The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome.
Level 1 - systematic review of randomized trials
Systematic review of comparative and observational literature across species (graded by design analogy, not clinical CEBM).
PubMed 26222383 · doi:10.1371/journal.pone.0134116
What was done
The authors conducted a systematic review across mammal and bird taxa to test whether vertebrate stomach acidity functions as an ecological filter shaping gut microbial communities. They compared stomach acidity across trophic groups (scavengers, carnivores, herbivores, and carnivores feeding on distantly related prey) and evaluated within-species variations in stomach acidity, such as with age or bariatric surgery.
What was found
The abstract reports no numerical values, pH ranges, or statistical effect sizes. It reports that scavengers and carnivores have significantly higher stomach acidities than herbivores or carnivores feeding on phylogenetically distant prey (e.g., insects or fish), and that intraspecific changes in gastric acidity correspond with shifts in gut bacterial pathogens and communities.
Why it matters
This work supports an evolutionary role for gastric acidity as a pathogen filter rather than solely a digestive mechanism, emphasizing the importance of gastric pH in human and comparative microbiome studies.
Limits
The abstract provides no sample sizes (number of studies or species evaluated) and no numerical data or confidence intervals. Comparative cross-species and observational data are subject to residual confounding across divergent physiology and diet.
Cited by
- supports Normal physiological human gastric pH ranges from 1.2 to 1.3, which is the third or fourth lowest stomach pH among animal species.