Prebiotics vs probiotics: trial comparison

In this episode, I return to a conversation I promised to continue - sitting back down with Prof Tim Spector, MD, to explore everything that has changed in microbiome science since Episode 224. Tim and the ZOE team have now published a landmark Nature paper with 34,000 microbiome samples, run a clinical trial comparing personalized nutrition against government guidelines, and Tim has published a book on fermentation science.

We cover why most probiotics are scientifically obsolete, a practical ranked guide to fermented foods, the TMAO pathway linking gut bacteria to cardiovascular risk, and the estrobolome - the gut bacteria that recycle estrogen in women. If you have the gut health basics in place, this conversation tells you what to prioritize next.

What We Cover

• The ZOE Microbiome Health Ranking 2025: what 34,000 gut microbiomes revealed about the species that actually matter
• A practical guide to fermented foods: how much, how often, and whether pasteurised versions count
• The TMAO mechanism - how your gut bacteria may influence the cardiovascular risk of red meat
• Why most probiotic supplements use strains that are 100 years out of date
• The estrobolome: how gut bacteria control estrogen recycling in women
• The menopause - microbiome connection and what ZOE's latest research shows

Building a healthier gut microbiome is less about one dramatic intervention and more about consistent, moderate changes compounding over time. This conversation gives you the clearest picture yet of which changes to prioritise.

To connect with the guest, follow Tim Spector on Instagram at @tim.spector and explore ZOE at zoe.com.

• Intro (00:00)
• Why Gut Diversity Is a Flawed Metric (01:58)
• Does the Microbiome Actually Cause Disease? (15:23)
• Vegan vs. Omnivore Microbiomes (26:52)
• Why ZOE Made Their Research Public (31:49)
• Prebiotics Beat Probiotics in RCT (39:46)
• The Case for More Fiber (46:43)
• How to Buy Fermented Foods (53:32)
• Resistant Starch vs. Polyphenols (59:42)
• Are "Natural" Sugars Any Different? (01:03:12)
• Time-Restricted Eating & the Microbiome (01:11:21)
• What's Next for Zoe Research (01:18:35)

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This episode is brought to you by:

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Simon Hill, MSc, BSc (Hons)

• Creator of theproof.com
• Host of The Proof with Simon Hill
• Author of The Proof is in the Plants

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Nourish your gut with my Plant-Based Ferments Guide and download my Two-Week Meal Plan.