Maternal perceptions of human milk expression output: An experimental design using photographs of milk.

BACKGROUND: The widespread use of breast pumps in the United States is a recent phenomenon that is reshaping how individuals understand and perceive lactation. In the 1990s, adequacy of milk supply was primarily measured indirectly by infant weight gain and/or diapers; now >95% of all lactating persons in the United States use breast pumps and are seeing their milk regularly. How seeing milk impacts the perception of lactation sufficiency is an important area of research. Research aim/question: To understand personal and intersubjective influences of seeing expressed human milk on perceptions of milk supply among participants who express milk for their infants. METHODS: We surveyed 805 lactating participants from the United States about their pumping practices using an online survey. Participants described pumping practices, milk output, and beliefs. They were then randomized to view one of three photographs of expressed milk (<2 oz, 4 oz, >6oz) and asked to imagine they had just pumped that amount and provide a written response; this created 4 exposure groups (2 increase and 2 decrease) and a control group (no difference). RESULTS: Participants randomized to a higher volume reported more positive feelings and used the terms "good", "great", and "accomplished" to describe emotional responses to output. Participants randomized to lower milk volumes reported more feelings of "bad" or "depressed." A subset of participants reported feeling "annoyed" about small volumes of milk. CONCLUSIONS: Participants in this study were very conscious of the volume of milk pumped each session; both increases and decreases were associated with emotional responses that could contribute to decisions about pumping practices, perceived milk supply, and lactation duration.

Childhood growth and education migration among ethnic Tibetan children from Nepal.

BACKGROUND: Ethnographic work among high altitude populations has shown that children are highly mobile-the most recent expression of this is the educational migration of children born at high altitude to boarding schools at lower altitudes. The impact of these patterns of migration on size for age are unknown. AIM: We investigated the association between growth in weight and height and educational migration in ethnic Tibetan children living in and out of their natal communities. SUBJECTS AND METHODS: Five hundred and fifty eight children ages three to sixteen from the Nubri Valley, Nepal participated in this study. Three hundred children were living in natal villages and 258 were attending boarding schools in Kathmandu. Height, weight, and skinfold thicknesses were collected and matched to demographic data from the community. RESULTS: There was no association between altitude of family residence and size for age z-scores. Males had lower z-scores than females; z-scores for both groups declined with age. Differences in size for age among children in boarding schools were associated with two factors: sex and type of boarding school (individual sponsor or group funded). Individuals attending individually sponsored schools had greater size for age compared to children in group funded schools or in their natal villages; younger children in collectively funded schools were smaller than village peers. CONCLUSIONS: Despite popular perceptions, educational outmigration in Himalayan communities may not be associated with improved child growth outcomes and investment in community level schools may be a practical solution for improving child growth and physical and mental health.

Child dietary patterns in Homo sapiens evolution: A systematic review.

Dietary patterns spanning millennia could inform contemporary public health nutrition. Children are largely absent from evidence describing diets throughout human evolution, despite prevalent malnutrition today signaling a potential genome-environment divergence. This systematic review aimed to identify dietary patterns of children ages 6 months to 10 years consumed before the widespread adoption of agriculture. Metrics of mention frequency (counts of food types reported) and food groups (globally standardized categories) were applied to: compare diets across subsistence modes [gatherer-hunter-fisher (GHF), early agriculture (EA) groups]; examine diet quality and diversity; and characterize differences by life course phase and environmental context defined using Köppen-Geiger climate zones. The review yielded child diet information from 95 cultural groups (52 from GHF; 43 from EA/mixed subsistence groups). Animal foods (terrestrial and aquatic) were the most frequently mentioned food groups in dietary patterns across subsistence modes, though at higher frequencies in GHF than in EA. A broad range of fruits, vegetables, roots and tubers were more common in GHF, while children from EA groups consumed more cereals than GHF, associated with poor health consequences as reported in some studies. Forty-eight studies compared diets across life course phases: 28 showed differences and 20 demonstrated similarities in child versus adult diets. Climate zone was a driver of food patterns provisioned from local ecosystems. Evidence from Homo sapiens evolution points to the need for nutrient-dense foods with high quality proteins and greater variety within and across food groups. Public health solutions could integrate these findings into food-based dietary guidelines for children.

Centering human milk composition as normal human biological variation.

