Illustration by Colin JohnsonOld assumptions about human breast milk are giving way to new thinking about microbes in milk and their role in children’s health and our immune systems.

It happened again, most recently at a conference in Prague. After she gave her talk, a scientist came up to Shelley McGuire, a pioneer exploring the microbial communities found in human breast milk, and told her, You don’t know how to take a sample. Your samples must have been contaminated. Human milk is sterile.

McGuire, a professor of human nutrition at Washington State University, knows differently: She’s seen the microbes with her own eyes. But she understands the shock some feel when long-held assumptions are challenged. The realization that our health and well-being depend on vast communities of microbes hanging out in our most intimate areas has been something of an eye opener for a lot of researchers.

“It’s like a whole new world,” McGuire says.

Microbial communities—microbiomes—are everywhere. They are in our mouths, eyes, gastrointestinal tracts, and sex organs. Microbes cover our skin, swarm through air and water, and invest our soils with life-giving properties that feed the plants that feed us. Our gut microbes help us extract nutrients from our food, protect us from disease, and probably affect our moods and immune systems. Microbial communities in soil are plants’ metabolic partners and, as well, are able to sequester toxic metals and other materials, keeping them out of our food supply. Microbiota in air and water, meanwhile, perform critical environmental services that researchers are only now beginning to understand.

Read the full story in Washington State Magazine >>