Underlying human milk is a complex biological system, consisting of a matrix of many interacting parts.  As such, human milk is best studied as an ecology consisting of inputs from the lactating parent, their breastfed baby, and their respective environments.

In response, in 2020, the National Institute of Child Health and Human Development (NICHD) launched the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project, with a mission to explore all the factors underlying the synthesis, composition, and most effective use of human milk.  The BEGIN Project represents a shift away from an exclusive focus on human milk as a delivery system of individual components to a more expansive view of human milk as a complex ecological system influenced by various environmental inputs.

The five Working Groups of the BEGIN Project were established to address:

  1. Parental inputs to human milk production and composition
  2. Components of human milk and the interactions of those components within the complex ecological system of lactation and breastfeeding
  3. Bi-directional relationships associated with the breastfeeding dyad
  4. Application of technologies and methodologies to study human milk as a complex ecological system
  5. Leveraging new discoveries to support safe and efficacious infant feeding practices

This Supplement is open access: readers may access all the articles regardless of subscription status.

The current findings of each of the five Working Groups, along with an executive summary, have been published in a May 2023 Supplement to The American Journal of Clinical Nutrition (AJCN).  This Supplement, Breastmilk Ecology: Genesis of Infant Nutrition: BEGIN Project, is open access so that all readers regardless of subscription status may access all the articles at no charge.  Below is a quick overview of each of the Working Group’s findings:

Parental Factors That Impact the Ecology of Human Mammary Development, Milk Secretion, and Milk Composition—A Report from Breastmilk Ecology and the Genesis of Infant Nutrition (BEGIN) Working Group 1

“We are at the early stages in understanding the systems biology of human milk and lactation,” according to ASN member Margaret C. Neville et al.  Among the many issues explored by the authors is the effect of medications, recreational and illicit drugs, pesticides, and endocrine disrupting chemicals on milk secretion and composition, an area that the authors believe is in need of more research attention.  The authors also examined how parental and environmental inputs that affect lactation and milk composition are affected by depression, anxiety, and psychosocial stress.  Moreover, the authors point out that experiences of racial discrimination and economic hardships, which are linked to physiological stress, remain severely understudied in relation to lactation. In response, the authors have underscored that “diversification of our study populations to include families of color and lower income families is critical.”

Ecologies, Synergies, and Biological Systems Shaping Human Milk Composition—A Report from Breastmilk Ecology and the Genesis of Infant Nutrition (BEGIN) Working Group 2

The components of human milk tend to be studied in isolation, even though there is reason to believe they interact with each other.  In addition, milk composition can vary greatly both within an individual as well as within and among populations.  In response, Jennifer T. Smilowitz et al. have explored the factors underlying variations in human milk composition.  Specifically, the authors looked at how human milk’s components interact to nourish, protect, and communicate complex information to a breastfeeding infant.  The authors believe that “multi-disciplinary research teams will need to fully collaborate to elucidate how milk acts as a biological system.”  Moreover, “the complexity of human milk composition will require highly sensitive, comprehensive methodologies involving a ‘multi-omics’ approach.”

Infant Factors that Impact the Ecology of Human Milk Secretion and Composition—A Report from Breastmilk Ecology and the Genesis of Infant Nutrition (BEGIN) Working Group 3

Far from being a passive recipient, the infant drives many lactation processes and contributes to the changing composition of human milk via multiple mechanisms, including the infant’s innate genetic and phenotypic make-up.  In this article, Kevin Jarvis et al. address milk removal (i.e., the transfer of human milk to infant); the infant’s effect on the composition of human milk ecology; and the impact of disruptions in gestation on the ecology of fetal and infant phenotypes, milk composition, and lactation.  Moreover, the authors explore the chemosensory ecology for the parental-infant dyad, including how infants detect flavor changes in human milk resulting from parental lifestyle choices such as recreational drug use.  The authors demonstrate how “early experiences with the sensory properties of these recreational drugs impact subsequent behavioral responses.”

Evidence for Human Milk as a Biological System and Recommendations for Study Design—A Report from Breastmilk Ecology and the Genesis of Infant Nutrition (BEGIN) Working Group 4

Previous research studies have compared human milk to infant formula, an approach that has provided some insight into the bioactivity of both individual human milk components and human milk as a whole.  ASN member Sharon M. Donovan et al., however, believe that “this experimental approach cannot capture the contributions of the individual components to the human milk ecology, the interaction between these components within the human milk matrix, or the significance of the matrix itself to enhance human milk bioactivity on outcomes of interest.”  In response, the authors present new approaches that explore human milk as a biological system and the functional implications of that system and its components. More specifically, the authors discuss study design and data collection considerations as well as the application of emerging analytical technologies, bioinformatics, and systems biology approaches.

An Equitable, Community-engaged Translational Framework for Science in Human Lactation and Infant Feeding—A Report from Breastmilk Ecology and the Genesis of Infant Nutrition (BEGIN) Working Group 5

Human milk is the ideal source of nutrition for most infants, but significant knowledge gaps remain in our understanding of human milk biology.  In order to optimize the application of new discoveries and knowledge across all stages of human milk research, ASN member Laurie Nommsen-Rivers et al. have developed a translational framework for science in human lactation and infant feeding.  To demonstrate the application of their newly devised translational research framework and its overarching principles, the authors present six case studies, each illustrating research gaps across all stages of human lactation and infant feeding.  According to the authors, “applying a translational framework approach to addressing gaps in the science of human milk feeding is an important step toward the aligned goals of optimizing infant feeding across diverse contexts as well as optimizing health for all.”

We invite you to explore this important AJCN Supplement in its entirety to gain a deeper understanding of breastmilk ecology as well as to learn where more research is needed.