Circadian variation in fat concentration of breast-milk in a rural northern Thai population

Abstract

I. Twenty-five northern Thai mothers, breast-feeding their infants on demand, were studied in their homes for 24 h. All breast-feeds were test-weighed and pre-and post-feed expressed breast-milk samples (0.5 ml) taken at each feed.2. The fat concentration of milk taken during a feed showed significant circadian variation, with maximum values between 16.00 and 20.00 hours and minimum values between 04.00 and 08.00 hours. Fat concentration at the start and at the end of a feed also varied significantly over 24 h.3. Multiple regression analysis showed that the most important predictor of fat concentration at a feed was the length of time elapsed since the previous feed -the longer this interval, the lower the subsequent fat concentration. Other significant predictors were the fat concentration at the end of the previous feed, and the milk intake at the previous and at the current feed.4. Fat concentration declined between feeds in proportion to the length of time between feeds, but the decline was less between sleep feeds than between waking feeds. This would appear to be a reflection of the lower postfeed fat concentration and higher pre-feed fat concentration of sleep feeds compared with waking feeds, when other variables relating to feeding pattern are taken into account.5. The larger the milk intake at a feed, the greater was the increase in fat concentration from the start to the end of the feed. The change in fat concentration was less in feeds taking place during the sleep period than in daytime feeds.Fat is the main source of energy of the breast-fed infant. Fat is also the most variable constituent of breast-milk, fluctuating in concentration over the course of a 24 h period (Hytten, 1 9 5 4~; Prentice et al. 1981 a ; Brown et al. 1982) and also rising during individual breast-feeds (Williams et al. 1986). Information on variation in breast-milk fat concentration is useful for planning breast-milk sampling procedures to obtain representative measures of the infant's energy intake. Descriptions of variations in breast-milk composition may also contribute to an understanding of those aspects of the physiology of human lactation which are not amenable to in vivo experimentation.Most of the information on circadian variation in breast-milk fat concentration was obtained from studies carried out in the West when scheduled feeding of the infant was fashionable. Breast-milk was therefore sampled at regular intervals corresponding to feeds (

Estimation of 24 h breast-milk fat concentration and fat intake in rural northern Thailand

“…On average, in this study group, fat concentration is closest to the 24 h mean fat concentration between 08.00 and 12.00 hours and between 12.00 and 16.00 hours (Jackson et al 1988) with less variance in the 12.00-16.00 hours period. The mean fat concentration of the first two feeds after 12.00 hours (' 12.00 hours feeds') was therefore used to estimate 24 h concentration.…”

“…'Daytime' refers to the period when the mother was awake, 'night-time' to the time when mother and baby were asleep together. Further descriptions of the study group and methods are given in Jackson et al (1988).…”

“…In this population mean fat concentration of breast-milk is lowest between 04.00 and 08.00 hours while peak values occur between 16.00 and 20.00 hours (Jackson et al 1988). An early and a late feed might therefore be representative of average milk composition over 24 h. Predictor fat concentration was taken as the mean of the first feed of the study day, which began at 08.00 hours ('08.00 hours feed') and the first feed after 18.00 hours (' 18.00 hours feed').…”

“…Since the fat concentration of breast-milk shows circadian variation (Hytten, 1954;Brown et al 1982;Prentice et al 1981 ;Jackson et al 1988) it is important to obtain milk samples which are representative of the composition of milk consumed over a 24 h period. If repeated measurements are made on the same mother, the samples should be small to avoid interfering with lactation and the infant's feeding pattern (Jackson et a/.…”

Synthesis and secretion of fat in human milk and its role in infant development

“…The major predictors of content of fat in milk over the course of a day have been shown to be the length of the interval between breastfeeds,the fat content at the end of the previous breastfeed,the amount of milk removed at the previous breastfeed and the amount of milk removed at the current feed (Jackson et al,1988).…”