NEW STUDY:  A novel study involving mice and humans, which is part of a growing fascination with gut bacteria and their role in health and diseases like IBS and Crohn’s disease, shows that gut bacteria could be linked to obesity.  Researchers found pairs of human twins in which one was obese and the other was thin.  They transferred gut bacteria from these twins into mice and watched what happened.  The mice with bacteria from fat twins grew fat; those that got bacteria from thin twins stayed lean.  However, Dr. Jeffrey I. Gordon of Washington University in St. Louis, the senior investigator for the study, says to use caution.  He says that they need to figure out which bacteria are responsible for the effect so that people can be given pure mixtures of bacteria instead of feces.  The part of the study that was the most shocking to other experts was an experiment indicating that, with the right diet, it might be possible to change the bacteria in a fat person’s gut so that they promote leanness rather than obesity. Researchers found that given a chance, bacteria from a lean twin will take over the gut of a mouse that already had bacteria from a fat twin.  The fat mouse then loses weight.  However, the opposite does not happen.  (