This UK based study was a systematic review and a meta-analysis of randomized trials. The search included large databases (e.g. Central, Medline, and EMBASE), trial registers, omega-3, and ongoing trials. Trials of adults with or without depression or anxiety, randomized to increased omega-3, omega-6 or total polyunsaturated fat for ≥ 24 weeks, excluding multifactorial interventions were reviewed. The authors of these studies were contacted if questions arose. The primary outcomes were as follows: 1) risk of depression or anxiety symptoms assessed by formal diagnosis or an appropriate scale, dichotomized to give risk of depression or anxiety in participants without depression or anxiety at baseline. 2) severity of depression and anxiety as a continuous scale in participants with or without anxiety and depression. 3) relapse in those with depression at baseline. This study used random-effects meta-analysis, sensitivity analyses, and subgrouping and Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) assessment.