Extent of Unidentified Complaints and Depression Is Inversely Associated with Fish and Shellfish Intake in Young Japanese Women

<b>Background/Objectives</b>: Vague physical complaints with no corresponding organic disease background are called unidentified complaints. The symptoms of patients with unidentified complaints closely resemble medically unexplained or persistent physical symptoms, with the onset sometimes masked by mental disorders. Over the past 50 years, numerous studies have connected unfavorable eating habits to these symptoms; however, no study has systematically examined the association between the symptoms and specific nutrients or food items. <b>Methods</b>: We conducted a cross-sectional study of young Japanese women, using questionnaire surveys, to assess their nutritional intake, quantify unidentified complaints and depression, and identify nutrients/food items primarily associated with the severity of these conditions. <b>Results</b>: Our findings indicate that participants with high scores for unidentified complaints, depression, or both had lower intake levels of eicosapentaenoic acid, docosahexaenoic acid, vitamin D, and vitamin B₁₂ than those with low scores, alongside reduced fish and shellfish consumption. Notably, the median fish and shellfish intake in the group with high scores for both unidentified complaints and depression was less than one-fourth of that in the low-score group. <b>Conclusions</b>: The results align with previous findings, demonstrating a modest inverse association between fish intake and depression risk, and suggesting the involvement of fish and shellfish intake in the occurrence of unidentified complaints.