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Background: Nonalcoholic fatty liver disease (NAFLD) and insulin resistance are common in overweight adolescents. Objective: The purpose of this study was to determine the relation between NAFLD and insulin sensitivity in liver and skeletal muscle by studying overweight adolescents with a normal or high intrahepatic triglyceride (IHTG) content, who were matched for age, sex, body mass index (BMI; in kg/[m.sup.2]), and Tanner stage. Design: Stable-isotope-labeled tracer infusion and the hyperinsulinemic-euglycemic clamp procedure were used to assess skeletal muscle and hepatic insulin sensitivity, and magnetic resonance spectroscopy was used to assess the IHTG content in 10 overweight (BMI = 35.9 [+ or -] 1.3) adolescents with NAFLD (IHTG = 28.4 [+ or -] 3.4%) and 10 overweight (BMI = 36.6 [+ or -] 1.5) adolescents with a normal IHTG content (3.3 [+ or -] 0.5%). Results: The baseline plasma glucose concentration and the rate of appearance of glucose in plasma were the same in subjects with a normal (87.1 [+ or -] 1.2 mg/dL, 16.2 [+ or -] 1.1 [micro]mol x kg fat-free [mass.sup.-1] x [min.sup.-1]) or high (89.2 [+ or -] 2.5 mg/dL, 16.3 [+ or -] [micro]/xmol x kg fat-free [mass.sup.-1], [min.sup.-1]) IHTG content. However, compared with subjects who had a normal IHTG content, subjects with NAFLD had a lower hepatic insulin sensitivity index, based on baseline glucose kinetics and insulin concentrations (4.0 [+ or -] 0.5 compared with 2.4 [+ or -] 0.4; P < 0.05) and an impaired increase in glucose uptake during insulin infusion (169 [+ or -] 28.1% compared with 67 [+ or -] 9.6% above baseline; P < 0.01). In addition, the plasma triglyceride concentration was greater and the plasma HDL-cholesterol concentration was lower in subjects with NAFLD than in those with a normal IHTG content. Conclusion: An elevated IHTG content in overweight adolescents is associated with dyslipidemia and with insulin-resistant glucose metabolism in both liver and skeletal muscle.

Background: It is commonly believed that moderate aerobic exercise leads to changes in diet composition, specifically, an increase in carbohydrate intake at the expense of fat intake. Objective: The goal was to determine the effects of a supervised, long-term program of exercise on the macronutrient intake of previously sedentary, overweight and moderately obese men and women. Design: Participants (n = 74) were recruited from the university and surrounding communities and were randomly assigned to the exercise or control group. Exercise of moderate intensity was performed for 45 min/d, 5 d/wk, under supervision. Diet intake was ad libitum and was measured for energy and macronutrient composition at baseline and at 5 other occasions across the 16-mo study by use of weighing and measuring techniques. Each measurement consisted of a 2-wk period of direct measurement in the university cafeteria. Food consumption outside the cafeteria during the 2-wk periods (ie, snacks) was measured by multiple-pass 24-h dietary recall procedures. Results: There were no significant differences for men or women between the exercise and control groups from baseline to 16 mo in fat, carbohydrate, or protein intake expressed as grams or as percentages of total energy intake. Conclusion: Sixteen months of exercise of moderate intensity does not measurably alter the macronutrient intake of young adults. KEY WORDS: Long-term exercise, macronutrient intake, plate waste, energy intake, energy expenditure of exercise, obesity