A systematic review of six placebo controlled RCTs reported that fecal microbiota transplantations (FMT) from lean donors into adults with obesity show no improvement of parameters including hepatic insulin sensitivity, BMI, fasting plasma glucose, or cholesterol level, other than a reduction of HbA1c levels at six weeks post-FMT (129). The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.