Scientists have found a form of bacteria found in large doses in obese people and not in skinny people. Right now it is not totally proven if the bacteria causes fatness or if fatness causes more of the bacteria to grow. The bacteria Firmicutes may cause infectobesity. In future the newest diet pills may kill specific bacteria that causes fat gain & adding good bacteria that causes fat loss.
Tests on Mice show when they are loaded with bacteria called Firmicutes and low in another bacteria called Bacteroidetes they get twice as fat as other Mice on the same diet.
Common sense dictates that having the right kind of bacteria will make you healthier. You can do this already by picking up a good Pro-biotic that can withstand room temperatures. Many pro-biotics that need to be refrigerated have already died before they even get to the store shelves.
http://microbioresearch.blogspot.com/2008/07/overweight-blame-bacteria-in-your-gut.html