It is already known that ω3 polyunsaturated fatty acids (PUFAs), abundant in fish, have anti-atherosclerotic and lipid metabolism improving effects. In the past two decades, their preventive effects on mood disorders and symptom improvement effects have also been reported. However, in Japan, meat intake surpassed seafood intake for the first time in 2006, and the gap continues to widen, with young people, in particular, showing a marked tendency to eat less fish. We have previously conducted a cross-sectional study with approximately 4,000 university students and found that the risk of depression was lower among students with high fish consumption. Pregnant women need to consume more ω3 PUFAs than usual for the formation of the fetus, and animal experiments have reported that if they do not consume enough ω3 PUFAs during this period, they may sacrifice the ω3 PUFAs in their brain to supply their fetus. We conducted a longitudinal study of 80,000 pregnant women and found a negative association between fish consumption and the risk of postpartum depression. In this presentation, we will further introduce epidemiological and intervention studies reported from around the world and discuss the importance of ω3 PUFAs in mental health.