryan is a leading researcher in exercise physiology whose work focuses on how training and nutrition influence body composition, metabolism, cardiovascular health, and women's health across the lifespan, with particular attention on perimenopause and post-menopause. In this episode, Abbie explains how early exercise and play help build the foundation for bone health, muscle development, and cardiorespiratory fitness in girls, as well as how puberty and menstruation shape athletic performance, motivation, and recovery. She also explores how women can tailor training and nutrition across the menstrual cycle through smart fueling, hydration, and inflammation management; examines the evidence behind supplements such as creatine, omega-3s, and magnesium; and unpacks the metabolic and body composition changes that accompany the transition into perimenopause and menopause. Finally, she covers practical exercise programming for busy women, training and nutrition considerations during pregnancy and postpartum, and the evolving role of hormone therapy alongside lifestyle-based, evidence-driven approaches that help women better advocate for their health. We discuss: Abbie's background in distance running and her interest in studying women's health around exercise [3:00]; The role of early-life exercise in building lifelong bone, muscle, and cardiovascular health in girls [4:00]; Training principles for premenstrual girls, the risks of early specialization and delayed puberty from intense training, and how youth sport participation can shape bone and spinal health [7:15]; Nutrition as fuel in young female athletes: supporting training, growth, and performance [11:00]; Training and recovery across the menstrual cycle: recovery, nutrition, supplements, and practical strategies for performance support [16:00]; The benefits of creatine supplementation and importance of protein intake across the menstrual cycle [27:15]; How women should approach training intensity and volume across the menstrual cycle [33:00]; How to identify and monitor the perimenopausal transition and why this phase represents a critical window for exercise and nutrition interventions [37:15]; Case study: time-efficient exercise program for a busy, perimenopausal woman [42:00]; Why improving body composition is a better goal than weight loss, and how to set realistic fat-loss targets in midlife women [53:30]; How to preserve muscle and bone while using GLP-1 medications: resistance training, protein intake, and more [58:15]; Designing a three-hour-per-week training plan for sustainable body recomposition [1:03:30]; Abbie's insights from her 20+ years of self-tracking: nutrient timing, injury prevention, excessive training, bone health, and more [1:07:15]; How pregnancy and the postpartum period affect body composition, and how consistent exercise and intentional nutrition can prevent a permanent shift in body fat or muscle mass [1:13:30]; Changes in muscle quality and metabolic flexibility during perimenopause and menopause, and how exercise may counteract hormonally driven sarcopenia [1:21:45]; The biggest open questions about women's health: combining menopause hormone therapy with exercise, GLP-1 drugs, minimizing injury risk, and more [1:32:00]; How the training response differs between men and women, and the importance of type IIa muscle fibers [1:39:15]; Training advice for the hypothetical 70-year-old woman who has never exercised deliberately [1:47:00]; Misinformation about exercise and nutrition for women, injury risk, supplement hype, and the need for more nuanced messaging around hormones, recovery, and midlife training [1:53:30]; Benefits of hormone therapy in midlife women and its interaction with exercise and lifestyle interventions [2:00:15]; Peter's overall take on how women should approach exercise volume and intensity at various life phases and time constraints [2:03:00]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter James Clear is the author of the New York Times bestseller Atomic Habits. His extensive research into human behavior has helped him identify key components of habit formation and develop the "Four Laws of Behavioral Change." In this episode, James provides insights into how both good and bad habits are formed, including the influence of genetics, environment, social circles, and more. He points to changes one can make to cultivate more perseverance and discipline and describes the profound impact habits can have when tying them into one's self-identity. Finally, James breaks down his "Four Laws of Behavioral Change" and how to use them to create new habits, undo bad habits, and make meaningful changes in one's life. We discuss: Why James became deeply interested in habits [1:45]; Viewing habits through an evolutionary lens [6:00]; The power of immediate feedback for behavior change, and why we tend to repeat bad habits [9:15]; The role of genetics and innate predispositions in determining one's work ethic and success in a given discipline [14:30]; How finding one's passion can cultivate perseverance and discipline [23:15]; Advantages of creating systems and not just setting goals [29:15]; The power of habits combined with self-identity to induce change [36:30]; How a big environmental change or life event can bring on radical behavioral change [50:30]; The influence of one's social