Effects of Different Thawing and Warming Processes on Human Milk Composition.

The composition of human milk is influenced by storage and processing practices. The effects of thawing and warming practices on human milk composition remain poorly studied despite their prevalence in home, research, and donor milk bank settings. This review comprehensively examines the impact of different thawing and warming methods on nutritional and bioactive human milk components. While some components such as carbohydrates and minerals remain stable under most typical thawing and warming conditions, others, such as fat, immune proteins, bacterial and human cells, and peptide amine hormones, are sensitive to warming. This review has identified that the data on the effects of milk thawing and warming is limited and often contradictory. Given that numerous important components of milk are diminished during cold storage, it is important that thawing and warming practices do not lead to further loss of or alterations to beneficial milk components. Further work in this field will facilitate greater standardization of thawing methods among researchers and underpin recommendations for thawing and warming of expressed milk for parents.

Milk microbiome transplantation: recolonizing donor milk with mother's own milk microbiota.

Donor human milk (DHM) provides myriad nutritional and immunological benefits for preterm and low birthweight infants. However, pasteurization leaves DHM devoid of potentially beneficial milk microbiota. In the present study, we performed milk microbiome transplantation from freshly collected mother's own milk (MOM) into pasteurized DHM. Small volumes of MOM (5%, 10%, or 30% v/v) were inoculated into pasteurized DHM and incubated at 37 °C for up to 8 h. Further, we compared microbiome recolonization in UV-C-treated and Holder-pasteurized DHM, as UV-C treatment has been shown to conserve important biochemical components of DHM that are lost during Holder pasteurization. Bacterial culture and viability-coupled metataxonomic sequencing were employed to assess the effectiveness of milk microbiome transplantation. Growth of transplanted MOM bacteria occurred rapidly in recolonized DHM samples; however, a greater level of growth was observed in Holder-pasteurized DHM compared to UV-C-treated DHM, potentially due to the conserved antimicrobial properties in UV-C-treated DHM. Viability-coupled metataxonomic analysis demonstrated similarity between recolonized DHM samples and fresh MOM samples, suggesting that the milk microbiome can be successfully transplanted into pasteurized DHM. These results highlight the potential of MOM microbiota transplantation to restore the microbial composition of UV-C-treated and Holder-pasteurized DHM and enhance the nutritional and immunological benefits of DHM for preterm and vulnerable infants. KEY POINTS: • Mother's own milk microbiome can be successfully transplanted into donor human milk. • Recolonization is equally successful in UV-C-treated and Holder-pasteurized milk. • Recolonization time should be restricted due to rapid bacterial growth.

Associations of Secretory Activation Breast Milk Biomarkers with Breastfeeding Outcome Measures.

OBJECTIVE: The objective of this study was to explore associations between day 10 postpartum (D10) secretory activation biomarkers and the breastfeeding outcome measures. STUDY DESIGN: This prospective longitudinal descriptive study collected antepartum, D10, and day 60 postpartum (D60) questionnaire data and D10 milk samples. Protein, lactose, and citrate were analyzed with enzymatic spectrophotometric assays. Sodium and potassium were analyzed with inductively coupled plasma optical emission spectrophotometry. Group comparison data were analyzed using χ2, Fisher exact, and independent sample t tests, as appropriate, using SPSS for Mac (version 28). RESULTS: Participants (n = 92) provided a D10 breastmilk sample and completed D10 questionnaires, and 83 completed D60 questionnaires. Participants with D10 impaired secretory activation sodium (>23.0 mM) were more likely to report D10 perceived insufficient milk supply, χ2 = 7.002, P < .05; and less D10 feeding/pumping frequency a day, P < .05; and partial breastfeeding at D60, P < .05. Additionally, participants with D10 impaired secretory activation sodium-to-potassium ratio (sodium: potassium) > 0.8 were more likely to partially breastfeed at D60, P < .05. CONCLUSION: Elevated milk sodium and sodium: potassium are biomarkers related to variables indicative of low milk supply. Therefore, immediate milk testing can be useful in identifying lactation compromise and improving breastfeeding duration. Because breastfeeding affords maternal and infant health benefits, clinicians should identify ways to measure lactation compromise in conjunction with an examination and clinical history to provide early interventions to increase breastfeeding duration and exclusivity.