OBJECTIVES: Human biological variation in the phenotype is the cornerstone of modern human biology, evolutionary anthropology, and related studies of human evolution. Minimal dialogue, however, has considered human milk to be part of this phenotypic variation. This may reflect researcher bias-mental models oriented around commercial infant formula and homogenized cow's milk, both of which present milk composition as static. A general lack of research outside primarily Western, well-nourished populations has also contributed to this underestimation of biological variation. METHODS: This review analyzes published research on breast milk composition, developmental metabolic programming, and maternal body composition to articulate the ways in which population-based studies of human milk outside the United Sates are necessary to better understanding biological variation in human milk phenotypes. RESULTS: This review discusses some of the common issues in current research on the biological variation in human milk composition and argues that anthropological inquiries that frame milk as part of an adaptive phenotype are necessary to better understand the biological significance of human milk composition in the production of human biological variation. CONCLUSIONS: Biological anthropology is uniquely positioned to investigate biological variation in human milk, using evolutionary theory, cutting edge biology, and anthropologically informed perspectives that challenge the biomedical framing of lactation and often act to privilege well nourished, primarily western populations and formula feeding as normatives for infant feeding research.

Navigating cross-cultural research: methodological and ethical considerations.

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour.

Trekking and toddlers: Towards a biocultural analysis of growth among infants and young children in a rural region of the Himalayas.

OBJECTIVES: Rapid socioeconomic change, associated with development and a growing tourism industry is occurring across the Himalayas. The health impact of this rapid economic development is poorly understood, especially for infants and young children. This study investigated the associations between village level economic differences as indexed by economic development and tourism engagement on infant and young child growth and health in a population of ethnic Tibetans living in the western Himalayas of Nepal. METHODS: One hundred and fifty nine infants and young children (ages 1-24 months) were enrolled. Anthropometric data (height, weight, triceps skinfold thickness) were collected at a single time point. Village level measurements of tourism and market engagement were incorporated into a scale measuring tourism, healthcare, trail access, agriculture, and involvement in medicinal trade. Village level disease patterns were calculated from morbidity and mortality recalls collected since 2003. RESULTS: There were no significant associations between infant weight for age z-score (WAZ), length for age z-score (LAZ), or weight-for-length for age z-score (WLZ) and village altitude, village economic development score, or engagement in tourism. Males had significantly higher LAZ, WAZ, and WLZ compared to females; only females showed a decline in LAZ with age. Triceps skinfold thickness z-score (ZTSF) was inversely associated with village level economic development score in male but not female infants; females ZTSF was positively associated with IYC age. CONCLUSIONS: While overall size for age indices (WAZ, LAZ, WLZ) were not associated with altitude or village economic development in this population, ZTSF was inversely associated with village economic development in males but not females.

Evolutionary life history theory as an organising framework for cohort studies: insights from the Cebu Longitudinal Health and Nutrition Survey.

By tracking a group of individuals through time, cohort studies provide fundamental insights into the developmental time course and causes of health and disease. Evolutionary life history theory seeks to explain patterns of growth, development, reproduction and senescence, and inspires a range of hypotheses that are testable using the longitudinal data from cohort studies. Here we review two decades of life history theory-motivated work conducted in collaboration with the Cebu Longitudinal Health and Nutrition Survey (CLHNS), a birth cohort study that enrolled more than 3000 pregnant women in the Philippines in 1983 and has since followed these women, their offspring and grandoffspring. This work has provided evidence that reproduction carries "costs" to cellular maintenance functions, potentially speeding senescence, and revealed an unusual form of genetic plasticity in which the length of telomeres inherited across generations is influenced by reproductive timing in paternal ancestors. Men in Cebu experience hormonal and behavioural changes in conjunction with changes in relationship and fatherhood status that are consistent with predictions based upon other species that practice bi-parental care. The theoretical expectation that early life cues of mortality or environmental unpredictability will motivate a "fast" life history strategy are confirmed for behavioural components of reproductive decision making, but not for maturational tempo, while our work points to a broader capacity for early life developmental calibration of systems like immunity, reproductive biology and metabolism. Our CLHNS findings illustrate the power of life history theory as an integrative, lifecourse framework to guide longitudinal studies of human populations.

Maternal birth weight is associated with milk epidermal growth factor in Filipino women.

