Breast milk
Casein that is heat-treated has been shown to be more allergenic and harder to digest when fed to infants. Minimally-processed infant formula can be used in place of traditional formulas, as well as alternative formulas, if breastfeeding is not available. Breast milk has not typically been shown to cause an allergic reaction, but should be administered to an infant with caution each time in case of adverse reaction from something the breastfeeding parent consumed that contained casein. Following a casein-free diet has been shown to improve outcomes of infants who are breastfed while allergic or intolerant to dairy protein. Human breast milk has been proven to be the best food for an infant, and should be tried first where available.