How can diversity and species richness be optimal, but my patient is low in Bifidobacterium or Faecalibacterium?

This is a critical distinction: Diversity doesn't guarantee that keystone functional taxa are present.

Think of it as an ecosystem analogy: A forest can have hundreds of plant species (high diversity) but lack oak trees (keystone species). The forest functions, but differently from one with oaks.

Why this happens:

1. Niche competition:

• Other species fill ecological niches
• May have adequate SCFA production from different organisms (Roseburia, Eubacterium)
• Functionally compensated but missing gold-standard taxa

2. Common causes of keystone depletion:

• C-section delivery (reduced maternal Bifidobacterium transfer)
• Antibiotic exposure (affects beneficial bacteria)
• Low fiber intake (Faecalibacterium requires resistant starch)
• Formula feeding (reduces infant Bifidobacterium dominance)
• Chronic inflammation (creates an unfavorable environment)

Clinical approach:

• High diversity = good foundation to build on
• Target missing keystones with specific interventions based on test results:
  • Bifidobacterium: HMOs (infants), GOS/FOS (adults), Bifidobacterium probiotics
  • Faecalibacterium: resistant starch, inulin, butyrate support
  • Akkermansia: polyphenols, cranberry extract
• Retest to confirm successful colonization