Dietary interventions for weight loss are effective therapies for nonalcoholic fatty liver disease (NAFLD). The Mediterranean diet might benefit these patients, but it is not followed consistently in Northern European countries. We examined factors that determine Mediterranean diet adoption and maintenance in a northern European population. METHODS:We used a mixed-methods approach to investigate the effects of a 12-week Mediterranean diet intervention and perceived barriers and facilitators. Nineteen adults with NAFLD were recruited from a tertiary hepatology center in England. Participants were taught behavioral strategies through the provision of shopping lists, meal planners, and recipes; no advice was given on calorie allowances or physical activities. We used the 14-point Mediterranean diet assessment tool to assess dietary intake, based on a small number of foods in servings per day or servings per week, at baseline and after 12 weeks; participants were assigned scores of low (<5 points), moderate (6-9 points), or high (10-14 points). Semistructured interviews were audiorecorded, transcribed, and analyzed using the framework method. RESULTS:Twelve weeks after the dietary advice, Mediterranean diet adoption significantly increased from moderate to high (mean increase, 2.2 points; from 7.6 -2.5 at baseline to 9.8 -2.8 at 12 wk) (P [ .006). This increase was associated with a mean reduction in body weight of 2.4 kg (from 99.2 -17.0 kg at baseline to 96.8 -17.5 kg at 12 wk) (P [ .001) and increased serum concentrations of high-density lipoprotein cholesterol in 72% of participants (from 1.10 -0.8 at baseline to 1.20 -1.30 vs 1.00 -0.5 at 12 wk) (P [ .009). Increased nutrition knowledge and skills, family support, Mediterranean diet promotion in media and clinical settings, and nutritional care facilitated diet changes. Barriers to Mediterranean diet uptake included an obesogenic environment, life stressors, and demand for convenience. Poor understanding of the causes and significance of NAFLD adversely affected readiness to change dietary habits. CONCLUSIONS:In an analysis of patients with NAFLD in the northern United Kingdom, we found a 12-week Mediterranean diet intervention was acceptable and associated with significant reductions in body weight and increased serum levels of high-density lipoprotein. We identified barriers and facilitators that could support appropriate treatment adaptations and guide personalized intervention approaches.