Surprise! Babies Are Born With “Dirty” Guts

Babies are cute, cuddly bags of bacteria, from a microbial point of view. And scientists say that’s natural! It’s also surprising.

New studies have turned previous scientific theories on their heads. Doctors had thought the fetus rested pure and clean in the womb. A baby got his first gut bacteria during the mess we call birth, the theory went.

But now it’s been shown that bacteria invade the gut of the fetus. University of Spain researchers found bacteria that help create lactic acid in the guts of 20 fetuses in 20 different women. They found that a pregnant mother’s habits – smoking, eating organic food – influenced the types of microbiomes the fetus developed.


When the Spanish team presented their findings last month, scientists reacted with excitement to the possibility that a mother could influence her unborn child’s microbiomes. Some microbiomes are linked to good health, and others to obesity and eczema. The possibility that a mother could pass microbiomes to her unborn child that will enhance the baby’s health will require further study.

Canadian scientists are examining whether microbiomes can affect a baby’s personality. At McMaster University, researchers found that mice bred in sterile environments, with no bacteria, were overly aggressive. Once they were given a certain strain of bacteria, they behaved normally.