(my description might be wrong) They start with a prediction; they modify mice and show that prediction is true; they then find human samples (staff and patients at an inpatient ED unit) and they find the staff don't have the particular gut flora while patients do. It's going to be really hard to get ethical approval to give the gut flora to healthy people - to give those people anorexia, so there is a missing step.
But for obesity it's not that hard.
Here's one for anorexia and bulemia. http://www.nature.com/tp/journal/v4/n10/full/tp201498a.html
(my description might be wrong) They start with a prediction; they modify mice and show that prediction is true; they then find human samples (staff and patients at an inpatient ED unit) and they find the staff don't have the particular gut flora while patients do. It's going to be really hard to get ethical approval to give the gut flora to healthy people - to give those people anorexia, so there is a missing step.