Aminotransferase activity in morbid and uncomplicated obesity: Predictive role of fasting insulin

Background and aims.: An elevation in liver enzymes and, most notably, high serum alanine aminotransferase (ALT) activity, has been correlated with metabolic syndrome and obesity. However, whether obesity per se or obesity-related co-morbidities affect aminotransferase activity is still unclear. In this study we sought to evaluate serum aminotransferase activity in morbid and uncomplicated obese subjects. Methods.: In this cross-sectional study, serum aminotransferase activity, anthropometric and metabolic parameters were assessed in 290 morbid and 105 uncomplicated consecutive obese subjects matched for body mass index (BMI) (40.1 ± 6.8 vs. 39.9 ± 8.3 kg/m², respectively), age (35.9 ± 10 vs. 34.8 ± 9.6 years, respectively), sex distribution and duration of obesity. Results.: Uncomplicated obese subjects showed significantly lower serum ALT activity (17.58 ± 6.3 (range 10-39) vs. 23.43 ± 16 (range 12-89) U/l, (p < 0.001)), and lower aspartate aminotransferase (AST), AST/ALT ratios and gamma-glutamyltranspeptidase (γGT) (p < 0.01 for all) than morbid obese subjects. Only 11% women and 19% men in the uncomplicated obese group showed high ALT levels, while ALT activity was high in 48% women and 51% men in the morbid obese group. Fasting insulin was the best correlate of ALT activity (R² = 0.21, p = 0.003). Conclusions.: Our findings show that elevated ALT and AST activity are associated with increased fasting insulin and not with obesity per se, suggesting that the presence of insulin resistance, rather than BMI alone, plays a role in mediating the increased aminotransferase activity.