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8 Biggest Factors Affecting the Microbiome

Now that we have covered what the microbiome actually is and what it does for our health, it’s time to discuss how we can modify the growth of the "good" vs. the "bad."

In utero, an infant was originally thought to have a sterile GI tract. Recent evidence suggests that they may have low levels of bacteria from mother’s placenta and amniotic fluid. However, the major colonization event of the GI tract happens during birth and continues until age ~2-3 years old.

1. Birth Method

How we come into the world is very important for the future health of the microbiome! Each method results in completely different species colonizing the GI tract of the infant, which has implications for future health.

Vaginal birth: Mother’s vaginal, skin, and rectal microflora inoculate baby

Caesarean section: Baby is inoculated with bacteria from hospital environment and abdominal skin

Given the association between babies born C-section and increased health risks (like obesity, Type 1 Diabetes, etc.) later in life, some progressive centres are swabbing a baby’s mouth with vaginal sample from mother if born by C-section.

2. Breast feeding

It’s recently been discovered that during the third trimester, dendritic/macrophages (cells of the immune system) travel from mother’s breast tissue to small intestine via lymphatic system to pick up bacteria and bring back to breast tissue so that it becomes incorporated in breast milk. These bacteria help with early colonization of infant’s GI tract before it’s even born! When a baby breastfeeds, it receives the bacteria from its mother’s skin in addition to these recruited bacteria in the milk.

Formulas are starting to include probiotics, but products back in the day certainly didn’t! There was a phase (that affected many baby boomers) where breast feeding was looked down on and formulas were considered the ‘high class’ option.

This is a whole topic in itself but to simplify, breastfeeding for an adequate length of time is important for baby’s future immunological health. Current guidelines recommend at least 1 year of breastfeeding.

3. Environment

Urban vs. rural up-bringing, local pollution, pesticide load, presence of pets in the home, cleanliness of home, time spent outside, presence of siblings – all affect early colonization of the microbiome. Basically, the more exposure at an early age to others, the outdoors, and bugs – the better!

Ex. A Swedish study found that kids who grew up in a house a dishwasher, had lower rates of allergic disease later in life.

This finding (and there are hundreds of other examples) supports the idea of the Hygiene Hypothesis (HH). The basis of HH is that as a society, we have become hyper-vigilent on cleanliness and our exposure to dirt, bacteria, germs, etc. has been greatly reduced. Normally, these encounters pose challenges for the maturing immune system, which is required for normal immune development. It’s one of the theories behind the recent rise in autoimmunity and cancer: too clean=lack of immune development from an early age so we have exaggerated responses to things as we age.