This publication explains the importance of breastmilk to the infant gut microbiome. First, it defines the gut microbiome, then introduces the source of infant microbes, and finally, discusses the role of breastfeeding in infant gut microbiome and infant health. This publication is intended for a general audience of all educational backgrounds.
What is the gut microbiome?
Microbes live on us and in us — on our skin (Grice and Segre 2011), in our mouths (Deo and Deshmukh 2019), and even in our lungs (Whiteside et al. 2021). If you count up all the cells in the human body needed to stay healthy, the microbes will outnumber human cells (Sender et al. 2016)! The majority of these microbes live in our guts (Sender et al. 2016). The microbes living in our guts are especially important as they help our immune systems (Kau et al. 2011), brains (Galland 2014), and digestion (Banerjee et al. 2022).
Where do these microbes come from?
At birth, babies receive either vaginal microbes (in a vaginal delivery) or skin microbes (in a C-section delivery) from their mothers (Biasucci et al. 2010). These microbes form the start of the gut microbiome (Biasucci et al. 2010). But the microbes keep coming! They come from the environment (Nielsen et al. 2020), from Dad (Enav et al. 2022), from other family members (Tavalire et al. 2021), from pets (Panzer et al. 2023), and from all sorts of other places (Enav et al. 2022) to live in the baby’s gut. As a result, the number of microbes that live in a baby’s gut increases quickly during the first two or three years of life.
What does breastmilk have to do with these microbes?
Not all microbes a baby encounters are equally good. Some microbes are pathogens, meaning they can make a baby sick. Other microbes protect against serious diseases later in life, like asthma (Depner et al. 2020) or type 1 diabetes (Kostic et al. 2015). Breastmilk is important because it helps keep babies safe from pathogens (Hanson and Winberg 1972) and feeds the microbes that keep babies healthy (Bode 2012).
Credit: Adapted from National Institute of Diabetes and Digestive and Kidney Disease, National Institutes of Health
Breastmilk is made of many different things. The four most abundant things in breastmilk are water, lactose (a sugar the baby can digest), fat, and human milk oligosaccharides (HMOs) (Petherick 2010). HMOs are specialized sugars that the baby cannot digest. However, some microbes can eat them — especially microbes that are important to a baby’s health! A group of microbes called Bifidobacterium is particularly likely to eat HMOs (Underwood et al. 2015). Bifidobacterium is important because babies who have lots of these microbes in their guts are less likely to have asthma (Seppo et al. 2021) or type 1 diabetes (Insel and Knip 2018) later in life. Breastmilk is not just food for babies; breastmilk also feeds the microbes that help keep babies healthy. Only a few formulas contain any HMOs, and the HMOs in these formulas are at lower levels than those found in breastmilk. So, to feed your baby and your baby’s microbes, breastmilk is the most nutritious option!
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