Delayed secretory activation and low milk production in women with gestational diabetes: a case series.

BACKGROUND: Gestational diabetes mellitus (GDM) is major pregnancy complication that is associated with short- and long-term consequences for both mother and infant, including increased risk of diabetes later in life. A longer breastfeeding duration has been associated with a reduced risk of diabetes, however, women with GDM are less likely to exclusively breastfeed and have shorter breastfeeding duration. While the timing of breastfeeding initiation and milk removal frequency affects subsequent breastfeeding outcomes, little is known about early infant feeding practices and milk production in women with GDM. This case series offers detailed prospective breastfeeding initiation data, as well as the first report of objective measures of milk production in women with GDM. CASE PRESENTATION: In this case series, we present the early infant feeding practices of eight women with GDM that gave birth at term gestation. Women recorded the timing of initiation of breastfeeding and secretory activation, as well as their breastfeeding, expression and formula feeding frequencies on postpartum days 1, 7 and 21. Measurement of 24 h milk production volume was performed at 3 weeks postpartum using the test weight method. We observed a delayed first breastfeed (> 1 h) in 6 (75%) cases, formula use in hospital in 5 (63%) cases and delayed secretory activation in 3 (38%) cases. At 3 weeks postpartum, 2 cases had measured milk productions that were insufficient to sustain adequate infant weight gain. CONCLUSIONS: Our data suggest that despite early and frequent milk removal, women with GDM are at greater risk of delayed secretory activation and low milk supply. Cohort studies that consider co-morbidities such as obesity are needed to determine the lactation outcomes of women with GDM.

Exclusively Breastfed Infant Microbiota Develops over Time and Is Associated with Human Milk Oligosaccharide Intakes.

Temporal development of maternal and infant microbiomes during early life impacts short- and long-term infant health. This study aimed to characterize bacterial dynamics within maternal faecal, human milk (HM), infant oral, and infant faecal samples during the exclusive breastfeeding period and to document associations between human milk oligosaccharide (HMO) intakes and infant oral and faecal bacterial profiles. Maternal and infant samples (n = 10) were collected at 2−5, 30, 60, 90 and 120 days postpartum and the full-length 16S ribosomal RNA (rRNA) gene was sequenced. Nineteen HMOs were quantitated using high-performance liquid chromatography. Bacterial profiles were unique to each sample type and changed significantly over time, with a large degree of intra- and inter-individual variation in all sample types. Beta diversity was stable over time within infant faecal, maternal faecal and HM samples, however, the infant oral microbiota at day 2−5 significantly differed from all other time points (all p < 0.02). HMO concentrations and intakes significantly differed over time, and HMO intakes showed differential associations with taxa observed in infant oral and faecal samples. The direct clinical relevance of this, however, is unknown. Regardless, future studies should account for intakes of HMOs when modelling the impact of HM on infant growth, as it may have implications for infant microbiota development.

Nipple shield use does not impact sucking dynamics in breastfeeding infants of mothers with nipple pain.

