Research on gut bacteria has turned up some interesting and somewhat unexpected results.
Certain bacteria are necessary for humans to digest food. But we don't all have the same bacteria. Although the research found people possessed the "same core group of bacterial genes" needed for digestion, those genes in common were provided by different ranges of bacteria species.
The study also found people who were related shared a similar set of species of gut bacteria. There are several possible explanations for that including, I presume, inheritance via shared environment.
Analysis also indicated that obese people had a greater proportion of bacterial genes for digesting fat, protein and carbohydrates - ie they were better able to extract and store energy from food. If this proves significant, it has strong ramifications for the management of obesity.
The study, written up in Nature, was headed by Jeffrey Gordon of Washington University School of Medicine (Missouri), reported in New Scientist, 8-Dec-08.