I think the take home here from the above trials is that the hype far, far exceeded the evidence - if microbiota modulation for obesity was a drug requiring substantial financial investment, it very likely would have been dropped in preclinical development, and it certainly would have been dropped after these negative pilot trials. By contrast, the effect of, say FMT on single and multiple recurring C diff is very obvious, and the RCT evidence for an effect in ulcerative colitis is at least mixed, if not somewhat promising.

The reason for the focus on obesity, rather than say obesity-associated CVD or CKD or NAFLD or extra-GI cancers, is that these conditions take years to develop, in a relatively small number of people - it should be much easier to see an effect on weight in people already obese, if one exists. There is some very limited evidence that microbiota intervention can improve glucose homeostasis in people, but I wouldn’t hang my hat on those studies.