Breastmilk cell and fat contents respond similarly to removal of breastmilk by the infant

Abstract

Large inter- and intra-individual variations exist in breastmilk composition, yet factors associated with these variations in the short-term are not well understood. In this study, the effects of breastfeeding on breastmilk cellular and biochemical content were examined. Serial breastmilk samples (∼5 mL) were collected from both breasts of breastfeeding women before and immediately after the first morning breastfeed, and then at 30-minute intervals for up to 3 hours post-feed on 2-4 mornings per participant. The infant fed from one breast only at each feed. Effects of pump versus hand expression for samples were evaluated. A consistent response pattern of breastmilk cell and fat contents to breastmilk removal was observed. Maximum fat and cell levels were obtained 30 minutes post-feed (P<0.01), with up to 8-fold increase in fat and 12-fold increase in cell content compared to the pre-feed values, and then they gradually decreased. Breastmilk cell viability and protein concentration did not change with feeding (P>0.05), although large intra-individual variability was noted for protein. Expression mode for samples did not influence breastmilk composition (P>0.05). It is concluded that breastmilk fat content, and thus breast fullness, is closely associated with breastmilk cell content. This will now form the basis for standardization of sampling protocols in lactation studies and investigation of the mechanisms of milk synthesis and cell movement into breastmilk. Moreover, these findings generate new avenues for clinical interventions exploring growth and survival benefits conferred to preterm infants by providing the highest in fat and cells milk obtained at 30 min post-expression.

Figure 1. Responses of milk fat, cellular and protein contents and cell viability to feeding in the feeding and non-feeding (control) breasts.

(A) Inter- and intra-individual variation in responses to feeding. Each line represents a feed, and all feeds from all participants are shown. (B) Distribution of values from all feeds and participants (N = 6) for the feeding (N = 20) and non-feeding (N = 16) breasts at each time point. Pre: immediately pre-feed collection; post: immediately post-feed collection. Boxes show first and third quartiles; horizontal bars within boxes indicate median values; and ‘whiskers’ plus outlier dots show the range of values.

Figure 2. Relationship between milk fat and cell contents in all the participants for all the feeds and repeats (N = 36).

Lines indicate different sampling points, showing a consistent pattern over time. Different colors indicate different sampling time points. Cell content was strongly and linearly related to fat content (P<0.001), after accounting for the effect of time.

Figure 3. Percentage increase in the measured fat, cell and protein contents, and cell viability relative to the starting pre-feed values, calculated as (measured value – pre-feed value)/pre-feed value) ×100.

Note that towards the end of the feed this can be negative, when the measured value goes below the pre-feed value. Pre: immediately pre-feed collection; post: immediately post-feed collection.

Figure 4. Comparison of pre-feed values between the feeding and the non-feeding (control) breasts for milk fat, cell and protein contents, and cell viability among participants and different feeds.

(A) Direct comparison within each feed. (B) Distribution of pre-feed values for each variable and each breast.

Figure 5. Inter- and intra-individual variation in milk fat, cell and protein contents and cell viability recorded.

Variation between feeds and breasts within and among individuals. Values for control (non-feeding) and feeding breasts are on the left and right sides of the plots, respectively.

Figure 6. Effects of expression mode (hand versus pump expression) on milk fat, cell and protein contents, and cell viability for the feeding breast (N = 20 for cells and cell viability; N = 19 for fat; N = 18 for protein).

Pre: immediately pre-feed collection; post: immediately post-feed collection.