"In addition, we believe gut microbiota produce proteins that can be present in the blood longer term and modulate pathways in the brain," Fetissov pointed out. In the laboratory, Fetissov and colleagues found that after 20 minutes of consuming nutrients and expanding numbers, Escherichia coli (E. coli) bacteria from the gut produce different kinds of proteins than they did before their feeding.
The 20 minute mark seemed to coincide with the amount of time it takes for a person to begin feeling full or tired after a meal. Excited over this discovery, the researcher began to profile the bacterial proteins pre- and post-feeding.
They saw that injection of small doses of the bacterial proteins produced after feeding reduced food intake in both hungry and fed rats and mice. Further analysis revealed that "full" bacterial proteins stimulated the release of peptide YY, a hormone associated with satiety, while "hungry" bacterial hormones did not.