Four bacterial groups share one intestinal habitat and compete for the same carrying capacity — a classic logistic-competition model with diet-dependent growth rates.
dN⁏/dt = r⁏(diet)·N⁏·(1 − ΣN⁏ /K) − d·N⁏
H = −Σ p⁏ ln p⁏ (Shannon diversity, p⁏ = N⁏/ΣN)
- Fiber intake — fuels Bacteroidetes and Bifidobacterium, who ferment it into short-chain fatty acids (SCFA) that lower gut pH and suppress pathobionts.
- Sugar & processed fat — favors fast-growing, sugar-loving Proteobacteria and starves the fiber fermenters — the classic route to dysbiosis.
- Antibiotic course — instantly kills ~75% of every population; Proteobacteria (often antibiotic-resistant) recovers fastest afterward, so diversity can crash even after the drug is gone.
- Probiotic — a continuous supplement influx of live Bifidobacterium, helping diversity recover after a disruption.
Real-world relevance: this is why a course of antibiotics or a low-fiber, high-sugar diet can trigger a lasting drop in gut diversity linked to inflammation, weakened gut-barrier integrity and metabolic disease — while a fiber-rich diet or probiotics can help restore it.