OBJECTIVES: Lactational programming, through which milk-borne bioactives influence both neonatal and long-term biological development, is well established. However, almost no research has investigated how developmental stimuli during a mother's early life may influence her milk bioactives in adulthood. Here, we investigated the association between maternal birth weight and milk epidermal growth factor (EGF) and epidermal growth factor receptor (EGF-R) in later life. We predicted there would be a decrease in both milk EGF and EGF-R in the milk produced by mothers who were themselves born low birth weight. METHODS: Study participants are from the Cebu Longitudinal Health and Nutrition Survey. Mothers (n = 69) were followed longitudinally since birth with prospective data collection. Anthropometrics, health, and dietary recalls were collected with early morning milk samples when mothers were 24 to 25 years of age. Milk samples were analyzed for EGF and its receptor (EGF-R). Analysis of variance was used to test for differences in milk EGF and EGF-R between low and average birthweight mothers after adjustment for parity, age, and maternal dietary energy intake. RESULTS: Mothers who were low birth weight produced milk with significantly less EGF and more EGF-R which resulted in a lower ratio of EGF to EGF-R. These associations persisted after adjustment for infant age, maternal adiposity, and dietary energy. CONCLUSIONS: While this is a small sample size, these preliminary findings suggest that maternal early life characteristics, such as birth weight, may be important contributors to variation in milk bioactives. Future work is necessary to understand how variation in maternal early life may influence milk composition in adulthood.

Salivary secretory immunoglobulin A variation between female varsity athletes and nonathletes.

OBJECTIVES: Exercise can lead to changes in immune function. To further investigate this relationship, we examined possible differences in salivary secretory immunoglobulin A (sIgA) secretion rates among female college athletes and nonathlete students. We predicted that athletes would have higher sIgA secretion rates than nonathletes and show greater declines in sIgA during the study period as intensive exercise training continued. METHODS: We recruited 52 female participants aged 18-22 years (13 swimmers, 20 runners, and 19 nonathletes). We collected two saliva samples from each participant: baseline and a second sample 2 weeks later. Additionally, participants reported minutes of cardiovascular activity performed per week and completed a survey that included a modified Profile of Mood States and the Undergraduate Stress Questionnaire. RESULTS: We found no significant differences in mean salivary sIgA secretion rates between athletes and nonathletes. Salivary sIgA significantly increased between sample collections for both groups, with nonathletes exhibiting a greater increase in sIgA than athletes. Cardiovascular activity was not associated with sIgA secretion rates. Illness status was a significant positive predictor of sIgA secretion rates. CONCLUSIONS: Cardiovascular activity did not predict salivary sIgA secretion rates in this sample of female college students, and athletes did not show significantly different sIgA secretion rates than nonathletes. Together, these findings suggest that exercise may not be associated with altered immune function in well-nourished college-aged women. The increase in secretion rates among both athletes and nonathletes suggests that additional factors shared by both groups may have led to increases.

Diversity and temporal dynamics of primate milk microbiomes.

Milk is inhabited by a community of bacteria and is one of the first postnatal sources of microbial exposure for mammalian young. Bacteria in breast milk may enhance immune development, improve intestinal health, and stimulate the gut-brain axis for infants. Variation in milk microbiome structure (e.g., operational taxonomic unit [OTU] diversity, community composition) may lead to different infant developmental outcomes. Milk microbiome structure may depend on evolutionary processes acting at the host species level and ecological processes occurring over lactation time, among others. We quantified milk microbiomes using 16S rRNA high-throughput sequencing for nine primate species and for six primate mothers sampled over lactation. Our data set included humans (Homo sapiens, Philippines and USA) and eight nonhuman primate species living in captivity (bonobo [Pan paniscus], chimpanzee [Pan troglodytes], western lowland gorilla [Gorilla gorilla gorilla], Bornean orangutan [Pongo pygmaeus], Sumatran orangutan [Pongo abelii], rhesus macaque [Macaca mulatta], owl monkey [Aotus nancymaae]) and in the wild (mantled howler monkey [Alouatta palliata]). For a subset of the data, we paired microbiome data with nutrient and hormone assay results to quantify the effect of milk chemistry on milk microbiomes. We detected a core primate milk microbiome of seven bacterial OTUs indicating a robust relationship between these bacteria and primate species. Milk microbiomes differed among primate species with rhesus macaques, humans and mantled howler monkeys having notably distinct milk microbiomes. Gross energy in milk from protein and fat explained some of the variations in microbiome composition among species. Microbiome composition changed in a predictable manner for three primate mothers over lactation time, suggesting that different bacterial communities may be selected for as the infant ages. Our results contribute to understanding ecological and evolutionary relationships between bacteria and primate hosts, which can have applied benefits for humans and endangered primates in our care.

