Yes, it is theoretically possible. However, you would have to consume large amounts of certain foods. Realistically, however, this is only feasible for very few people. To ensure the intake of about 2 g, the daily dosage recommended by doctors, of omega-3 fatty acids per day, you would have to consume about 100 g of herring, 150 g of tuna, 250 g of salmon, 300 g of mackerel, 1.5 kg of trout or 3 kg of cod per day.