In the first study, Yu and co-workers (2020) evaluated in a small group of adult patients with obesity and mild-moderate insulin resistance (~70% females) the effect of a weekly administration for six weeks of FMT capsules containing fecal microbiota derived from a healthy lean donor.; despite successful variable engraftment into the recipient’s microflora, the authors did not observe any significant metabolic improvements in terms of either insulin sensitivity or body composition [159]. This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.