Building your microbiome where did it go wrong?

The human microbiome is a complex ecosystem of bacteria, viruses, and fungi living in and on the body. Far from being passive passengers, these microbes actively shape immunity, digestion, metabolism, and even brain development. Understanding how this forms and what disrupts it is a critical area to understand to improve your health. Being able to pinpoint the areas which were affected during development really helps you target treatment as a practitioner to address the underlying causes.

If you are a new Mum and reading this blog or a parent concerned that a choice has resulted in damage be comforted by the fact that this is largely recoverable and you can always support the gut to return to more optimal levels of gut health. I say this because there are too many things that parents are made to feel guilty about and I genuinely think this should not be one of them.

You arrive in the world carrying almost no bacteria. Within hours, trillions of microorganisms begin colonising your gut, skin, and airways community they building an environment that will support your health over the next few years.

Before Birth

The womb was long thought to be sterile, but we now know that prenatal factors begin shaping the microbiome before birth even occurs. The mother's gut and vaginal microbiome change significantly during pregnancy. The vaginal microbiome, in particular, shifts toward Lactobacillus dominance in the third trimester, preparing for the microbial handover that will happen during delivery.

Birth: The big gift at the start !

Birth can be the most dramatic microbial event of a person's life, not to mention a dramatic event in Mum’s life too! How it happens can have significant impacts on your microbiome.

Vaginal birth sees an innoculation with Mum’s bacteria which can rapidly colonise the newborn gut and begin priming the immune system.This is specially the case for Lactobacillus and Bifidobacterium species.

Infants born by C section miss this exposure. Their first microbial contacts tend to be environmental: skin, air, and hospital surfaces. These babies typically show lower levels of beneficial Bifidobacterium and higher levels of hospital-associated species.

These differences can persist beyond the first year and are associated with increased risk of allergic disease, asthma, and obesity — making delivery mode one of the strongest determinants of early microbiome composition.

Feeding: The Next Great Shaper

After birth, nutrition becomes the dominant force in microbiome development.

Breast milk is an amazing food. It contains live bacteria, immune proteins, and human milk oligosaccharides (HMOs) — complex sugars that the infant cannot digest but that selectively feed beneficial gut bacteria, especially Bifidobacterium infantis. Breastfed infants develop microbiomes heavily dominated by Bifidobacterium, producing metabolites that lower gut pH, inhibit pathogens, and regulate immune responses. Formula-fed infants develop a more diverse, less Bifidobacterium-dominant community, though modern formulas incorporating HMOs and prebiotics have narrowed this gap considerably.

The other benefit of breastfeeding is that the HMO’s in breast milk appear to crowd out less beneficial species like Streptococcus, Enterococcus and Clostroides. There are probiotics on the market that can be used to provide HMO’s and other useful species like Bifidobacterium infantis if you are seeing more infections in a baby than normal.

The introduction of solid foods around four to six months marks the next inflection point. As dietary complexity grows, microbial diversity expands. By around age three, the microbiome broadly resembles that of an adult and remains relatively stable thereafter. The introduction of solid foods with reasonable variety as the baby grows is another useful strategy to build diversity in the gut flora.

Key Factors That Shape Development

Beyond delivery and feeding, several other factors powerfully influence how the microbiome forms:

Antibiotics. Perinatal or early-life antibiotic exposure significantly disrupts microbial diversity, depleting beneficial taxa like Bifidobacterium. Even a single course in infancy can alter the microbiome for months. Repeated exposure compounds these effects and has been linked to increased risk of inflammatory bowel disease, allergies, and metabolic dysfunction — underscoring the importance of careful prescribing in young children.

Environment. Children raised on farms, in rural settings, or with pets develop more diverse, resilient microbiomes. Greater exposure to environmental microorganisms through soil, animals, and outdoor play appears genuinely protective — consistent with the idea that the human immune system evolved alongside rich microbial exposure.

Maternal diet and stress. What a mother eats during pregnancy and breastfeeding shapes the microbial composition of breast milk and the infant gut. Diets rich in fibre and plant diversity support more favourable microbial profiles. Chronic stress, meanwhile, can alter the maternal gut microbiome and inflammatory environment, with downstream effects on the offspring's microbial development.

Why It Matters

The stakes of early microbiome disruption are significant. Disturbed microbial development in the first three years of life has been associated with increased risk of:

• Allergic diseases, including eczema, food allergy, and asthma

• Inflammatory bowel disease

• Obesity and metabolic dysfunction

• Neurodevelopmental and mental health conditions, via the gut-brain axis

• Autoimmune disease

Whilst none of these conditions is trivial a well rounded diet and appropriate choice of prebiotics and probiotics can have a big impact on reducing risk and improving symptoms. Appropriate testing of the gut microbiome can also be a really helpful way to identify what treatment is needed and ensure targetted support.

Looking Ahead

The early microbiome is not destiny. Research is actively exploring ways to support healthy development — from vaginal microbiome seeding for CS-born infants, to targeted probiotics and prebiotics, to dietary guidance during pregnancy and infancy. The science is moving quickly, and the window of early life represents a genuine opportunity to intervene before long-term health trajectories are set.

We are, in a very real sense, shaped by the microbes we meet in our earliest days. Understanding that relationship may be one of the most powerful tools we have for building healthier lives from the very beginning.