Bacteria and obesity

I am a nerd and therefore I have read a lot of sci-fi,  a lot of which has plot based on someone trying to take over the world.  Perhaps this is why I like bacteria so much.....because they already have taken over the world.  

How? They can kill us off and regularly do....Our food and water supplies are somewhat at their mercies...and a lot of the new technology we are developing actually comes from bacteria ....drugs....detergents....alternate energy sources...most of these have components produced by bacteria.  It appears that they may have also taken over our bodies.  This shouldn't be too surprising because a normal human body contains more bacterial cells than human cells and that is bound to have some effect.  One of the ways that our bodies might be affected by bacteria is that they might affect our energy uptake.  This makes sense, because most of them live in our guts,  where we absorb energy.

Okay, so this is the story.  Our gut bacteria are comprised of lots of different types of bacteria, but two of the most important are the firmicutes and the bacteroidetes.  Lean people have lots of bacteroidetes and obese people have lots of firmicutes.  If an obese person starts eating a lot of vegetables, the s/he will experience a change in gut bacterial composition.  More bacteroidetes will become present and there will be fewer firmicutes.  So you may think to yourself that this is an effect of a healthier diet and that weight loss is also a direct effect of the healthier diet.  However, if you take bacteria from the guts of an obese mouse and stick them into the gut of a lean mouse, the lean mouse gains a lot of weight....kind of scary.  

This makes me want to eat lots of vegetables so that I can keep a healthy population of bacteria in my gut.