environment on their habits [54:15]; How and why habits are formed [1:00:30]; How to make or break a habit with the "Four Laws of Behavior Change" [1:09:30]; Practical tips for successful behavioral change—the best strategies when starting out [1:16:15]; Self-forgiveness and getting back on track immediately after slipping up [1:30:30]; Law #1: Make it obvious—Strategies for identifying and creating cues to make and break habits [1:39:45]; Law #2: Make it attractive—examples of ways to make a new behavior more attractive [1:47:45]; Law #3: Make it easy—the 2-minute rule [1:58:45]; Law #4: Make it satisfying—rewards and reinforcement [2:03:30]; Advice for helping others to make behavioral changes [2:06:00]; More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter In this special episode of The Drive, Peter presents a curated "best of" conversation with bestselling author and previous guest Arthur Brooks, organized around four core themes: happiness itself, the forces that undermine it, the tools and practices that help cultivate it, and the courage required to live and love well. The episode brings together the most meaningful moments from two past interviews into a single, focused discussion that distills Brooks' most insightful ideas and offers practical takeaways for building a life that's both successful and deeply happy. We discuss: Happiness vs. happy feelings, and how happiness and unhappiness can coexist [2:15]; The six fundamental emotions [5:30]; The three main "macronutrients" of happiness [15:00]; Enjoyment: one of the three macronutrients of happiness [22:45]; Satisfaction: one of the three macronutrients of happiness [30:45]; Sense of purpose: one of the three macronutrients of happiness [38:45]; Fame: one of the traps that hijack our happiness [46:30]; Success addiction, workaholism, and their detriment to happiness [49:15]; The reverse bucket list: one of Arthur's tools and practices he recommends for moving past the traps that hijack our happiness [59:15]; Metacognition: one of Arthur's tools and practices he recommends for moving past the traps that hijack our happiness [1:01:00]; Taking charge of your happiness: discipline, transcendent experiences, and other deliberate actions for "happier-ness" [1:11:30]; Tracking happiness: the biomarkers and micronutrients behind the macronutrients of happiness [1:22:45]; The value of minimizing the self and looking outward [1:30:45]; How Arthur surprised himself with his ability to improve his happiness [1:34:45]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter In this "Ask Me Anything" (AMA) episode, Peter tackles a wide-ranging set of listener questions spanning lifespan interventions, exercise, cardiovascular risk reduction, time-restricted eating, blood pressure management, hormone therapy, diagnostics, and more. Peter reveals the single most important lever for extending healthspan and lifespan, and explains how he motivates midlife patients using the Centenarian Decathlon framework. He discusses the importance of addressing high apoB and cholesterol even in metabolically healthy individuals with calcium scores of zero, how to manage high blood pressure, and how to accurately evaluate metabolic health beyond HbA1c. Additional topics include time-restricted eating, practical considerations around ultra-processed foods, nuanced approaches to HRT for women and TRT for men, and why early and expanded screening for chronic disease—colonoscopy, PSA, coronary imaging, low-dose CT—can be lifesaving. He also offers insights into treating prediabetes, crafting exercise programs for those short on time, and safely incorporating high-intensity training in older adults. If you're not a subscriber and are listening on a podcast player, you'll only be able to hear a preview of the AMA. If you're a subscriber, you can now listen to this full episode on your private RSS feed or our website at the AMA #78 show notes page. If you are not a subscriber, you can learn more about the subscriber benefits here. We discuss: Introducing a wide-ranging AMA: practical perspectives on lifespan interventions, metabolic health, diet, hormones, diagnostics, and more [2:45]; Why exercise is the most powerful single intervention for lifespan and healthspan [4:15]; How Peter motivates midlife patients to prioritize exercise [6:00]; Why lifespan and healthspan should not be treated as competing priorities and how choosing sustainable interventions benefits both [9:30]; Why high apoB deserves treatment even in a metabolically healthy patient with a CAC score of zero [14:00]; Managing hypertension: ideal targets for blood pressure, lifestyle levers, and why early pharmacology matters [18:15]; Assessing metabolic health beyond HbA1c: fasting insulin, triglycerides, lactate, zone 2, and more [23:30]; How to avoid common self-sabotaging patterns by choosing sustainable habits over extreme health interventions [26:00]; Time-restricted eating: minimal effect beyond calorie control, implications for protein intake, and practical considerations for implementing it [28:00]; Ultra-processed foods: definitions, real-world risks, and practical guidelines for smarter consumption [30:30]; How women should prepare for menopause and think about hormone replacement therapy: early planning, symptom awareness, and guidance on HRT [36:45]; Testosterone replacement for