How bacteria in your gut could be making you fat, allergic, or anxious

The bacteria in our guts are indispensable.
They help us fight off other, more harmful bacteria and aid in digestion and nutrition. But scientists are also now finding evidence that when our microbial ecosystems fall out of balance, they can end up related to all sorts of problems — obesity, allergies, and possibly even some mental illnesses.
The science around our bodies' "microbiomes" is still quite young — too young to inform medical treatments in most cases. Scientists can't yet draw a direct link between a specific microbe and obesity, or suggest the best diet for the community living in your gut. But what researchers are finding is that these microbes might influence our health far more than anyone realized.

http://www.vox.com/2014/11/26/7289495/microbiome-gut-bacteria-health