Adaptation of feeding to a low fat yield in breast milk.

The effect of a low milk fat yield was assessed in a blinded prospective study of healthy term infants and mothers encouraged to breast-feed. Fat yield index was calculated as milk volume collected by Egnell pump multiplied by the "creamatocrit." Two weeks after delivery mothers who had a relatively low fat yield index (less than or equal to 30th percentile) were matched with mothers with a higher fat yield index and with formula-feeding mothers. Between 2 and 6 weeks the low fat yield group had a marginally lower weight gain but similar growth in length and head circumference to that of the higher fat yield group. The low fat yield group spent more time per feeding and had more complete breast emptying, resulting in a fat yield index comparable with the higher fat yield group for the mean milk volume ingested by the infant at 6 weeks. A low fat yield had no adverse effect on maternal satisfaction or maternal-infant interaction during feeding. Formula feeders spent the least time in feeding and en face gazing. Adaptation of breast-feeding to a low fat yield sustains infant intake and growth, maternal-infant interaction, and maternal satisfaction. However, there is little reserve if milk production diminishes. Further study is needed to define the limits of adaptation and effective interventions if fat yield is inadequate.