Nipple shields (shield) may reduce pain during breastfeeding, but the impact on infant sucking dynamics is not known. We examined the effects of shield use on sucking dynamics, milk removal and nipple pain in two groups of breastfeeding dyads: pain group (PG): shield used for nipple pain; comparison group (CG): no breastfeeding difficulties. Twenty PG (6 ± 4 weeks postnatal) and 28 CG dyads (8 ± 6 weeks postnatal) attended 2 monitored breastfeeding sessions with shield use randomised. Within-subject outcomes were compared. PG: shield use did not affect intra-oral vacuum (peak p = 0.17, baseline p = 0.59), sucking frequency (p = 0.20) or milk transfer (40 mL vs 48 mL, p = 0.80; percentage of available milk removed (PAMR) 55% vs 57%, p = 0.88), and reduced McGill pain scores (p = 0.012). CG: shield use increased non-nutritive sucking (10% more, p = 0.049), and reduced nutritive sucking (18% less, p = 0.017) and milk transfer (63 mL vs 31 mL p < 0.001, PAMR 65% vs 36% p < 0.001). For both groups, feeding duration increased by 2 min (p < 0.0001) and non-nutritive portions of the feed increased with shield use.Conclusion: Nipple shield use improved maternal comfort and did not impact milk removal or sucking strength in PG, but significantly reduced milk transfer and nutritive sucking in CG. What is Known: • Mothers report that nipple shields reduce nipple pain and enable continued breastfeeding. • Concerns that nipple shield use may reduce milk transfer and alter infant sucking patterns are based on limited published evidence. What is New: • Nipple shield use is associated with a 25% reduction in pain scores in breastfeeding mothers with chronic nipple pain. • Milk transfer is not reduced in dyads that regularly use a shield for chronic nipple pain. • Intra-oral vacuums are not impacted by nipple shield use in mothers experiencing pain.

Human Milk Metabolic Hormones: Analytical Methods and Current Understanding.

Human milk (HM) contains a wide array of peptide hormones including leptin and adiponectin, which are involved in the regulation of infant growth and development. These essential hormones might play an important role in the regulation of metabolic reprogramming of the new-born infant. However, HM hormone studies are sparse and heterogeneous in regard to the study design, sample collection, preparation and analysis methods. This review discussed the limitations of HM hormone analysis highlighting the gaps in pre-analytical and analytical stages. The methods used to quantify HM metabolic hormones (leptin, adiponectin, ghrelin, insulin, obestatin, resistin and apelin) can be classified as immunoassay, immunosensor and chromatography. Immunoassay methods (ELISA and RIA) have been predominantly used in the measurement of these HM hormones. The relative validity parameters of HM hormones analysis are often overlooked in publications, despite the complexity and differences of HM matrix when compared to that of plasma and urine. Therefore, appropriate reports of validation parameters of methodology and instrumentation are crucial for accurate measurements and therefore better understanding of the HM metabolic hormones and their influences on infant outcomes.

Effect of nipple shield use on milk removal: a mechanistic study.

BACKGROUND: Concerns about reduced milk transfer with nipple shield (NS) use are based on evidence from studies with methodological flaws. Milk removal during breastfeeding can be impacted by infant and maternal factors other than NS use. The aim of this study was to control electric breast pump vacuum strength, pattern and duration across multiple study sessions to determine if NS use reduces milk removal from the breast. METHODS: A within-subject study with two groups of breastfeeding mothers (infants < 6 months) were recruited; Control Group (CG): no breastfeeding difficulties; Pain Group (PG) used NS for persistent nipple pain. Mothers completed three randomised 15 min pumping sessions using the Symphony vacuum curve (Medela AG); no NS, fitted NS, and a small NS. Sessions were considered valid where the applied vacuum was within 20 mmHg of the set vacuum. Milk removal was considered as pumped milk volume, and also percentage of available milk removed (PAMR), which is calculated as the pumped volume divided by the estimated milk volume stored in the breast immediately prior to pumping. RESULTS: Of 62 sessions (all: n = 31 paired sessions) a total of 11 paired sessions from both PG (n = 03) and CG (n = 08) were valid (subset) with and without a fitted NS. Only 2 small shield sessions were valid and so all small shield measurements were excluded. Both pumped volumes and PAMR were significantly lower with NS use for all data but not for subset data. (All: Volume and PAMR median: no NS: 76.5 mL, 69%, Fitted NS: 32.1 mL, 41% respectively (volume p = 0.002, PAMR p = 0.002); Subset: Volume and PAMR median: no NS: 83.8 mL, 72%; Fitted NS: 35.2 mL, 40% (volume p = 0.111 and PAMR p = 0.045). The difference in PAMR, but not volume, was statistically significant when analysed by linear mixed modelling. A decrease of 10 mmHg was associated with a 4.4% increase in PAMR (p = 0.017). CONCLUSIONS: This experimental data suggests that nipple shield use may reduce milk removal. Close clinical monitoring of breastfeeding mothers using nipple shields is warranted.

