Strong
Fibre is the finding that holds up
Dose-dependent reductions in all-cause and cause-specific mortality across meta-analyses. Most Europeans eat about half the recommended intake.
The gut-brain axis, separated from the marketing
The gut-brain axis is real. Almost everything sold on the strength of it is running years ahead of the human evidence — with one large exception.
81peer-reviewed citations
42European languages
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The short version
Fibre has large, consistent, dose-dependent effects on hard outcomes and almost nobody eats enough of it. Probiotics have small and inconsistent effects on mood. Microbiome testing services have essentially nothing. The gap between those three statements is the whole story of this field.
Weak
Do probiotics affect mood?
Meta-analyses find small effects on depression and anxiety symptoms, in trials with real quality problems.
Mechanism
What the axis actually is
Vagal signalling, microbial metabolites and immune pathways — most of it characterised in rodents.
Caution
Why your microbiome test tells you nothing
There is no validated healthy reference microbiome, and results vary by sampling and sequencing method.
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