Variation among populations in the immune protein composition of mother's milk reflects subsistence pattern.

LAY SUMMARY: Adaptive immune proteins in mothers' milk are more variable than innate immune proteins across populations and subsistence strategies. These results suggest that the immune defenses in milk are shaped by a mother's environment throughout her life. BACKGROUND AND OBJECTIVES: Mother's milk contains immune proteins that play critical roles in protecting the infant from infection and priming the infant's developing immune system during early life. The composition of these molecules in milk, particularly the acquired immune proteins, is thought to reflect a mother's immunological exposures throughout her life. In this study, we examine the composition of innate and acquired immune proteins in milk across seven populations with diverse disease and cultural ecologies. METHODOLOGY: Milk samples (n = 164) were collected in Argentina, Bolivia, Nepal, Namibia, Philippines, Poland and the USA. Populations were classified as having one of four subsistence patterns: urban-industrialism, rural-shop, horticulturalist-forager or agro-pastoralism. Milk innate (lactalbumin, lactoferrin and lysozyme) and acquired (Secretory IgA, IgG and IgM) protein concentrations were determined using triple-quadrupole mass spectrometry. RESULTS: Both innate and acquired immune protein composition in milk varied among populations, though the acquired immune protein composition of milk differed more among populations. Populations living in closer geographic proximity or having similar subsistence strategies (e.g. agro-pastoralists from Nepal and Namibia) had more similar milk immune protein compositions. Agro-pastoralists had different milk innate immune protein composition from horticulturalist-foragers and urban-industrialists. Acquired immune protein composition differed among all subsistence strategies except horticulturist-foragers and rural-shop. CONCLUSIONS AND IMPLICATIONS: Our results reveal fundamental variation in milk composition that has not been previously explored in human milk research. Further study is needed to understand what specific aspects of the local environment influence milk composition and the effects this variation may have on infant health outcomes.

When women work: Endocrine reactivity in women during everyday physical activity at high altitude.

OBJECTIVES: This study explores the acute endocrine reactivity of testosterone and cortisol in women engaging in everyday physical activity in a high altitude environment. METHODS: Data were collected from 35 women living in the Himalayas, with women recruited from both high (>10 000 ft.) and low altitude villages (<10 000 ft.). Saliva samples were collected at 3 time points (pre-activity, 30 and 60 minutes) and women wore the wGT3X-BT Actigraph during an hour of everyday work to assess the relationship between high altitude, endocrine reactivity, and physical activity. Saliva samples were then analyzed for testosterone and cortisol. RESULTS: Women living at high altitude had lower cortisol and testosterone levels, after controlling for moderate-to-vigorous physical activity, age, and sum of skinfolds. CONCLUSIONS: Testosterone and cortisol increase allocation of energy to costly somatic tissues and the utilization of stored energy. Lower production of these hormones may be beneficial for heightened energetic demands at high altitude.

Ecological pressures and milk metabolic hormones of ethnic Tibetans living at different altitudes.

BACKGROUND: Very little is known about how milk hormones, shown to influence growth during infancy, may contribute to patterns of altered growth in high altitude living infants. AIM: This study investigated the association between maternal BMI, the metabolic hormones adiponectin and leptin in human milk and infant weight for age z-scores (WAZ) in Tibetans. SUBJECTS AND METHODS: A sample of 116 mothers and infants (aged 0-36 months) were recruited from two locations: the Nubri Valley, Nepal (rural; altitude = 2400-3900 m) and Kathmandu, Nepal (urban, 1400 m). Milk samples, anthropometrics, biological data and environmental information were collected on mothers and infants. Milk was analysed for leptin and adiponectin. RESULTS: Maternal BMI was significantly associated with milk leptin content, but not adiponectin in either group. In the rural high altitude sample, child WAZ declined with age, but no such decline was seen in the urban sample. CONCLUSIONS: Milk leptin and adiponectin were not associated with infant growth in the rural Nubri sample, but were both inversely associated with infant WAZ in the Kathmandu sample. It appears that, in ecologically stressful environments, associations between milk hormones and growth during infancy may not be detectable in cross-sectional studies.

