The Microbiome Diversity Myth: Why More Isn't Always Better

Few ideas in popular gut health have gained the status of unquestionable truth as quickly as this one: more microbiome diversity is always better. Eat diverse foods, take diverse probiotics, live like a Hadza hunter-gatherer — all to maximize the variety of species in your gut. The idea is intuitive, it maps onto general ecological principles, and it's been reinforced repeatedly by wellness influencers and supplement companies with products to sell. But science rarely rewards the intuitive answer in biology. A growing body of research published through 2025 is complicating the diversity-as-gospel narrative in important ways. Context matters enormously. More bacteria in the wrong location isn't a health marker — it's the definition of small intestinal bacterial overgrowth (SIBO). More diversity of certain organisms isn't beneficial if those organisms produce harmful metabolites. And the comparison to traditional hunter-gatherer populations, while conceptually interesting, is riddled with methodological issues. It's time for a more nuanced conversation about what microbiome diversity actually means, when it matters, and when it can be a red herring.

The Conventional Wisdom and Where It Came From

The idea that microbiome diversity correlates with health emerged from a series of important early studies. Research comparing the gut microbiomes of Western populations to traditional communities (the Yanomami in Venezuela, the Hadza in Tanzania, rural populations in Burkina Faso) found that people living more traditional lifestyles had dramatically greater gut microbial diversity than industrialized Westerners — and also lower rates of chronic inflammatory diseases. Studies in C-section-born infants, children raised on antibiotics, and patients with various chronic diseases consistently found lower microbiome diversity compared to healthy controls. The microbiome field enthusiastically embraced diversity as a health surrogate — partly because diversity is relatively easy to measure and partly because it generated a compelling narrative about industrialization, antibiotics, and the epidemics of autoimmune disease and metabolic syndrome that have followed. Low diversity became shorthand for a damaged microbiome. High diversity became the goal.

When 'Diversity' Is the Problem: The SIBO Example

SIBO is perhaps the most striking counter-example to the diversity = good narrative. SIBO, by definition, involves an increased number and sometimes increased diversity of bacteria in the small intestine — a location where bacterial populations should be sparse. A healthy small intestine contains fewer than 10^3 organisms per milliliter of fluid. SIBO is defined by colonization exceeding 10^5 organisms/mL, or by the presence of colonic bacteria (which tend to be species-diverse) in the small bowel. In SIBO, microbial diversity in the wrong anatomical compartment is the disease. Patients with SIBO don't need a more diverse small intestinal microbiome — they need fewer bacteria in the small intestine and restoration of appropriate compartmentalization (large numbers of diverse bacteria belong in the colon, not the small intestine). The same logic applies to other dysbiotic states. Fungal overgrowth (SIFO) involves increased populations of Candida or other fungi — organisms that are normal at low levels but pathological when dominant. H. pylori infection increases a specific bacterial species in the stomach. In none of these situations does 'more diversity' help.

The 2025 Research: Functional Capacity Matters More Than Species Count

A major conceptual shift in microbiome science through 2024 and 2025 has been the move away from species-count diversity (alpha diversity metrics like Shannon diversity index) toward functional metagenomic analysis — asking not how many different species are present, but what metabolic functions those species are collectively performing. This distinction turns out to be critical. Two people can have very different species compositions but nearly identical functional capacities — they have different bacteria doing the same jobs. Conversely, two people with similar species diversity counts can have very different functional profiles based on which bacterial strains are present and which metabolic genes they carry. A 2024 study in Cell Host & Microbe examining over 5,000 individuals found that functional gene diversity was a better predictor of metabolic health outcomes than species diversity alone. The microbiome community most associated with health wasn't the most species-diverse — it was the one most functionally complete, with robust representation of butyrate production, bile acid metabolism, short-chain fatty acid production, and vitamin synthesis pathways. Species richness mattered less than which species were doing the essential work.

Why Hadza Tribe Comparisons Are Misleading

The comparison of Western microbiomes to hunter-gatherer communities like the Hadza of Tanzania has been central to diversity discourse. The Hadza have exceptional microbiome diversity — up to 40% more species than the average American. And they have very low rates of chronic inflammatory diseases. But concluding that microbiome diversity caused their health, or that supplementing probiotics to achieve greater diversity will confer the same benefits, involves several logical leaps. First, the association is confounded by every other way Hadza life differs from Western life: they consume enormous quantities of diverse fiber (150+ grams per day vs. the Western average of 15 grams), they experience dramatic seasonal variation in their diet, they have very different stress profiles, they live outdoors, they consume minimal ultra-processed food, and they've never taken systemic antibiotics. The microbiome diversity is one of dozens of simultaneous differences. Second, the Hadza microbiome includes many species that would be considered pathogens or undesirable in clinical contexts, including heavy parasite loads that are absent in Western populations. Their gut ecology is adapted to their specific lifestyle and environment — transplanting it (or approximating it) to a Western lifestyle may not produce the same health outcomes. Third, Hadza-style diversity correlates with better outcomes at the population level, but individual variation within traditional communities is huge, and some individuals with lower diversity are entirely healthy.

What Microbiome Tests Actually Measure — and Their Limits

Direct-to-consumer microbiome tests (from companies like Viome, Ombre, Thryve, Tiny Health, and others) typically measure gut bacterial composition from a stool sample using 16S rRNA sequencing or shotgun metagenomics. These tests identify which bacteria are present and in what relative proportions. What they don't reliably measure includes what the bacteria are actually doing (functional activity), how individual organisms vary between people with the same genus/species names (strain-level differences can be enormous), what's happening in the small intestine (stool reflects the colon), temporal variability (the microbiome changes significantly day to day based on diet, sleep, and stress), and whether any given species count is optimal for you specifically versus a population average. A 'low diversity' score on a consumer microbiome test is not a diagnosis. It's a single-timepoint snapshot of the colonic bacterial composition using a method that may not capture small populations at all. Many clinicians who regularly order clinical-grade microbiome testing (like the GI-MAP or Genova's GI Effects) interpret results in the context of specific marker patterns rather than as a diversity score.

What Actually Supports a Healthy Gut Microbiome

Rather than chasing a diversity number, the evidence most clearly supports building a functionally healthy microbiome through dietary and lifestyle practices. Dietary fiber remains the single most powerful lever for supporting beneficial gut bacteria — not because it increases diversity counts specifically, but because it feeds the bacteria that produce butyrate, acetate, and propionate, which have wide-ranging positive effects on gut barrier function, immune regulation, and metabolic health. Variety in fiber sources (from different fruits, vegetables, legumes, whole grains, and fermented foods) does support species variety, but the mechanism of benefit is functional, not just numerical. Fermented foods — kimchi, sauerkraut, yogurt, kefir, miso, kombucha — have been shown in a 2021 Stanford study to increase microbiome diversity and reduce inflammatory markers in healthy adults more effectively than high-fiber diets alone, though both approaches have benefits. Minimizing unnecessary antibiotic exposure, reducing ultra-processed food consumption, getting adequate sleep, managing chronic psychological stress, and regular physical activity all support microbiome resilience through mechanisms that are well-characterized and independent of diversity metrics. For SIBO patients: focus on treating the overgrowth, restoring appropriate compartmentalization, and then rebuilding the colonic microbiome through the approaches above. A functional, stable, appropriately located microbiome is the goal — not the highest diversity score.

**Disclaimer:** This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting any new treatment or making changes to your existing treatment plan.