Yesterday I blogged about the importance of gut microbes, and recent news showing that birth mode (vaginal vs c-section) and infant feeding (breastmilk vs formula) affect babies’ development of good bacteria for long term health. Today there’s another piece about this in the Times. The article covers a Canadian study which found, again, that babies born by c-section and those who don’t have a breast milk diet have less protective gut bacteria at four months old, and more of the harmful germs that make you sick. The authors of the study believe that this is a pathway for various autoimmune problems in older people.

You can read the full study here. I don’t love this study because the total number of infants is low. More importantly, it, like so many studies that start to examine the nursing relationship, doesn’t really clarify what “breastfeeding” means. They differentiate “formula feeding” from “exclusive breastfeeding” and “partial breastfeeding” at the time they took the samples, but there’s no apparent guidance about how to use those terms. My concern is that without good definitions, we can’t properly interpret the results. For instance: if a baby was given one bottle of formula on day 1 in the hospital (as so many are) but went on to have nothing but breast milk for the next many months, is that baby “exclusively” or “partially” breastfed? If we are looking at the effect of early exposure to nonnatural microbes, it seems wrong to compare that baby to one who has had nothing but breast milk from birth. But if we are looking at whether a protective effect of breast milk is dose-dependent, it seems wrong to lump that baby in as “partially” breastfed with another who has had half breast milk and half formula for four months. These distinctions are rarely made in studies that purport to look at the ways infant feeding affects health outcomes. But if we’re going to learn anything real, we need to look closely at what it is we’re trying to study. “Breastfeeding” isn’t just one thing.