Detection of Milk Ejection Using Bioimpedance Spectroscopy in Lactating Women during Milk Expression Using an Electric Breast Pump.

Milk ejection is essential for effective milk removal during breastfeeding and pumping, and for continued milk synthesis. Many women are unable to accurately sense milk ejection to determine whether their infant is receiving milk or, when pumping, to switch the pump to a more effective expression pattern. To determine if changes in bioimpedance parameters are associated with milk ejection in the lactating breast during pumping. 30 lactating women participated in 2 pumping sessions within 2 weeks of each other. During pumping the breasts were monitored with bioimpedance spectroscopy (on either the pumped or the non- pumped breast), and milk flow rate and volume were measured simultaneously. All mothers completed 24-h milk productions. Linear mixed effects models were used to determine associations between milk flow rate and bioimpedance changes. Changes in bioimpedance parameters were greater at the first milk ejection when measured on the pumped breast (median (IQR): R zero: -7 (-17, -4,) % (n = 30); R infinity: -8 (-20, -2) % (n = 29); membrane capacitance: -24 (-59, -7) % (n = 27). Changes in bioimpedance detected in the non-pumped breast were lower at the first milk ejection, R zero: -3 (-8, -2) % (n = 25); R infinity: -5 (-8, -2) % (n = 23); membrane capacitance: -9 (-17, 15) % (n = 24). Smaller less consistent decreases in the bioimpedance characteristics were detected at the second milk ejection in both breasts. Bioimpedance parameters showed a consistent decrease associated with the first milk ejection when electrodes were placed on the pumped breast. Smaller decreases were observed when the non-pumped breast was monitored for the first and second milk ejection. There was wide variation in the magnitude of changes observed, and hence further development of the methodology is needed to ensure reliability.

Milk ejection patterns remain consistent during the first and second lactations.

OBJECTIVE: Milk ejection is a critical physiological process for successful lactation in humans and without it little milk can be removed. Individual milk ejection patterns have been shown to remain consistent between breasts at different lactation stages and using different vacuum patterns with an electric breast pump. Little is known about the milk ejection characteristics during the second lactation period in the same mother. The objective of this study was to examine milk ejection characteristics in the same woman over two lactations. METHODS: One mother took part in two pumping studies during consecutive lactations. One pumping study examined milk ejection characteristics during simultaneous breast expression during the first lactation. The second pumping study (second lactation) used two different pumping patterns. Three distinct milk ejections were measured during each pumping session. RESULTS: Measurements of milk flow were used to compare the duration and time taken to reach the peak of each milk ejection for two pumping sessions from each of the lactations. There were no significant differences in milk ejection characteristics between breasts, using different pumping patterns, or between lactations in this mother (P > .05). CONCLUSION: Milk ejection appears to be a physiological response that is consistent across consecutive lactations within the same mother. This suggests that milk ejection characteristics are established during or prior to the first lactation. The infant appears to have little influence on the milk ejection characteristics of the mother.

Changes in milk composition associated with pethidine-PCEA usage after Caesarean section.

The effect of pethidine as patient-controlled epidural analgesia (PCEA) on specific biochemical components in breast milk in relation to the timing of secretory activation is not well investigated. The aim of this study was to compare biochemical timing of secretory activation between women who had a vaginal (V) or Caesarean birth with pethidine-PCEA (CBP). Several milk samples were collected daily from 36 mothers (17 V, 19 CBP) for the first 265 h post-partum. Protein and lactose concentrations and Na+ and K+ ion levels were measured. Samples were assigned to three time periods: 0-72, >72-165 and >165-265 h post-partum for statistical analyses. Data were analyzed using linear mixed effect models. In the first 72 h post-partum, the mean difference in lactose concentration was 5 gL-1 higher in group V (P < 0.05). From >72-165 h post-partum, protein and Na+ concentrations were lower in group V (P = 0.05, P = 0.02), and K+ levels were higher in group V (P < 0.001). From >165-265 h post-partum, there were no significant differences between the groups. Biochemically, secretory activation had occurred by 72 h post-partum in both groups. There were greater variations in measured biochemical components observed within group CBP initially. However, by 165 h post-partum, there were no differences in the biochemical components between the groups. This suggests that effects of pethidine-PCEA are diminished by 72 h post-partum and undetected by 165 h.

