A method for screening for a foodstuff providing production of milk having an immunoregulatory action, a novel foodstuff having an immunoregulatory action, and a method for producing it are provided. A diet or substance that increases or decreases an amount of microRNA present in milk of a mammal is identified 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 to screen for a diet or a substance providing production of breast milk having an immunoregulatory action.
