Protein content: The protein content of mackerel is relatively high, with about 20g of protein per 100g of mackerel, while the protein content of sardines is about 14g. Protein is an important nutrient for human body to build tissues and maintain normal functions. ω-3 fatty acid content: mackerel is rich in ω-3 fatty acids, especially EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which is very important for cardiovascular and cerebrovascular health and nervous system development.