A potential explanation could lie in the trillions of microbes that reside in the gut. In 2009, Rosa Krajmalnik-Brown from Arizona State University in Tempe and her colleagues sequenced the bacterial genes present in faeces from three people who had received a gastric bypass.
Compared with obese and normal-weight controls,
their guts contained
proportionally
fewer bacteria
from the usually abundant Firmicutes phylum
, and excess levels of the Gammaproteobacteria class8. “Even with that small sample size we were able to get statistically significant differences because the microbiota changed so drastically,” Krajmalnik-Brown says.