Milk at altitude: Human milk macronutrient composition in a high-altitude adapted population of Tibetans.

OBJECTIVE: The physiological challenges of high altitude have led to population-specific patterns of adaptation. These include alterations to child growth and reproduction, including lactation. However, while breastfeeding has been investigated, nothing is known about milk composition in high altitude adapted populations. MATERIALS AND METHODS: Here, we investigate milk macronutrient composition, volume, and energy in a sample of 82 Tibetans living at high and low altitude in rural villages (Nubri Valley, Nepal) and at low altitude in Kathmandu, Nepal. Milk samples were collected in the morning using hand expression, frozen, and assayed for fat, protein, and total sugars. Reproductive histories and health recalls were also collected. RESULTS: Milk fat averaged 5.2 ±2.0 g/100 mL, milk sugar 7.37 ± 0.49 g/100 mL, and milk protein 1.26 ± 0.35 g/100 mL for a mean energy density of 81.4 ± 17.4 kcal/100 mL. There were no associations between altitude of residence and milk composition; however, overall milk fat was high compared to reference populations. Within the three groups, milk fat was positively associated with infant age (B = 0.103; p < 0.001) and maternal triceps skinfold thickness (B = 0.095; p < 0.01) while milk sugar was significantly and inversely associated with maternal parity and triceps skinfold thickness. DISCUSSION: Milk fat, and consequently milk energy, may be increased in high-altitude adapted Tibetans when compared to populations living at low altitude. The association between milk fat and maternal adiposity suggests that milk composition may be sensitive to maternal adiposity in this sample, likely reflecting increased metabolic costs of producing a high-fat milk.

Lower levels of human milk adiponectin predict offspring weight for age: a study in a lean population of Filipinos.

Prior studies have reported a significant, inverse association between adiponectin in human milk and offspring growth velocity. Less is known about this association in populations characterised by a loss of weight for age z-scores (WAZs) in early life. We investigated the association between maternal body composition and milk adiponectin in a sample of Filipino mothers. We then tested for an association between milk adiponectin and size for age in their infants. A total of 117 Filipino mothers nursing infants from 0 to 24 months were recruited from Cebu, Philippines. Anthropometrics, interviews and milk samples were collected and analysed using standard protocols. Mean milk adiponectin in this sample was 7.47 ± 5.75 ng mL(-1) . Mean infant WAZ and weight for length (WLZ) decreased with age. Maternal body composition was not associated with milk adiponectin content. Milk adiponectin had a significant, positive association with infant WAZ and WLZ. Prior reports have found an inverse association between milk adiponectin and infant WAZ. Here, we report that in lean populations with lower milk adiponectin, there is a positive association with infant WAZ, possibly reflecting pleiotropic biological functions of adiponectin for post-natal growth. This study increases the understanding of normal biological variation in milk adiponectin and the consequences of low levels of milk adiponectin for offspring growth.

Maternal characteristics associated with milk leptin content in a sample of Filipino women and associations with infant weight for age.

BACKGROUND: Human milk contains many metabolic hormones that may influence infant growth. Milk leptin is positively associated with maternal adiposity and inversely associated with infant growth. Most research has been conducted in populations with higher leptin levels; it is not well understood how milk leptin may vary in lean populations or the associations that reduced leptin may have with infant size for age. It is also largely unknown if associations between maternal body composition and milk leptin persist past 1 year of age. OBJECTIVES: We investigated the association between maternal body composition and milk leptin content in a sample of lean Filipino women and the association between milk leptin content and infant size for age. METHODS: Milk samples were collected at in-home visits from 113 mothers from Cebu, Philippines. Milk leptin content was measured using EIA techniques; anthropometric data, dietary recalls, and household information were also collected. RESULTS: Mean ± standard deviation (SD) milk leptin in this sample was 300.7 ± 293.6 pg/mL, among the lowest previously reported. Mean ± SD maternal percentage body fat was 24.8% ± 3.5%. Mean ± SD infant age was 9.9 ± 7.0 months, and mean ± SD weight for age z-score was -0.98 ± 1.06. Maternal percentage body fat was a significant, positive predictor of milk leptin content. Milk leptin was a significant, inverse predictor of infant weight and body mass index z-scores in infants 1 year old or younger. CONCLUSION: The association between maternal body composition, milk leptin, and infant growth persists in mothers with lean body composition. Milk leptin is not associated with growth in older infants.

