Overall diversity

Reduced richness is a hallmark of active disease across nearly all cohorts.

Lower diversity tracks the metabolic-syndrome cluster across populations.

Reduced diversity accompanies more advanced disease.

Lower diversity associates with atherosclerosis, alongside the TMAO metabolite pathway.

Reduced diversity and fewer SCFA producers are linked to higher blood pressure in humans and models.

Reduced diversity is consistent even independent of accompanying IBD.

Low diversity in the immature preterm gut precedes the catastrophic inflammation.

Reported both reduced and unchanged; a major confounder is restricted diet, which itself reshapes the microbiome.

Reduced diversity is reported, but Alzheimer’s microbiome research is young and largely associative.

A reduced-diversity gut signature is part of the emerging gut–skin axis.

Reduced early-life gut diversity is one of the most reproducible predictors of atopic disease.

Low gut diversity in the first 100 days of life is linked to later asthma risk.

Low early-life diversity is repeatedly tied to the development of food allergy.

A collapse in diversity removes ‘colonization resistance’ and lets C. difficile take hold; restoring it is curative.

Reduced gut diversity is repeatedly reported and correlates with androgen levels.