Abstract: Breast milk is the best food for infants. It can not only provide comprehensive nutrients for infants, but also contribute to the healthy growth of infants due to its unique physiological characteristics. The osmolality of breast milk is usually 300 mOsm/kg H2O, which is not affected by race or lactation time. However, the osmolality of formula milk on the market is higher than that of breast milk. Hypertonic feeding has been considered to be related to a high incidence of gastroesophageal reflux (GER) and necrotizing enterocolitis (NEC) in infants (especially preterm infants) due to their immature gastrointestinal and renal systems. It is also considered to be not conducive to the healthy development of infant kidneys. In this paper, we systematically analyzes the clinical data of hyperosmotic feeding and infant GER, NEC and kidney health. The existing data show that hyperosmotic feeding could prolong the retention time of foods in the infant stomach, increase the chance of infant GER, increase the contents of microalbumin and retinol binding proteins as biomarkers for early glomeruli and renal tubule injury respectively, damaging infant kidney health; however, current data do not support a clear correlation between hyperosmotic feeding and NEC in infants. Besides, the article summarizes recent studies on the osmotic pressure of human milk and infant formula and the factors affecting it, presents some strategies for regulating the osmotic pressure of infant formula, and proposes future directions for the development of infant formula.

Key words: breast milk; osmotic pressure; infant; formula milk; health