Human Milk Sampling Protocols Affect Estimation of Infant Lipid Intake

BACKGROUND: Human milk (HM) lipid content is highly variable, and infants consume different volumes of milk. This makes precise sampling and calculation of the infant lipid intake problematic. OBJECTIVES: In order to describe inaccuracies of estimates of lipid content introduced by various sampling protocols, we compared the true infant lipid intake with estimated intakes using different milk sampling protocols. METHODS: Monthly milk samples (n = 1026) from months 1 to 6 of lactation were collected from 20 healthy, exclusively breastfeeding women. Infant lipid intake was measured by 24-hour test-weighing at month 3. Total lipid content was measured by creamatocrit. Concentrations and infant lipid intakes were calculated using 11 sampling protocols, using either the true milk intake or an average of 800 mL/d. These estimates were compared with the true infant lipid intake using repeated-measures ANOVA and linear mixed modeling with multiple comparisons. RESULTS: The mean maternal age was 32.0 years (SD ± 3.10), and infants were born term (40.1 ± 1.1 weeks) with a mean birth weight of 3.87 kg (SD ± 0.39). The mean true infant lipid intake was 28.6 g/d (SD ± 9.8). The mean estimated lipid intake using 1 morning pre-feed sample underestimated intake by >8.0 g/d. Estimates of infant lipid intake using other sampling protocols and an assumed intake volume of 800 mL/d also resulted in a wide range of differences (0.8–18.1 g/d) from the true intake. Use of 6 daily pre- and post-feed milk samples had a mean difference of only 0.1 g/d (95% CI, −2.9 to 2.7) from the true intake. CONCLUSIONS: A sampling protocol with 6 pre- and post-feed samples provides the most accurate estimate of lipid intake if it is not possible to perform 24-hour test weights. The potential inaccuracies of sampling protocols should be taken into consideration in the interpretation and translation of infant lipid intake results.