aging men: indications, benefits, and safe clinical management [39:45]; Why Peter recommends earlier and more aggressive screening tests than guidelines suggest: colonoscopies, coronary imaging, PSA, Lp(a), and low-dose CT scans, and more [43:30]; Full-body MRI screening: benefits, limitations, potential false positives, and the importance of physician oversight [47:15]; Prediabetes: individualized treatment strategies using tailored combinations of nutrition, sleep, and training interventions [51:00]; Time-efficient training plans for people with only 30 minutes per day to exercise [53:00]; How to safely introduce high-intensity exercise for older adults [55:00]; Timed dead hangs and ripping phone books: a playful look at Peter's early attempts to impress his wife [57:15]; Peter's carve out: The Four Kings documentary about a golden era of boxing [1:01:15]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Dom D'Agostino is a neuroscientist and professor at the forefront of metabolic therapies, including ketogenic diets, exogenous ketones, and hyperbaric oxygen. In this episode, Dom breaks down nutritional versus supplemental ketosis, defines meaningful ketone thresholds, and outlines practical ways to achieve ketosis. He explains how a ketogenic diet can support metabolic health and weight loss, and advises on how to maintain adequate protein and avoid common mistakes. Dom surveys the growing landscape of exogenous ketones—from salts and esters to 1,3-butanediol—and effective pairings like caffeine, MCT oil, and alpha-GPC. He highlights the role of ketogenic therapy in cancer (particularly glioblastoma) and its promise for neurodegenerative diseases. The conversation also covers recommended hyperbaric oxygen protocols for brain injuries and cognitive function, situations where fasting or ketones offer cognitive and anti-inflammatory benefits, and touches on the carnivore diet as a ketogenic variant with potential relevance for autoimmune and metabolic conditions. We discuss: Dom and Peter's shared interest in ketosis, and Dom's scientific journey [2:30]; Dom's work for the Navy on oxygen toxicity [7:00]; Nutritional ketosis defined: physiology, biomarkers, and how fasting and diet generate therapeutic ketones [15:00]; The historical roots of ketogenic diets in epilepsy treatment, and evidence showing ketones reduce seizure activity and strengthen brain resilience [19:00]; Dom's personal experience on the ketogenic diet: tracking macros, getting enough protein, and monitoring ketone levels [24:15]; Using a ketogenic diet for weight loss: Dom's guidance on protein, fiber, calorie tracking, lipid monitoring, and more [31:00]; Protein on ketogenic diets: Dom's rationale for higher intake and muscle preservation [38:00]; Incorporating carbohydrates into keto: timing, high-fiber foods, and other considerations [41:30]; The carnivore diet: whether this diet induces ketosis, how it functions metabolically, and why it may help individuals with autoimmune conditions [44:15]; Early exogenous ketones: how 1,3-butanediol works, its liver toxicity risk, and why ketone esters replaced it [48:15]; The progression of exogenous ketones: why BHB monoesters and ketone salts emerged as better alternatives to 1,3-butanediol for ketone supplementation [59:30]; Ketone salts: easing the transition into ketosis, dosing, and how they compare to ketone esters [1:04:00]; The differences between D- and L-β-hydroxybutyrate, and how racemic mixtures may elevate ketones longer and offer unique biological effects [1:09:30]; How ketosis may boost NAD, and why NAD supplements have fallen short so far [1:16:30]; Emerging evidence for using a ketogenic diet to treat anorexia and other psychiatric disorders [1:20:30]; Potential cognitive and performance benefits of ketone supplementation, and why pushing ketones too high can be dangerous [1:23:45]; Applications for ketone esters, and why ketone salts or MCT-blended formulations may be safer and more practical for most people [1:29:15]; The role of a ketogenic diet in treating cancer [1:34:45]; The potential of a ketogenic diet for treating Alzheimer's disease [1:45:45]; Tools for cognitive enhancement: ketones, alpha-GPC, MCT, caffeine, strategic fasting, and more [1:53:45]; Hyperbaric oxygen therapy for concussion, TBI, PTSD, and cognitive function, including protocols and dosing approaches [1:55:30]; Peter's takeaways, recommended products, and additional resources to learn more [2:03:00]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Carole Hooven is a human evolutionary biologist whose research centers on testosterone, sex differences, and behavior. In this episode, she explores how prenatal testosterone orchestrates male development in the body and brain, how early hormonal surges shape lifelong behavioral tendencies, and what rare natural experiments—such as 5-alpha-reductase deficiency—reveal about the biology of sex differentiation. She discusses distinct male and female aggression styles through an evolutionary lens, how modern environments interact with ancient competitive drives, and the implications of attempting to suppress them. The conversation also covers testosterone across the lifespan, the role of hormone therapy in both men and women, and Carole's own experience after surgical menopause, culminating in a broader discussion of masculinity, cultural