A 4-day test weighing study to assess volume and variations in fat and energy content of breast milk

Abstract

Background: Exclusive breastfeeding is recommended for the first six months of life. Breast milk intake and composition not only vary between populations and individuals, but also within feeds, within days and between days. Very limited information is currently available on the breast milk intake of exclusively breastfed infants, as well as on the energy and fat composition of breast milk from lactating women in South African. Aim: The aim of this study was to assess breast milk intakes, as well as energy and fat concentration of breast milk in a convenience sample of exclusively breastfed infants and their mothers from Potchefstroom in South Africa. Furthermore, the study determined within-feed, diurnal and between-day variations in energy and fat concentration of breast milk. Methodology: Twenty-four healthy mothers and their exclusively breastfed two to five-month old infants were recruited to stay at the metabolic unit of the North-West University in South Africa for a period of five days. The first 24 hours served as a run-in period and the remaining four days (96 hours) served as the actual test weighing period. Infants were weighed (± 1 g accuracy) before and after each feed to determine breast milk intake. A foremilk sample was collected before each feed to determine energy and fat concentration of the milk using the creamatocrit method. Additional mid-feed and hind-milk samples were collected from the first feed each day. Results: Mean breast milk intake was low (369 ± 98 g/day), and infants consumed 52 ± 15 g of milk at each feed. Mean breastfeeding frequency was 7 ± 1 feeds/day. Mean fat and energy concentrations of sampled foremilk were 25.7 ± 7.3 g/L and 2544.5 ± 255.9 KJ/L, respectively. Mean daily fat and energy intake calculated from the measured milk intake was 14 ± 4g and 1096 ± 302 KJ, respectively. Fat concentrations of fore- (26.8 ± 8.2 g/L), mid- (37.6 ± 7.0g/L) and hind-feed- (50.2±10.4 g/L) milk differed significantly (P<0.001). Consequently, energy concentrations of fore- (2522.9 ± 323.2 KJ/L), mid- (2947.1 ± 275.3 KJ/L) and hind-feed (3463.5 ± 409.6 KJ/L) milk differed (P<0.001). Milk fat concentration was significantly lower at night than the evening (P=0.015).Milk energy concentration was significantly lower at night than the morning, day and the evening (P<0.05). There were no differences in breast milk intake (grams) between the four days (P=0.371). However, breast milk fat and energy concentration was significantly lower at day 4 than at days 1 and 3 (P<0.05). Prevalence of stunting, underweight and wasting amongst the infants were 39.1%, 13.6% and 4.8%, respectively. Conclusion Breast milk and consequently energy intakes were low in this small sample of exclusively breastfed South African infants. This may explain the high prevalence of stunting. However, the change of environment and feeding pattern during the study could have affected milk production or intake. Furthermore, test weighing may not be a well-suited method for establishing milk intake in this population. Our results further confirm significant within-feed differences in breast milk fat and energy concentration