A Mediterranean-style dietary intervention supplemented with fish oil improves diet quality and mental health in people with depression: A randomized controlled trial (HELFIMED)

Randomized controlled trial in community-recruited adults aged 18 to 65 years with self-reported or diagnosed depression in Australia. Participants were assigned to the Mediterranean-style diet plus fish oil intervention or a social-group comparator, with assessments at baseline, 3 months, and 6 months.

Participants in the active arm received a Mediterranean-style dietary intervention supplemented with fish oil capsules for 6 months. The fish oil dose was 2 capsules per day, with each EPAX 1050 TB capsule containing 450 mg DHA and 100 mg EPA; capsules were supplied at baseline and again at 3 months to cover the full intervention period. The program also included food hampers with Mediterranean-style foods and fortnightly group sessions during the first 3 months.

The Mediterranean-style diet plus fish oil intervention produced greater improvements in depression and mental health-related quality of life than the social control, and these gains were maintained at 6 months. Depression improved more in the active arm than in the social group at 3 months (between-group estimate -4.52, P = 0.027, 95% CI -8.53 to -0.52), and depression scores improved by 45% versus 26.8% in the social group. Mental health-related quality of life also improved, including AQoL happiness (estimate 0.06, P = 0.037), and dietary improvements were seen in Mediterranean diet score, vegetables, fruit, nuts, legumes, and wholegrains with lower unhealthy snacks and meat/chicken intake. Benefits were associated with healthier dietary changes and changes in erythrocyte omega-3 and omega-6 PUFA levels.

The intervention combined dietary change with fish oil, so the contribution of each component cannot be isolated. The comparator was a social-group condition rather than an inert placebo, which may have contributed to improvement through social contact. Attrition was notable, with retention to 3 months at 72% and to 6 months at 63% in the MedDiet group, and the study was relatively small and conducted at a single site.