Flex Diet Podcast

In this episode of the Flex Diet Podcast, I sit down with Dr. Sara Campbell, Ph.D., Associate Professor at Rutgers University, for a conversation about the bidirectional relationship between exercise and the gut microbiome.

Dr. Sara Campbell returns to discuss her lab's cutting-edge research on the bidirectional relationship between exercise and the gut microbiome — including why consumer gut tests oversimplify a complex ecosystem, how antibiotics devastate exercise capacity in animal models, and why single-microbe probiotics miss the bigger picture of functional guilds. She also shares new findings on short-chain fatty acids, amino acid metabolomics after antibiotic treatment, and the emerging neuromuscular junction hypothesis.

In this episode you'll learn:

Why consumer gut microbiome tests are misleading and what functional guilds tell us instead

How antibiotics devastate exercise capacity and the surprising metabolomic changes they cause

The current evidence on probiotics for exercise performance and why single strains fall short

What short-chain fatty acids do for gut health and exercise, and the emerging neuromuscular junction hypothesis

Find Sara here:
Rutgers Faculty Page

Google Scholar: Sara Chelland Campbell

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The Flex Diet Podcast is brought to you by the Flex Diet Certification. Learn more at miketnelson.com

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In this solo episode, Dr. Mike T. Nelson dives into the intersection of AI and coaching. Using his quest to pick up the 175-pound Inch dumbbell as an example, he shows how AI struggles with niche topics where quality training data is scarce — and why that matters for fitness advice.

Topics covered:

Why AI gave terrible advice on training for the Inch dumbbell — and what that reveals about how AI sources information

The protein-and-kidney-damage myth: when AI repeats bad science

Where AI actually helps coaches: data analysis, blood work organization, backend tasks, and production workflows

Why clients still want (and need) a real human coach — accountability, customization, and skin in the game

Will people be compliant to a robot coach? Probably not

The baseline is rising: why just writing training and nutrition programs isn't enough anymore

Flex Diet Certification — now open through Monday, June 22nd, 2026 at midnight PST. Eight interventions (protein, fats, carbs, exercise, sleep, micronutrition, fasting, and more) built on coaching leverage and metabolic flexibility. Includes direct email access to Dr. Nelson for enrolled students.

Enroll now: https://miket.me/fdc

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Dr. Emily Dow, PhD, RD, is a researcher and registered dietitian working at the intersection of nutrition, resistance training, and gut health.

Does vinegar actually do anything for your gut or your blood sugar? Can you trust a $200 mail-in microbiome test? Emily built her dissertation around questions like these, and her honest answers are a lot more useful than the marketing.

Expect to learn what a 12-week resistance-training-plus-vinegar protocol did (and didn't do) to gut permeability, why a null result in a healthy population is still worth your attention, what the research really says about vinegar and glucose control, why the peptide boom warrants a hard dose of skepticism, what direct-to-consumer gut testing genuinely can and can't tell you, the underrated role stress plays in GI symptoms, and why the best practitioners do both research and hands-on coaching — and much more.

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Connect with Dr. Dow: Website: https://www.dremilydow.com Instagram: https://www.instagram.com/dremilydow

Episodes you'll enjoy next: #127 — The Effect of Antibiotics on Muscle Mass & Cardiovascular Performance with Dr. Sara Campbell: https://flex-diet-podcast.simplecast.com/episodes/episode-127-the-effect-of-antibiotics-on-muscle-mass-aerobic-cardiovascular-performance-and-more-an-interview-with-dr-sara-campbell
 #222 — Nutrition, Supplements & Training with RD Sean Casey https://flex-diet-podcast.simplecast.com/episodes/episode-222-expert-insights-on-nutrition-supplements-and-training-with-registered-dietician-sean-casey

Enjoying the show? Follow the Flex Diet Podcast in your podcast app so new episodes land automatically — it's the single best way to help others find it.

Timeline 

0:00 Intro

02:29 Vinegar Research Origins 

04:12 Study Design & Training Protocol

07:42 Biodex Explained: Strength Testing 

11:49 Research Tradeoffs & Null Results 

14:49 Possible Mechanisms: Acetate 

19:55 Glycemic Control & CGM Findings 

22:21 Peptides: Hype and Risks 

28:54 Microbiome & Performance Research

30:47 Gut Testing Skepticism 

36:23 Stress and GI Symptoms 

39:22 PhD to RD Fast Track 

41:04 RD Exam Reality Check 

44:25 Scope of Practice Basics 

45:56 Referral Networks That Work 

49:29 Research vs. Coaching Gap 

58:51 Clients Drive Better Questions 

01:05:26 Why She Started Instagram 

01:09:58 Social Media for Academia 

01:13:18 Training Goals and Tattoos 

01:15:45 Where to Follow & Wrap Up

 

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In this episode of the Flex Diet Podcast, I sit down with Dr. Nathan Jenkins to discuss how to improve performance, body composition, and long-term health through the lens of aerobic development and metabolic flexibility.

Nathan shares his journey from exercise physiology and coaching CrossFit athletes to his new role teaching physiology at the University of Georgia School of Medicine. We discuss why metabolic flexibility is such a powerful framework for understanding everything from biochemistry and exercise performance to metabolic disease.

We also dive into interpreting maximal exercise testing data, including VO₂ measurements, EKG analysis, and near-infrared spectroscopy (NIRS), along with how different energy systems work together during training and competition. Nathan explains why building an aerobic base is critical for repeated high-intensity performance, how pacing impacts outcomes, and why the ability to "suffer" is actually a trainable skill.

To wrap up, we cover practical strategies you can apply right away, including prioritizing protein and carbohydrates, improving sleep quality, and addressing common micronutrient deficiencies through blood work, such as magnesium, vitamin D, and omega-3 status.

