Therapeutic food interventions have reduced mortality in children with severe acute malnutrition (SAM) but incomplete restoration of healthy growth remains a major problem1,2. The relationships between the type of nutritional intervention, the gut microbiota, and therapeutic responses are unclear. In the current study, bacterial species whose proportional representation define a healthy gut microbiota as it assembles during the first two postnatal years were identified by applying a machine-learning-based approach to 16S rRNA datasets generated from monthly fecal samples obtained from a birth-cohort of children, living in an urban slum of Dhaka, Bangladesh, who exhibited consistently healthy growth. These age-discriminatory bacterial species were incorporated into a model that computes a ‘relative microbiota maturity index’ and ‘microbiota-for-age Z-score’ that compare development (defined here as maturation) of a child’s fecal microbiota relative to healthy children of similar chronologic age. The model was applied to twins and triplets (to test for associations of these indices with genetic and environmental factors including diarrhea), children with SAM enrolled in a randomized trial of two food interventions, and children with moderate acute malnutrition. Our results indicate that SAM is associated with significant relative microbiota immaturity that is only partially ameliorated following two widely used nutritional interventions. Immaturity is also evident in less severe forms of malnutrition and correlates with anthropometric measurements. Microbiota maturity indices provide a microbial measure of human postnatal development, a way of classifying malnourished states, and a parameter for judging therapeutic efficacy. More prolonged interventions with existing or new therapeutic foods and/or addition of gut microbes may be needed to achieve enduring repair of gut microbiota immaturity in childhood malnutrition and improve clinical outcomes.

We describe the need to further integrate the fields of human microbial ecology and anthropology and outline some of the potential goals and benefits of this collaborative work.food | human microbiome | integration of natural and social sciences | subfields of anthropology

Microbiome science asserts humans are made up of more microbial cells and genes than human ones, and that each person harbors their own unique microbial population. Human microbiome studies gesture toward the post-racial aspirations of personalized medicine—characterizing states of human health and illness microbially. By viewing humans as “supraorganisms” made up of millions of microbial partners, some microbiome science seems to disrupt binding historical categories often grounded in racist biology, allowing interspeciality to supersede race. But inevitably, unexamined categories of race and ethnicity surface in a myriad of studies on microbiota. This paper approaches race as a ghost variable across microbiome research and asks, what is race doing in studies of the microbiome? Why is it there, and how is it functioning? I examine this research to argue that social scientists must work with biological scientists to help put microbial differences into perspective—to investigate how microbiomes and race are entangled embodiments of the social, environmental, and biological. Ultimately, transdisciplinary collaboration is required to address racial health disparities in microbiome research without reifying race as a straightforward biological or social designation.

Humans are inextricably linked to each other and our natural world, and microorganisms lie at the nexus of those interactions. Microorganisms form genetically flexible, taxonomically diverse, and biochemically rich communities, i.e., microbiomes that are integral to the health and development of macroorganisms, societies, and ecosystems.