LEPR and hyperinsulinemic hypoglycemia, familial, 4: In summary, we have presented evidence arguing against the requirement of the leptin system in the normalization of energy and glucose homeostasis associated with RYGB, which is consistent with the majority of previous studies in Zucker fatty fa/fa and Zucker diabetic fatty fa/fa rats as models of leptin receptor deficiency [61,62,63,66,67,69,72,76,79,81] and thus places them in a new light.