Background & Aims: This RCT aimed to investigate the safety and efficacy of MF4637, a medical food comprising highly concentrated, highly purified, long chain (LC) omega-3 fatty acids, (460 mg eicosapentaenoic acid (EPA) and 380 mg docosahexaenoic acid (DHA)) in correcting the omega-3 fatty acid nutritional deficiency present in non-alcoholic fatty liver disease (NAFLD). The potential for MF4637 to reduce liver fat was evaluated in a subset of patients. Methods: 176 subjects with NAFLD were randomised to receive 3 g/d of LC-omega-3 fatty acids (n=87) or placebo (olive oil; n=89) for 24 weeks, in addition to following standard-of-care dietary guidelines for these patients. Thus, interventions were given on top of the dietary advice. The omega-3 index, omega-6:omega-3 fatty acid ratio (primary outcome) and quantitative measurements of red blood cell (RBC) EPA and DHA (secondary outcome) were determined at baseline and study completion. Magnetic resonance imaging-proton density fat fraction (MRI-PDFF) assessment of change in liver fat fraction was conducted in a subset of patients. Results: Of the 176 randomised subjects, 167 were analysed for the primary and secondary outcomes (n=81 in the MF4637 group; n=86 in the placebo group). Supplementation with MF4637 for 24 weeks significantly increased the omega-3 index and absolute values of RBC EPA and DHA, and decreased the omega-6:omega-3 fatty acid ratio in NAFLD patients compared to placebo (p<0.0001). There was a statistically significant reduction in liver fat content within both groups with no difference between them. An inverse relationship between change in absolute RBC EPA+DHA and change in liver fat, AST and ALT levels was seen suggesting that a greater increase in omega-3 content was associated with a reduction for both liver fat content and improvement in liver enzyme levels. Additionally, a significant liver fat-lowering effect of MF4637 compared to placebo was demonstrated in a subset of patients with baseline fatty liver index (FLI) score ≥ 40. There were no serious adverse events related to study interventions. Conclusions: The study results demonstrate that the medical food MF4637, was able to correct the nutritional deficiency of omega-3 in NAFLD patients above and beyond that obtained with nutritional counselling. This demonstrates that MF4637 is beneficial in raising the low omega-3 index observed in these patients. A reduction in hepatic steatosis was demonstrated with both intervention groups although no distinction between groups was seen. Further analyses demonstrate the potential to identify omega-3 sensitive patients using an easily available clinical tool for steatosis prediction.