IRS

1. Metabolic flexibility V V V II II II III III III IV IV IV I I I V II III IV I Metabolic inflexibility Hyperinsulinemia Fasting X Hyperinsulinemia Fasting a. c. Glucose IR IR GLUT GLUT IRS IRS DAG Ceramides DAG Ceramides Pyruvate Acyl-CoA Acyl-CoA Acyl-CoA FFA β oxidation TCA β oxidation TCA TG fATP fATP Insulin-sensitive Glucose Glucose IR IR b. GLUT d. GLUT IRS IRS Pyruvate FFA FFA Pyruvate X TCA β oxidation TG TG X TCA β oxidation fATP fATP Insulin-resistant

2. Figure S1. Cellular processes in insulin-responsive tissues. a. In the fasting state, glucose uptake into insulin-responsive tissues decreases and fuel selection switches from glucose to lipid oxidation (metabolic flexibility). Substrate availability and energy demand are low. b. Theinsulin-resistant state is characterized by the inability to adapt ATP synthetic rates (fATP) to substrate availability; lipid oxidation rates are, therefore, not increased adequately. Lipid metabolites (Acyl-CoA, DAG, ceramides) increase and TG accumulate. Mitochondrial plasticity, for example metabolic flexibility, is the limiting factor for in vivo ATP synthetic rates in insulin-resistant humans. c. During hyperinsulinemia, glucose uptake increases in insulin-responsive tissues, fuel selection switches from lipid to glucose oxidation (metabolic flexibility). In the insulin-stimulated state, energy demand is high and ATP synthetic flux rate is increased. d. In the insulin-resistant state, glucose transport and phosphorylation is reduced and lipid oxidation rates are not decreased adequately. DAG and ceramides induce insulin resistance. Abbreviations: DAG, diacylglycerol; FFA, free fatty acids; GLUT, glucose transporter; IR, insulin receptor IRS, insulin receptor substrate; TCA, tricarboxylic acid cycle; TG, triglycerides.