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Gender-Related Differences in the Metabolic Response to Fasting

Departments of Endocrinology and Metabolism (M.R.S., H.P.S., E.F., M.J.S.), Medical Biochemistry (J.E.G., J.M.A.), and Clinical Chemistry (M.T.A.), Laboratory of Endocrinology, Academic Medical Center, University of Amsterdam, 1100 DD Amsterdam, The Netherlands; and Department of Molecular Genetics (J.F.C.G.), Maastricht University, 6200 MD Maastricht, The Netherlands

Address all correspondence and requests for reprints to: M. R. Soeters, M.D., Department of Endocrinology and Metabolism, Academic Medical Center, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands. E-mail: m.r.soeters{at}amc.uva.nl.

Context: Free fatty acids (FFA) may induce insulin resistance via synthesis of intramyocellular ceramide. During fasting, women have lower plasma glucose levels than men despite higher plasma FFA, suggesting protection from FFA-induced insulin resistance.

Objective: We studied whether the relative protection from FFA-induced insulin resistance during fasting in women is associated with lower muscle ceramide concentrations compared with men.

Main Outcome Measures and Design: After a 38-h fast, measurements of glucose and lipid fluxes and muscle ceramide and fatty acid translocase/CD36 were performed before and after a hyperinsulinemic euglycemic clamp.

Results: Plasma glucose levels were significantly lower in women than men with a trend for a lower endogenous glucose production in women, whereas FFA and lipolysis were significantly higher. Insulin-mediated peripheral glucose uptake was not different between sexes. There was no gender difference in muscle ceramide in the basal state, and ceramide did not correlate with peripheral glucose uptake. Muscle fatty acid translocase/CD36 was not different between sexes in the basal state and during the clamp.

Conclusion: After 38 h of fasting, plasma FFA were higher and plasma glucose was lower in women compared with men. The higher plasma FFA did not result in differences in peripheral insulin sensitivity, possibly because of similar muscle ceramide and fatty acid translocase/CD36 levels in men and women. We suggest that during fasting, women are relatively protected from FFA-induced insulin resistance by preventing myocellular accumulation of ceramide.