A recent small study, Effects of Fecal Microbiota Transplantation With Oral Capsules in Obese Patients, found results that to me at least, seemed wholly unsurprising. 22 patients with obesity were randomly assigned to receive either a "fecal microbiota transplantation" from a donor whose BMI was 17.5 or a placebo and to take them for 3 months (and for those curious, the induction dose was 30 capsules).
The transplants were successful in changing the microbiome of the recipients, but alas, did not affect their weights.
Perhaps the only thing surprising about all of this is that there are people out there who strongly believe that a microbiome transplant stands a chance against thousands of genes, dozens of hormones, and a Willy Wonkian food environment all of which being coupled with millions of years of an evolutionary crucible of extreme dietary insecurity.