Digestion is not performed by human cells alone

The gastrointestinal tract contains microbial communities that participate in digestion and interact with metabolism, immunity and the intestinal barrier. A meal therefore enters an ecosystem as well as a sequence of human organs. Some compounds unavailable to our own enzymes can be transformed by microbial activity.

The microbiome varies greatly between people and over time. Much research identifies associations, while causal pathways and useful interventions remain active questions. A single ideal community has not been established, and commercial tests can outrun clinical meaning. The bounded fact is partnership: normal digestion involves resident organisms, without making every microbe beneficial or every health outcome microbial.