Too much of a good thing: evolutionary perspectives on infant formula fortification in the United States and its effects on infant health.

Recently, there has been considerable debate regarding the appropriate amount of iron fortification for commercial infant formula. Globally, there is considerable variation in formula iron content, from 4 to 12 mg iron/L. However, how much fortification is necessary is unclear. Human milk is low in iron (0.2-0.5 mg/L), with the majority of infant iron stores accumulated during gestation. Over the first few months of life, these stores are depleted in breastfeeding infants. This decline has been previously largely perceived as pathological; it may be instead an adaptive mechanism to minimize iron availability to pathogens coinciding with complementary feeding. Many of the pathogens involved in infantile illnesses require iron for growth and replication. By reducing infant iron stores at the onset of complementary feeding, infant physiology may limit its availability to these pathogens, decreasing frequency and severity of infection. This adaptive strategy for iron regulation during development is undermined by the excess dietary iron commonly found in infant formula, both the iron that can be incorporated into the body and the excess iron that will be excreted in feces. Some of this excess iron may promote the growth of pathogenic, iron requiring bacteria disrupting synergistic microflora commonly found in breastfed infants. Evolutionarily, mothers who produced milk with less iron and infants who had decreased iron stores at the time of weaning may have been more likely to survive the transition to solid foods by having limited iron available for pathogens. Contemporary fortification practices may undermine these adaptive mechanisms and increase infant illness risk.

No evidence for sex biases in milk macronutrients, energy, or breastfeeding frequency in a sample of Filipino mothers.

Maternal reproductive investment includes both the energetic costs of gestation and lactation. For most humans, the metabolic costs of lactation will exceed those of gestation. Mothers must balance reproductive investment in any single offspring against future reproductive potential. Among mammals broadly, mothers may differentially invest in offspring based on sex and maternal condition provided such differences investment influence future offspring reproductive success. For humans, there has been considerable debate if there are physiological differences in maternal investment by offspring sex. Two recent studies have suggested that milk composition differs by infant sex, with male infants receiving milk containing higher fat and energy; prior human studies have not reported sex-based differences in milk composition. This study investigates offspring sex-based differences in milk macronutrients, milk energy, and nursing frequency (per 24 h) in a sample of 103 Filipino mothers nursing infants less than 18 months of age. We found no differences in milk composition by infant sex. There were no significant differences in milk composition of mothers nursing first-born versus later-born sons or daughters or between high- and low-income mothers nursing daughters or sons. Nursing frequency also showed no significant differences by offspring sex, sex by birth order, or sex by maternal economic status. In the Cebu sample, there is no support for sex-based differences in reproductive investment during lactation as indexed by milk composition or nursing frequency. Further investigation in other populations is necessary to evaluate the potential for sex-based differences in milk composition among humans.

Predictors of breast milk macronutrient composition in Filipino mothers.

OBJECTIVES: There is increasing evidence that breastfeeding has long-term effects on offspring biology and health, which has heightened interest in understanding the extent of variation in breast milk composition and its underlying determinants. Here, we report variation in milk macronutrient composition in a well-characterized cohort of young Filipino mothers and test underlying maternal predictors of this variation. METHODS: Morning breast milk samples, anthropometrics, dietary recalls, and other interview data were collected in 102 Filipino young breastfeeding mothers (age range 24.6-25.4 years) living in Cebu City, Philippines. Milk samples were analyzed for protein, fat, sugar, and milk energy density. Regression models were used to test associations between milk macronutrient composition and maternal diet, body composition, breastfeeding duration, and feeding frequency. RESULTS: Consistent with past studies, milk fat and energy increased with duration of breastfeeding; there were no associations between maternal diet or percent body fat and milk composition with the exception of a modest, inverse association between maternal adiposity and milk sugar content. CONCLUSIONS: The relative lack of associations between maternal diet or body composition and milk composition at Cebu is consistent with past studies and suggests that milk composition may be buffered against fluctuations in maternal dietary intake or nutritional status. We speculate that the tendency for milk composition to vary between populations faced with different nutritional ecologies, but to show minimal responsiveness to intake during lactation, may enhance the reliability of milk composition as a stable intergenerational cue of typical local environmental quality.