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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