Background. Obesity is associated with insulin resistance, which is the main pathogenic factor for nonalcoholic fatty liver disease (NAFLD). NAFLD can progress without associated elevations in liver enzymes. Therefore, we investigated the effects of weight loss on normal transaminase levels in obese subjects who are at risk for NAFLD. Methods: Thirty-seven obese patients with normal ALT levels were evaluated. All patients received an individualized low-calorie diet over at least 6 months. Twenty-two patients who achieved weight loss of at least 5% body weight were identified as the study group and the others as the control group. Transaminases, insulin resistance, and body mass index were compared before and after the intervention. Results: Hepatic steatosis was found in 83.8% of obese patients. ALT was correlated with HOMA-IR in all patients at baseline (r = 0.363, P = 0.027). At the end of the follow-up, mean weight loss achieved in the study and control groups were 9.2% (8.7 +/- 3.0 kg) and 0.3% (0.5 +/- 2.8 kg), respectively. In the study group, HOMA-IR and ALT decreased from 4.0 +/- 1.8 to 2.4 +/- 0.9 and from 21.4 +/- 6.6 IU/L to 16.8 +/- 5.5 IU/L, respectively (P = 0.005 and P = 0.044). Conclusions: The results demonstrate that weight loss results in a decrease in normal ALT levels as well as insulin resistance. Therefore, the normal range for ALT may need to be reassessed.