Disclosed is a method for screening for a diet or a substance providing production of breast milk having an immunoregulatory action, which comprises identifying a diet or a substance that increases or decreases amount of microRNA present in milk of a mammal, excluding a human, by using correlation of microRNA profiles in the milk and a diet ingested by the mammal or a substance contained in the diet as an index, wherein the immunoregulatory action is an immunostimulating action, and when the amount of the microRNA increases, it is judged that the diet or substance provides production of breast milk having an immunostimulating action and wherein the immunoregulatory action is an immunosuppressive action, and when the amount of the microRNA decreases, it is judged that the diet or substance provides production of breast milk having an immunosuppressive action.