narratives, and the consequences of denying biological sex differences. We discuss: How Carole became interested in exploring the biological and evolutionary roots of sex differences and the role of testosterone [2:30]; How testosterone and other hormones influence sex differences in aggression and behavior across species [9:45]; How chromosomes, the SRY gene, and early hormones direct embryonic sexual differentiation [12:15]; A stark contrast of male social bonding compared to females, and evolutionary parallels in chimpanzees [19:30]; How hormones like DHT shape sexual differentiation, and how 5⍺-reductase deficiency reveals the distinct roles of these hormones [22:45]; How sex chromosomes and prenatal testosterone shape early brain development and explain sex differences in childhood behavior [31:30]; How gamete differences shape reproductive strategies, energetic costs, and sex-specific behavior [42:30]; How evolutionary biology shapes sex differences in play, aggression, and conflict resolution (and how modern environments and cultural messaging can disrupt those patterns) [49:00]; Why males commit disproportionately more violent crime, and how cultural and environmental forces shape aggression [1:01:00]; Why females evolved different behavioral strategies: nurturing, risk aversion, and the cultural norms that override biology [1:04:00]; Whether male aggression is still necessary in modern society, why the underlying biological drives persist, and how modern society redirects these drives [1:06:30]; How testosterone levels naturally shift to support fatherhood and caregiving [1:13:30]; How testosterone shapes male mating strategies, and why long-term pair-bonding persists even when reproduction is no longer at stake [1:18:30]; The distinct roles of estrogen in male development, mood, libido, and muscle [1:25:00]; How evolution, health, lifestyle, and androgen receptor biology shape modern testosterone replacement therapy (TRT) [1:34:15]; Carole's experience with hormone replacement therapy (HRT), and the risks associated with TRT in younger men [1:45:15]; How Carole rebuilt after controversy: leaving academia and recommitting to scientific honesty [1:51:30,]; Carole's next book: examining masculinity, cultural narratives, and the cost of denying biological sex differences [1:57:30]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Walter Green is a remarkable philanthropist, mentor, author of This Is the Moment!, and founder of the impactful "Say It Now" movement. In this episode, Walter delves into the unique insights gained from his challenging upbringing, discusses embracing mortality, and highlights the mindset of "finishing strong." He shares insights on intentionality, thinking in reverse, saying "no," prioritizing relationships, and the essence of focusing on others. The conversation focuses on the "Say It Now" movement, which stresses the importance of expressing sentiments to loved ones well before the end of life. We discuss: How Peter and Walter met through Ric Elias [3:30]; The unique perspectives and life lessons provided by Walter's challenging childhood [6:00]; Walter's harrowing experience with a sudden mental breakdown and his subsequent recovery with the help of therapy [12:15]; A diverse professional journey ending in great success [19:15]; The birth of a movement: celebrating friendships through public tributes and expressing gratitude to those who have shaped your life's journey [23:30]; Intentionality, thinking in reverse, saying "no", and other guiding principles for Walter [30:45]; Walter's global journey of gratitude on his 70th birthday, visiting friends, and creating memorable experiences [40:15]; The profound impact of acknowledging and expressing gratitude for the people who contribute to our lives [47:15]; The key elements for creating meaningful connections and cultivating deep, authentic friendships [53:15]; The "Say It Now" movement: the inspiration behind the remarkably impactful initiative [59:15]; What "finishing strong" means to Walter [1:08:15]; Finding peace at the end of life through expressing gratitude and finding purpose in serving others [1:16:45]; Resources to learn about "Say It Now" [1:27:00]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Antonio Bianco is a world-renowned physician-scientist and expert in thyroid physiology and metabolism. In this episode, Antonio explores the complex biology of thyroid hormone production, conversion, and regulation—highlighting how deiodinase enzymes modulate hormone activity at the tissue level and why that matters for interpreting lab results. He discusses the shortcomings of relying solely on TSH as a marker of thyroid function, the ongoing debate around combination therapy with T3 and T4 versus standard T4 treatment, and how genetics, tissue sensitivity, and individual variability influence thyroid hormone metabolism. The conversation also examines how hypothyroidism affects energy, mood, cognition, and longevity; why some patients remain symptomatic despite "normal" labs; and how future research could reshape treatment paradigms. We discuss: How the thyroid produces, stores, and activates hormones like T4 and T3 to finely regulate thyroid activity [2:45]; How fasting alters thyroid hormones to conserve energy [12:45]; Action of the deiodinases: how D1, D2, and D3 enzymes