Non-esterified fatty acids do not contribute to insulin resistance in persons at increased risk of developing Type 2 (non-insulin-dependent) diabetes mellitus

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Abstract
The mechanisms underlying insulin resistance in Type 2 (non-insulin-dependent) diabetes mellitus are not fully understood. An enhanced lipid/non-esterified fatty acid oxidation could provide an explanation. To test this hypothesis we examined the relationship between glucose and lipid metabolism in 44 first-degree relatives (28 glucose-tolerant and 16 glucose-intolerant) of Type 2 diabetic patients and in 18 healthy control subjects. Total body glucose disposal was impaired among both glucose-tolerant and glucose-intolerant relatives compared with control subjects (36.3±3.8 and 30.4±2.7 vs 47.7±3.4 μmol · kgLBM/s-1· min−1; p < 0.05). The impairment in glucose disposal among the relatives was primarily accounted for by impaired non-oxidative glucose metabolism (14.8±3.0 and 12.5±1.8 vs 25.3±3.1 μmol · kgLBM−1 · min−1; p −1· min−1). Furthermore, insulin suppressed lipid oxidation to the same degree in glucose-tolerant, glucose-intolerant relatives and control subjects (0.65±0.13, 0.88±0.15 and 0.59±0.09μmol · kgLBM−1 · min−1). An inverse correlation between plasma non-esterified fatty acid concentration and total body glucose disposal was observed in the group of control subjects (r=−0.540; pr=0.002; p=N.S.). In conclusion the present data challenge the view that the “glucose-fatty acid cycle” contributes to the insulin resistance seen in first-degree relatives of patients with Type 2 diabetes.