Translational Psychiatry - Antipsychotics and the gut microbiome: olanzapine-induced metabolic dysfunction is attenuated by antibiotic administration in the rat

Here is the work that shows that microbiota are involved in making you fat while on olanzapine and induce metabolic syndrome----initially there is an increase in eating during the first couple of weeks but then it levels off. Adding antibiotics to wipe out gut bacteria reduces the weight gain even though the rats are eating at equivalent levels. Problem is wiping out gut microbiota with antibiotics also increases weight relative to controls so it's not a good treatment strategy.

It's also already known that you can give two mice with different microbiota the same caloric intake and one will get fat and the other will remain thin just based on microbiota each is colonized with, you can also transfer the microbiota of a fat mouse to a thin and make them get fat.