Major depressive disorder (MDD) is a leading cause of disability, and antidepressant drug treatment is only effective in over half of patients with a high prevalence of treatment resistance. The importance of nutrition in mental health is gaining recognition. Omega-3 is an essential polyunsaturated fatty acid (PUFA) vital for anti-inflammatory processes and brain integrity. In the absence of the body's ability to make Omega-3, it or its precursors must be acquired from the diet. Yet altered metabolic pathways can hamper the process and the adequate balance with PUFA Omega‐6 is also crucial, as elevated levels of Omega-6 are linked to several diseases. An extensive amount of research suggests that higher Omega-3 levels reduce the occurrence of depression. Yet results using just Omega-3s for depression have been varied. This European-wide study sought to investigate how the PUFA status could affect the clinical response to treatment with antidepressants. 60-adults with an average age of 41 with major depressive disorders received antidepressive treatment. Their red blood cell fatty acids content was determined, and at the end of the 8-week trial treatment responders and non-responders were identified. Findings affirmed the existing knowledge that depressive symptoms are strongly associated with PUFA status. Patients who did not respond to treatment showed low levels of Omega-3 and an unfavourable ratio of Omega-3 to Omega-6 at the start of treatment. Higher levels of Omega-3 fatty acid of DHA seemed to produce a better clinical response to treatments than the Omega-3 of EPA. The authors discussed some potential mechanisms and suggested that PUFA intake and metabolism could be a potential tool for the management of treatment-unresponsive patients with depression. This review highlights the clinical importance of considering PUFA status and metabolism in the support of major depressive disorders.