Few studies, with inconsistent results, have been conducted to examine the effect of protein and amino acid consumption on non-alcoholic fatty liver disease (NAFLD). Therefore, this study aimed to assess the relationship between dietary intake of amino acids or groups of amino acids and the risk of NAFLD.

 This case-control study included 171 participants with NAFLD and 730 controls from Tehran, Iran. A validated Food frequency questionnaire (FFQ) with 168 items, was used to evaluate dietary information. Odds ratios (ORs) and corresponding confidence intervals (CIs) were calculated by regression models, adjusted for potential confounders including age, sex, body mass index (BMI), smoking status, physical activity, history of diabetes mellitus, and total energy intake.

 The mean ± standard deviation (SD) age of participants was 43.26 ± 13.9 years. Intake of total protein and all amino acids was significantly higher in patients with NAFLD than in the control group (P < 0.001). Increased risk of developing NAFLD compared to the reference quartile was observed in the highest quartiles of dietary isoleucine (OR, 4.72; 95%CI, 1.57-14.19), tyrosine (OR, 5.11, 95%CI, 1.73-15.05), threonine (OR, 3.47; 95%CI, 1.16-10.33), and valine (OR, 4.51; 95%CI, 1.45-14.02) intake. Subgroup analysis by sex revealed that in the females, the OR for NAFLD were 0.36 (95%CI, 0.13-0.98) among those with the highest intake of non-essential amino acids, and 2.78 (95%CI, 1.02-7.50) among those with the highest intake of essential amino acids compared to those in the first quartile. However, there was no significant trend among male cases.