Levels of innate immune factors in preterm and term mothers' breast milk during the 1st month postpartum.

There is a paucity of data on the effect of preterm birth on the immunological composition of breast milk throughout the different stages of lactation. We aimed to characterise the effects of preterm birth on the levels of immune factors in milk during the 1st month postpartum, to determine whether preterm milk is deficient in antimicrobial factors. Colostrum (days 2-5 postpartum), transitional milk (days 8-12) and mature milk (days 26-30) were collected from mothers of extremely preterm (<28 weeks of gestation, n 15), very preterm (28-<32 weeks of gestation, n 15), moderately preterm (32-<37 weeks of gestation, n 15) and term infants (37-41 weeks of gestation, n 15). Total protein, lactoferrin, secretory IgA, soluble CD14 receptor (sCD14), transforming growth factor-ß2 (TGF-ß2), α defensin 5 (HD5), ß defensins 1 (HBD1) and 2, IL-6, IL-10, IL-13, interferon-γ, TNF-α and lysozyme (LZ) were quantified in milk. We examined the effects of lactation stage, gestational age, volume of milk expressed, mode of delivery, parity and maternal infection on milk immune factor concentrations using repeated-measures regression analysis. The concentrations of all factors except LZ and HD5 decreased over the 1st month postpartum. Extremely preterm mothers had significantly higher concentrations of HBD1 and TGF-ß2 in colostrum than term mothers did. After controlling for other variables in regression analyses, preterm birth was associated with higher concentrations of HBD1, LZ and sCD14 in milk samples. In conclusion, preterm breast milk contains significantly higher concentrations of some immune proteins than term breast milk.

Human Milk Cells Contain Numerous miRNAs that May Change with Milk Removal and Regulate Multiple Physiological Processes.

Human milk (HM) is a complex biofluid conferring nutritional, protective and developmental components for optimal infant growth. Amongst these are maternal cells, which change in response to feeding and were recently shown to be a rich source of miRNAs. We used next generation sequencing to characterize the cellular miRNA profile of HM collected before and after feeding. HM cells conserved higher miRNA content than the lipid and skim HM fractions or other body fluids, in accordance with previous studies. In total, 1467 known mature and 1996 novel miRNAs were identified, with 89 high-confidence novel miRNAs. HM cell content was higher post-feeding (p < 0.05), and was positively associated with total miRNA content (p = 0.014) and species number (p < 0.001). This coincided with upregulation of 29 known and 2 novel miRNAs, and downregulation of 4 known and 1 novel miRNAs post-feeding, but no statistically significant change in expression was found for the remaining miRNAs. These findings suggest that feeding may influence the miRNA content of HM cells. The most highly and differentially expressed miRNAs were key regulators of milk components, with potential diagnostic value in lactation performance. They are also involved in the control of body fluid balance, thirst, appetite, immune response, and development, implicating their functional significance for the infant.

Milk ejection patterns: an intra- individual comparison of breastfeeding and pumping.

