So-called " leaky gut" is hogwash pushed by quacks. It's what influencers push on TikTok or at least their interpretation of it.

https://www.mcgill.ca/oss/article/medical-critical-thinking/...

Sure, leaky gut as a diagnosis is a misapplication for the science. What is real is varying permeability of the intestinal lining in all humans.

Varying intestinal permeability has usually been related to inert compounds. More recently there has been some study on the significance of certain microbe metabolites, but the evidence for any kind of large scale microbial translocation in people that are not very sick (ie septic) is extremely tenuous.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10059777/

"Key controversies in blood microbiome research are the susceptibility of low-biomass samples to exogenous contamination and undetermined microbial viability from NGS-based microbial profiling"

Just because you can amplify some sporadic bacteria DNA from the blood does not mean that bacteria are hanging out in the blood in a physiologically meaningful way.

A lot of it is frankly junk science in disreputable journals.

On the otherhand: https://www.nature.com/articles/s41564-023-01350-w

"Despite this, we found no evidence for microbial co-occurrence relationships, core species or associations with host phenotypes."

"does not mean that bacteria are hanging out in the blood in a physiologically meaningful way."

That's the whole point of this sort of research - to find out if there are physiological connections and what they are.

That’s the purpose of the BBB, which breaks down in hypoxia and cell death.