OBJECTIVES: The effect of light-to-moderate alcohol consumption (LMAC) in nonalcoholic fatty liver disease (NAFLD) remains a controversial subject. The aim of this study was to evaluate the relationship between LMAC and the severity of NAFLD in morbidly obese patients. METHODS: We studied 132 patients undergoing liver biopsy during bariatric surgery. The patients were divided into three groups: G1: alcohol intake greater than 20 g/day and less than 40 g/day; G2: alcohol intake less than 20 g/day; G3: no alcohol intake. Insulin resistance was defined by the Homeostasis Model Assessment (>3). NAFLD was classified according to the Matteoni types: type I: steatosis alone; type II: steatosis with inflammation; types III-IV: steatosis with ballooning and/or fibrosis. RESULTS: The mean age was 37.3+/-11 years. Sixty-three percent were females and body mass index was 43.9+/-5.6 kg/m. G1, G2, and G3 included 19, 56, and 57 patients, respectively. Histological diagnoses classified by levels of alcohol were: G1: 10.5% normal liver, 89.5% type III or IV; G2: 10.7% normal liver, 1.8% type I or II, and 87.5% grade III or IV; G3: 10.5% normal liver, 3.5% type I or II, and 86% type III or IV (one had cirrhosis). The presence of IR was similar in moderate and no alcohol consumption (81.3 and 78.7%) but significantly less in the light consumption group (54%, P<0.05). CONCLUSION: The results suggest that LMAC may have a protection effect against IR in severely obese patients. However, it had no impact on the severity of activity and stage of liver disease.