INS and Insulin resistance: However, HOMA-IR does not inform us about CNS insulin resistance or even CNS insulin levels because (1) the saturable nature of the BBB transporter means that the relation between blood and CNS levels of insulin are not linear, (2) the CNS is not part of the classic feedback loop controlling insulin release, and (3) as discussed in further detail below, the effect CNS insulin does have on peripheral insulin and glucose levels is opposite to that of peripheral insulin.