Forty men in a 2019 study revealed a clear link: greater bacterial diversity in the colon correlated with longer, more efficient sleep.
Researchers used actigraphy devices and stool samples to find that specific bacterial families, particularly Bacteroidetes and Firmicutes, were associated with better sleep architecture. This moved the field from animal models to human data.
The mechanism is the gut-brain axis. Gut bacteria produce short-chain fatty acids like butyrate, which reduce inflammation and help produce neurotransmitters like GABA and serotonin. Most of the body's serotonin is made in the gut.
A 2025 review in Brain Medicine confirmed these patterns in larger populations, linking lower microbial diversity to conditions like insomnia and sleep apnea. Reduced diversity is often tied to sub-clinical inflammation from a compromised gut barrier.
Diet is the primary intervention. Bacteria that improve sleep thrive on dietary fiber from diverse plant sources like lentils, oats, and vegetables. Fermented foods also boost diversity. Alcohol and chronic stress reduce it.
While the relationship is bidirectional-poor sleep also alters the gut-the consensus is clear. The gut-sleep axis represents a non-pharmaceutical pathway to better rest, with the colon responding to consistent habits over time.