Some new research
has been published that supports this notion that gut bacteria are responsible for at least some obesity. What the authors did is described in the article, but the Cliff notes version is this: In both mice and humans, there is a difference in the gut bacteria of the lean and obese. After gastric bypass surgery, the gut bacteria changes to more closely match that of lean people. To see if that is a cause or effect of weight loss, the authors did gastric bypass surgery on some obese mice and the mice lost weight as expected. Then they transferred gut bacteria from those mice to other obese mice that didn't have the surgery and they too lost weight. Their conclusion is that weight loss after gastric bypass surgery is not due solely to the anatomical changes, but are also due to physiological changes induced by a change in gut bacteria.