BACKGROUND: Milk ejection is a transient episode critical to milk removal and women typically have multiple milk ejections during breastfeeding and pumping. Recently it was found that milk ejection characteristics such as number of milk ejections and periodicity were consistent throughout 12 months of lactation in women who expressed their milk with an electric breast pump. It is not known whether the stimulation of an infant at the breast influences milk ejection patterns or whether this is a programmed event. The aim of this study was to compare milk ejection patterns during breastfeeding and expressing milk with an electric pump within mothers. METHODS: Twelve lactating mothers with normal milk production (502-1356 mL) had milk ejection recorded by measuring the diameter of a major milk duct with ultrasound imaging throughout an entire breastfeed and a 15-min pumping session. Scans were analysed for timing, duration of duct dilation and maximum duct diameter. RESULTS: The initial milk ejection defined as the first increase in duct diameter was observed earlier during breastfeeding than during two phase pumping sessions but was not statistically significant (p = .057). There were no significant differences between the duration of the first or second milk ejection for mothers when breastfeeding or pumping at their maximum comfortable vacuum (p = .18; p = .99). The times taken to reach the peak duct diameter, or the first half of the milk ejection were also not found to be significantly different between breastfeeding and pumping. CONCLUSION: This study suggests that milk ejection patterns remain consistent within individual mothers regardless of whether the mother is breastfeeding or expressing milk indicating a likelihood of the process either being programmed or innate to the individual.

Anti-infective proteins in breast milk and asthma-associated phenotypes during early childhood.

BACKGROUND: The impact of breast milk feeding on susceptibility to asthma in childhood is highly controversial, due in part to failure of the majority of studies in the area to adequately account for key confounders exemplified by respiratory infection history, plus the effects of recall bias. METHODS: As part of a prospective cohort study on the role of respiratory infections in asthma development in high-risk children, we measured the concentration of a panel of anti-infective proteins in maternal milk samples and analyzed associations between these and subsequent atopy-, infection-, and asthma-related outcomes prospectively to age 10 years. RESULTS: We observed significant but transient inverse associations between the concentration of milk proteins and susceptibility to upper respiratory infections in year 1 only, and parallel but positive transient associations with early lower respiratory infections and atopy. No associations were seen with asthma-related outcomes. CONCLUSIONS: Breast milk feeding may influence the expression of inflammatory symptoms associated with respiratory infections and atopy in early life, but these effects appear to be inconsistent and transient. The heterogeneous nature of breast-feeding effects suggests it may influence systemic immunoinflammatory function at several different levels.

Causes of Low Milk Supply: The Roles of Estrogens, Progesterone, and Related External Factors.

Low milk supply (LMS) poses a significant challenge to exclusive and continued breastfeeding, affecting ∼10% to 15% of mothers. Milk production is intricately regulated by both endocrine and autocrine control mechanisms, with estrogens and progesterone playing pivotal roles in this process. In addition to endogenously produced hormones, external substances capable of interfering with normal hormonal actions, including phytoestrogens, mycoestrogens, synthetic estrogens, and hormonal contraceptives, can influence milk production. The effects of these extrinsic hormones on milk production may vary based on maternal body mass index. This comprehensive review examines the multifaceted causes of LMS, focusing on the involvement of estrogens, progesterone, and related external factors in milk production. Furthermore, it investigates the interplay between hormonal factors and obesity, aiming to elucidate the endocrine mechanisms underlying obesity-associated LMS. Insights from this review provide valuable perspectives for developing interventions to improve milk production and address the challenges associated with LMS.

Maternal Breast Growth and Body Mass Index Are Associated with Low Milk Production in Women.

BACKGROUND: Maternal breast volume is determined by the quantity of glandular and adipose tissue, and it undergoes significant changes during pregnancy. These changes are intricately linked to the development of glandular tissue, which most likely reflects lactation capacity. Evidence indicates that women with overweight or obesity exhibit larger breast volume compared to those with a normal body mass index (BMI), emphasizing the close relationship between breast volume and maternal adiposity. Hence, we aim to investigate breast volume growth and maternal BMI as potential risk factors for low milk production. METHODS: Lactating women (n = 609) from the Perth metropolitan area in Western Australia between 2011 and 2023 were included in the analysis. Twenty-four-hour milk production measurements were conducted using the test weighing method, and milk removal frequencies were recorded. Mothers completed questionnaires regarding demographic, obstetric and infant details. Linear and logistic regression models were used to determine maternal and infant factors associated with milk production. RESULTS: Here we show that increasing maternal age and BMI are associated with low milk production. Moreover, larger pre-pregnancy breast volume and breast growth are associated with both higher BMI and milk production. CONCLUSIONS: Women who are older, have an obese BMI and who have minimal pre-pregnancy breast volume and breast growth should be provided with antenatal screening and breastfeeding support as they are more likely to experience low milk production.

