DEGREE OF BREAST EMPTYING EXPLAINS CHANGES IN THE FAT-CONTENT, BUT NOT FATTY-ACID COMPOSITION, OF HUMAN-MILK

We compared within.and between breastfeed changes in milk fat to short -term rates of milk synthesis and degree of breast emptying (measured using the Computerized Breast Measurement system) over two 24 h period s for five lactating mothers. The fat content (f) of fore and hind mil k samples increased more steeply as the breast was progressively empti ed by the infant (degree of emptying, d, range 0-1;f = 21.59+9.38d+70. 99d2; P < 0.0001; r2 = 0.68; n = 154). For the nine individual breasts , between 41-95% of the variance of the fat content of milk was explai ned by degree of breast emptying. We argue that this relationship expl ains differences in the circadian rhythm of the fat content of milk an d allows the accurate calculation of the average fat content of milk c onsumed by infants (37-66 g/l for the nine individual breasts). The fa tty acid composition of the fore and hind milk samples was determined for four of the mothers. We observed within and between breastfeed var iability in the relative proportions of the seven major fatty acids of milk fat and these changes are discussed with reference to the contro l of fat synthesis in the human mammary gland.