Sponsors:

Daily Fitness Insider Newsletter: https://flex-diet.kit.com/bfa1510fa8

Available now:

Grab a copy of the Triphasic Training II book I co-wrote with Cal Deitz here.

Episode chapters:

02:47 Meet Dr Nathan Jenkins

04:38 CrossFit Nutrition Reality Check

07:09 Leaving Tenure for Family

09:21 Back to Academia and Med Ed

11:29 Why Exercise Physiology Matters

14:36 Stress Tests Reveal Pathology

18:19 Max Testing and NIRS Setup

22:42 Raw Data Over Machine Outputs

24:18 Bohr Effect and Oxygen Delivery

28:09 Energy Systems in the Real World

33:05 Coaching Basics That Matter

35:40 Teaching Cardio From First Principles

36:36 Aerobic Base Reality Check

37:19 Cardio for Meatheads Pitch

39:13 CrossFit Endurance Breakthroughs

41:49 Fixing Time Domain Weakness

45:46 Pacing Like Froning Fraser

48:42 RAAM Gamesmanship Story

51:45 Pain Management Truths

53:23 VO2 Max Feels the Same

55:54 Suffering as a Skill

59:09 Cold Plunge Mindset Study

01:00:52 Caffeine Placebo and Belief

01:03:22 Heat Acclimation and 10K Prep

01:04:36 Metabolic Flexibility Lens

01:08:16 Teaching Diabetes Integration

01:10:56 Bloodwork Meets Flexibility

01:12:37 Where Fat Goes Wrong

01:15:07 Sustainable Deficit Strategy

01:16:34 Four Priorities Blueprint

01:17:21 Protein and Carb Targets

01:21:08 Sleep and Micronutrients

01:27:06 Omega-3 Testing Nuance

01:29:36 Wrap Up and Next Steps

01:31:52 Newsletter and Flex Diet Cert

01:33:20 Final Thanks and Subscribe

Flex Diet Podcasts you may enjoy:

Episode 344: Metabolic Adaptations, Lactate, and Training Smarter with Dr. Phil Batterson

YouTube: https://youtu.be/PPZyO1nxSPA



Episode 383: Body Composition, Strength Training, and Sustainable Habits with Martin Silva

YouTube: https://youtu.be/p8oM0gW488U



Connect with Dr. Jenkins:

Website: https://www.drnathanjenkins.com/

Instagram: https://www.instagram.com/drnathanjenkins

Get In Touch with Dr Mike:

Instagram: Drmiketnelson

YouTube: @flexdietcert

Email: Miketnelson.com/contact-us

Get the Daily Fitness Insider newsletter (free): https://www.miketnelson.com/newsletter

In this episode of the Flex Diet Podcast, I sit down with my friend Tracy Holemeyer (Uncontrollably Me, host of the Other Way to See It podcast) to talk about healing and performance through nervous system flexibility, somatics, and self-awareness, especially with how much stress people are carrying right now. 

We dig into practical tools like orienting, grounding, the “starfish” drill, pendulation, and Tracy’s “core four” (soft eyes, relaxing the tongue, breath pacing for coherence, and soft knees), plus how posture and unconscious habits can shape mood and behavior. We also explore the value of community and coaching, how movement and sound (including humming, voo breath, and growling) can help regulate, and we finish with a thoughtful discussion on psychedelics, integration, and why support and discernment matter.

Sponsors:

Daily Fitness Insider Newsletter: https://flex-diet.kit.com/bfa1510fa8

Available now:

Grab a copy of the Triphasic Training II book I co-wrote with Cal Deitz here.

Episode Chapters:

02:59 Meet Tracy and Catch Up

04:46 Micro Breaks and Orienting

08:46 Starfish and Body Awareness

10:44 Joints Posture and Anxiety

17:37 Strategies Become Identity

21:00 Awareness Coaching in Practice

26:02 Coaching Community and Support

32:44 Social Media Validation Trap

36:13 Integrity and Business Alignment

39:39 Trauma Weight and Safety

41:57 Referrals Over Scarcity

43:07 Abundance Through Uncertainty

47:09 Money Purpose and Access

52:57 Capacity and Ongoing Stress

57:15 Pendulation and Core Four

01:03:00 Movement Urgency and Sound

01:08:55 Growling Music and Release

01:15:23 Healing as Defiance

01:16:59 Flow States and Community

01:18:23 Recreation With Real Stakes

01:20:13 Choosing Controlled Hardship

01:21:09 Healthy Stress Builds Capacity

01:23:34 Rewriting Trauma Responses

01:25:28 Psychedelics And Integration

01:34:07 Avoiding The Healing Shortcut

01:37:10 Where Memories Live

01:42:45 Four Tools For Stress

01:46:19 Finding Tracy And Closing

01:49:45 Podcast Wrap And Disclaimer

Flex Diet Podcasts you may enjoy:

Episode 354: How Shiftwave Reboots Your Nervous System w/ Dr. Jeff Rouse

YouTube: https://youtu.be/XTPwIb3ZMxQ



Episode 345: Sleep Like a Beast: Lessons from Jay Wiles and Jeffrey Durmer

YouTube: https://youtu.be/8mVvceWn-Yw



Connect with Tracy:

Website: https://www.uncontrollablyme.com/

Instagram: https://www.instagram.com/embodiedsomatics

Get In Touch with Dr Mike:

Instagram: Drmiketnelson

YouTube: @flexdietcert

Email: Miketnelson.com/contact-us

Get the Daily Fitness Insider newsletter (free): https://www.miketnelson.com/newsletter