Sampling Procedures for Estimating the Infant Intake of Human Milk Leptin, Adiponectin, Insulin, Glucose, and Total Lipid.

Limited attention is given to the efficacy of protocols for the estimation of infant intake of milk components when investigating their impact on infant outcomes. We compared the actual measured intake of human milk components with estimations derived from 15 protocols to determine the most reliable approach for estimating intake of HM leptin, adiponectin, insulin, glucose, and total lipid. Twenty mothers who were 3-5 months postpartum completed a 24 h milk profile study with pre-/post-feed milk samples collection. The true infant intake (control group) based on 24 h milk intake (MI) was compared to estimated infant intakes using concentrations from five sampling protocols that were multiplied by one of true infant MI, considered mean MI (800 mL), or global mean MI (766 mL). The mean measured concentrations of six samples (three sets of pre- and post-feed samples, from morning (06:00-09:00), afternoon (13:00-16:00), and evening (19:00-22:00)) multiplied by the true infant MI, mean considered MI, and global mean MI produced the most accurate estimates of infant intake of these components. Therefore, in the absence of 24 h measurements and sampling, a sampling protocol comprising three sets of pre-/post-feed samples provides the most reliable infant intake estimates of HM leptin, adiponectin, insulin, glucose, and total lipid.

Macronutrients in Human Milk and Early Childhood Growth-Is Protein the Main Driver?

BACKGROUND: Infant growth trajectories reflect current health status and may predict future obesity and metabolic diseases. Human milk is tailored to support optimal infant growth. However, nutrient intake rather than milk composition more accurately predicts growth outcomes. Although the role of protein leverage in infant growth is unclear, protein intake is important for early infancy growth. MATERIALS AND METHODS: This study of exclusively breastfeeding mothers with allergies (n = 161) from the Infant Fish Oil Supplementation Study assessed relationships between intake of human milk macronutrients and infant growth. Human milk fat, protein and lactose concentrations were measured at 3 months postpartum, and infant daily intakes were estimated using an average milk intake of 800 mL/day. RESULTS: Higher human milk protein:energy ratio was associated with higher weight-for-age z-score at 2.5 years compared to 3 months and higher body mass index-for-age z-score change (6 months to 1 year compared to 3-6 months). Maternal atopy and birth season (summer) were negatively associated with human milk lactose concentration. Passive smoke exposure was associated with reduced energy and fat concentrations and increased lactose:energy ratio. CONCLUSIONS: Our results indicate that intake of human milk macronutrients may impact early childhood growth.

Investigation of Relationships between Intakes of Human Milk Total Lipids and Metabolic Hormones and Infant Sex and Body Composition.

Human milk (HM) composition, including metabolic hormones and lipids, is influenced by various factors, including lactation stage and, potentially, infant sex, which may affect infant body composition (BC) development. We aimed to: (a) characterize the longitudinal concentration and intake profiles of HM leptin, adiponectin, insulin, and total lipids; (b) determine if their concentrations and intakes differ by infant sex; and (c) explore the intakes relationships with the development of infant BC. Milk samples (n = 501) were collected from 82 mother-infant dyads during the first 6 months postpartum. Infant 24 h HM intake was measured, and the average cumulative HM component intakes were calculated. The statistical analysis used linear mixed modeling. Intakes of HM leptin, adiponectin, insulin, and total lipids increased to 1 month postpartum and then remained stable. HM intake and total lipids intake but not hormone intakes were positively associated with infant BC (fat-free mass, fat-free mass index, fat mass, fat mass index, percentage fat mass, and fat mass to fat-free mass ratio). HM component concentrations and intakes did not differ by sex. These findings advance our understanding of the temporal nature of HM components, emphasizing the role of infant 24 h HM and total lipids intake in development of infant lean and adipose tissue.