control the activation and inactivation of thyroid hormones [19:15]; The normal function of thyroid hormone and the roles of the hypothalamus, pituitary gland, and deiodinases in maintaining hormonal balance [23:30]; Why understanding thyroid physiology is essential for proper diagnosis and treatment of hypothyroidism [33:45]; Testing for thyroid hormones: understanding free vs. total levels, the limitations of current T3 assays, best practices, and more [36:00]; Genetic and sex-based variability in thyroid hormone regulation and their limited clinical significance [43:45]; Hyperthyroidism: causes, symptoms, diagnosis, and treatment options [46:00]; Hypothyroidism: diagnosis and autoimmune causes of hypothyroidism [56:30]; More on hypothyroidism: diagnostic biomarkers, antibody patterns, and non-autoimmune presentations [1:05:00]; Thyroid hormone replacement therapy [1:15:15]; More on thyroid replacement strategies: exploring the evidence gaps, mortality signals, effects on lipids, and more [1:28:00]; Hypothyroidism basics: causes, antibody implications (including pregnancy), and how to make the diagnosis before choosing therapy [1:35:15]; Thyroid medication: compounded controlled-release T3, brand name versus generic, and what Antonio prescribes to newly diagnosed hypothyroid patients [1:42:45]; Redefining treatment success: why normalizing TSH isn't always enough for patients with hypothyroidism [1:54:45]; Case studies: analysis of two unusual cases of thyroid disease [1:57:00]; Dangers of supplementing with high levels of iodine, and female-specific risk of thyroid disease [2:05:45]; Case study of a patient who presents with elevated TSH but no symptoms [2:09:30]; How future research could reshape treatment, and Antonio's new book called "Rethinking Hypothyroidism" [2:13:15]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube

View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter In this "Ask Me Anything" (AMA) episode, Peter breaks down the science of dietary fiber, moving beyond the blanket advice to "eat more fiber" to uncover what it actually does in the body and where its benefits are truly supported by evidence. He explains how different types of fiber—soluble, insoluble, viscous, and fermentable—affect digestion, satiety, weight management, and glycemic control, and compares their impact to other, more potent metabolic tools. Peter also examines how certain fibers influence lipid metabolism and cardiovascular risk, evaluates the strength of evidence for fiber's role in colorectal cancer prevention, and highlights why some individuals may not tolerate specific fibers well. The discussion concludes with practical guidance on moving past generic fiber targets toward a more strategic and personalized approach that maximizes the true benefits of fiber. If you're not a subscriber and are listening on a podcast player, you'll only be able to hear a preview of the AMA. If you're a subscriber, you can now listen to this full episode on your private RSS feed or our website at the AMA #77 show notes page. If you are not a subscriber, you can learn more about the subscriber benefits here. We discuss: Why it's time to re-examine the evidence behind dietary fiber recommendations [2:00]; Why it's hard to isolate fiber's true effects on health: the limits of nutritional epidemiology [5:45]; Defining dietary fiber: what it is, how it's digested, and why different types have different effects [8:15]; Understanding fiber properties: how solubility, viscosity, and fermentability shape its effects in the body [11:15]; Resistant starches explained: types, food sources, and how cooking and cooling influence their benefits [16:30]; A framework for evaluating each of the major health claims linked to fiber [19:15]; How fiber can support weight loss: mechanisms, realistic expectations, and its complementary role to broader dietary strategies [20:30]; How fiber modestly improves glycemic control by reducing glucose spikes and insulin demand [26:15]; How fiber modestly lowers LDL cholesterol and supports cardiovascular health [34:30]; How fiber compares to other available tools and strategies for managing lipids, blood sugar, and weight [42:00]; Fiber's role in colon cancer prevention: mechanisms, evidence, and limitations [45:30]; Is fiber necessary for colon cancer prevention in otherwise healthy individuals? [53:30]; Why some people have adverse reactions to certain types of fiber, and how to manage them [56:00]; A general strategy for dietary fiber: combine multiple fiber types through whole foods and supplements [58:45]; Why total fiber intake is more important than the ratio of soluble-to-insoluble fiber [1:02:45]; The optimal timing and context for consuming fiber to maximize blood sugar control and metabolic benefits [1:05:00]; How food processing affects the functional properties of fiber, the differences between supplement forms and natural sources, and why whole foods generally remain the best option [1:06:45]; Fiber's potential to interfere with medication absorption [1:09:30]; How to safely increase fiber intake: ramp up gradually and stay hydrated [1:12:00]; Final takeaway on fiber: modest benefits, strong rationale, low downside [1:13:00]; Peter's carve-out: lessons and inspiration from the Acquired podcast [1:14:30]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube