Gut Health, How Exercise Changes Your Microbiome, & More

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My guest on today’s show, Lucy Mailing, Ph.D., is a microbiome researcher, educator, and passionate scholar of integrative, evidence-based gut health.

Lucy received her bachelor’s in biology from Kalamazoo College in 2015. In 2019, she received her Ph.D. in nutritional sciences from the University of Illinois, where her graduate research focused on the impact of diet and exercise on the gut microbiota.

She has authored numerous peer-reviewed journal articles, regularly presents at national and international conferences, and was named an Emerging Leader in Nutritional Sciences by the American Society for Nutrition in 2017. Lucy is the founder and sole author of, a website dedicated to integrative, evidence-based articles about the gut microbiome, health, and nutrition science.

During this discussion, you’ll discover:

-Why Lucy usually skips breakfast in the morning…6:25

  • More productive on an empty stomach
  • Rhonda Patrick recommends women don’t intermittent fast longer than 10-12 hrs (potential for endocan disruption/leptin issues)
  • Intermittent, 24-hour, 7-day water fasting helped Lucy with chronic eczema
  • Physical activity and body type play a role in the need for, and frequency of, fasting

-How Lucy developed her interest in the workings of the gut…9:35

  • The pharmaceutical route proved ineffective in treating her eczema
  • Became familiar with the paleo movement in 2014; saw the connection between gut, diet, and skin health
  • Mark Sisson, Chris Kresser, Sarah Ballantyne were influential
  • Began Ph.D. program at University of Illinois studying the gut microbiome
  • Worked as research assistant for Chris Kresser
  • Book: The Dietary Cure for Acne by Loren Cordain
  • Gut/skin axis plays a role in things like acne
  • The long journey to recovery from eczema provided many opportunities for experimentation and evidence-based research
  • IBS provided further opportunities for expanding her understanding of the gut/diet connection

-The oxygen/gut dysbiosis connection…14:35

  • Article: The oxygen-gut dysbiosis connection: What causes gut health to go downhill, and how to break the cycle of gut inflammation, dysbiosis, and epithelial energy starvation.
  • Butyrate is a short-chain fatty acid, a metabolite produced from the bacterial fermentation of dietary fiber
  • Butyrate provides 70% of the cellular energy for the cells that line the gut and form the gut barrier
  • Fatty acid oxidation: the mitochondrial aerobic process of breaking down a fatty acid into acetyl-CoA units
  • Gut epithelial cells use oxygen from the bloodstream to metabolize butyrate
  • A study at the University of Colorado Denver found that butyrate is required for maintaining the hypoxic state of the colon
  • When butyrate was wiped out with antibiotics, the gut stopped using oxygen and consumed glucose instead
  • The oxygen built up and spilled into the gut lumen (where the microbes hang out)
  • The switch in epithelial cell metabolism from metabolizing butyrate to glucose is a primary cause of gut dysbiosis
  • BGF podcast with Joel Greene (part 1 and part 2)
    • High intake of butyrate via supplementation may actually be feeding cancer cells or resulting in some gut dysbiosis
  • Butyrate supplementation should be done only when not producing enough butyrate or not getting enough ketones
    • Supplementation as an alternative if suffering from gut dysbiosis and can’t tolerate fermentable fiber
    • Doses similar to what the gut naturally produces

-How to test butyrate levels and hypoxic status…21:40

  • Fecal butyrate (looking for butyrate-producing microbes)
  • Onegevity (use code BEN20 to save $20)
  • GI Effects (clinical markers)
  • Low butyrate levels indicate a need for increased fiber intake, or supplementing/ketogenic diet if one has SIBO
  • ProButyrate and Butycaps Tributyrin butyrate supplements
  • Inflammation inhibits the growth of butyrate-producing microbes
  • Mucosal hypoxia is the desired effect
    • Butyrate-producing bacteria are all anaerobes

-Other ways to support gut hypoxia and peroxisome proliferator-activated receptor (PPAR) gamma activation…25:55

-Why the paradigm of how we view SIBO has been misguided…31:15

  • A lot of early research was based on culture-based tests which skew the types and abundance of bacteria found
    • A lot of microbes that live in the small intestine don’t grow in culture
  • Dr. Purna Kashyap: Symptoms of GI disorders indicate small intestinal dysbiosis, not overgrowth
    • It’s not that we have too many microbes in the small intestine, it’s that we have the wrong balance of microbes
  • Tendency to overdo antibiotics
  • Small intestine issues can be misattributed to the large intestine, and vice versa
  • Focus on modulating the entire ecosystem to a healthier state
  • We don’t want to be in colonic energy starvation
  • Taking butyrate supplements while on antibiotics helps maintain hypoxia in the gut
  • Glutamine, bone broth, and colostrum help heal the lining of the gut
  • Decoction tea recipe (instructions on how to prepare)

-Whether a ketogenic diet is good or bad for the gut…37:35

-How exercise impacts the gut microbiome…45:50

-Resistant starch and gut health…54:45

  • Resistant starch is a starch that is resistant to digestion in its host (the human being); passes thru the GI tract to the colon where it can then be fermented by bacteria into short-chain fatty acids like butyrate
  • 4 primary types of resistant starches:
    • RS1, found in whole or partially intact grains, seeds, legumes
    • RS2, present as raw granules (raw potatoes, green bananas, raw plantains)
    • RS3, retrograded starch – retrograde resistant: starches that are cooked and then cooled
    • RS4, chemically-modified starch (synthetic RS; high maize corn starch)
  • Benefits and cautions regarding resistant starch:
    • Blood sugar regulation
    • Increases production of butyrate in some individuals
    • RS2 can potentially increase gut inflammation and microbial cell damage, increase biomarkers of colon cancer
    • RS3 is more familiar from an ancestral standpoint

-What Lucy is excited about regarding gut health research…1:00:30

  • Virtual Microbiome Summit that Lucy hosted (use code BEN20 to save 20% on the recordings)
  • Understanding industrialization of microbiota
  • Using microbiome to predict medical outcomes

-And much more!

Click here for the full written transcript of this podcast episode.

Resources from this episode:

Lucy Mailing

– Book: The Dietary Cure for Acne by Loren Cordain

– BGF podcasts and articles:

– Lab Tests:

– Supplements:

– Other resources:

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Do you have questions, thoughts, or feedback for Lucy Mailing or me? Leave your comments below, and one of us will reply!

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