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Aim: To assess a relationship between longitudinal changes in liver fat content and biochemical parameters in obese children after 1-year nutritional intervention., Methods: Forty-six obese children, 21 males and 25 females, aged 6-14 years, underwent metabolic measurements, liver ultrasonography (US) and chemical-shift magnetic resonance imaging (MRI) examinations at baseline and after 1-year nutritional intervention. A child was defined obese if her/his body mass index (BMI) was above the age- and sex-adjusted BMI Cole's curve passing through the cut-off of 30 kg/m(2) at 18 years. BMI Z scores were calculated and adjusted for age and gender by using the Cole's LMS-method and Italian reference data. Biochemistry included serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Abdominal US and chemical-shift MRI were performed according to a randomized sequence. The same radiologist performed US by a GE Logiq 9 (General Electric Healthcare Medical Systems, Milwaukee, WI, United States) using a 3.5-MHz convex array transducer. Liver echogenicity was evaluated independently on videotape by 3 radiologists unaware of the child and MRI outcomes, and a consensus was established. Another experienced radiologist, unaware of the child and US data, performed the abdominal chemical-shift MRI with a 1-t system NT-Intera (Philips Medical Systems, Best, The Netherlands) and a phased-array coil. Liver fat fraction (FF) on MRI was judged elevated when greater than 9%. A FF > 18% was considered expressing more severe cases of fatty liver according to Fishbein. A nutritional-behavioral intervention was recommended to promote a normocaloric balanced diet and active lifestyle based on the Italian guidelines for treatment of childhood obesity., Results: Compared to baseline, at the end of intervention children showed lower intakes of energy (mean ± SD: 2549 ± 1238 Kcal vs 1770 ± 622 Kcal, P < 0.0001), total fat (90 ± 47 g vs 52 ± 23 g, P < 0.0001), carbohydrates (356 ± 174 g vs 241 ± 111 g, P = 0.001), and protein (99 ± 48 g vs 75 ± 23 g, P = 0.006) intakes. Prevalence of FF ≥ 9% declined from 34.8% to 8.7% (P < 0.01), with a mean reduction of 7.8% (95%CI: 5.0-10.6). At baseline, FF was associated with liver biochemical parameters (maximum P < 0.001). At the end of the intervention association was found with AST (P = 0.017). Change of FF was associated with change in AST (P = 0.027) and ALT (P = 0.024). Rate of increased liver echogenicity declined from 45.6% to 21.7% (P < 0.0001). Liver echogenicity was associated with ALT at baseline only (P < 0.001). An age- and sex- adjusted multiple regression analysis showed that FF change was independently associated with change in serum AST (adjusted regression coefficient 0.348, P = 0.048)., Conclusion: The results suggest that in obese children longitudinal changes in liver fat content based on MRI may be associated with change in serum transaminases suggesting novelty in monitoring nonalcoholic fatty liver disease.