Characteristics of Normal Weight Insulin-Resistant Adults with Unfavorable Health Outcomes.

Background: Insulin resistance can be present in otherwise healthy, normal weight adults. Whether there are phenotype/sex-differences between normal weight insulin-resistant (NWIR) and normal weight insulin-sensitive (NWIS) Caucasians and whether there are differences in adverse health outcomes are unknown. Our goal was to define phenotypes and intermediate-term health outcomes of NWIR versus NWIS Caucasian adults. Methods: We analyzed data from 227 healthy volunteers body mass index 18 to <25.0 kg/m² who underwent insulin clamp studies between January 1987 and January 2017 at Mayo Clinic to identify those in the top (NWIS, n = 56) and bottom (NWIR, n = 56) quartiles of insulin action. We compared the phenotypical characteristics and were able to collect medical records data for 80% of NWIS and 88% of NWIR to identify time to onset of hypertension, hyperglycemia, coronary heart disease, cerebrovascular disease, peripheral vascular disease, and all cause death; the follow-up averaged 11 (4, 20) years. Results: Body fat was significantly greater and peak VO₂ was significantly less in both NWIS than NWIR males and females. Only in females was abdominal subcutaneous fat by computed tomography significantly greater in NWIR than NWIS. In NWIR males high-density lipoprotein-cholesterol and fat free mass were significantly less, and fasting insulin was greater than NWIS males. For the entire NWIS population, Kaplan-Meier disease-free survival analysis showed longer times free of hypertension, hyperglycemia, and some cardiovascular diseases than for NWIR. Conclusions: There are sex-specific phenotypes of NWIR in Caucasian adults. NWIR may be associated with accelerated onset of some adverse medical outcomes.