Parasites · Protozoan (protist)

Blastocystis

Contested The most common gut protist — and the poster child for ‘parasite vs partner.’ Carriers tend to have HIGHER bacterial diversity and leaner, healthier guts, and it’s more common in healthy people than in IBD. Yet some studies link it to IBS.

Associated with these conditions

Inflammatory bowel disease (IBD) Reduced

Consistently LESS common in IBD than in healthy people, hinting at a protective or health-marker role.

Moderate evidence

Irritable bowel syndrome (IBS) Mixed

The contested one: linked to IBS in some studies, yet associated with healthier, high-diversity guts in asymptomatic carriers.

Disputed / mixed studies conflict

Obesity Reduced

Less common in obesity and associated with leaner phenotypes — again pointing to commensal rather than harmful.

Moderate evidence

HIV infection Associated with

Reported in Disbiome.

Preliminary

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