The first 1,000 days of life are crucial for programming future adult health and microbes play a key role in that process, constituting different microbiotas all over the body, such as on skin and in the mouth. Their presence is greatest, however, in the gut, where the gut microbiota is formed from birth and lives inside the body across the lifespan. In fact, microbes aid in both programming and training several parts of the body, including the immune system and the central nervous system.

Numerous studies have been published on the impact of factors such as nutrition in early life, mode of delivery and antibiotic intake during this critical period and for future health. With that in mind, scientists from the University of Cork (Ireland), led by Professor John Cryan at the APC Microbiome Institute, have reviewed all the scientific data available on the impact of early life nutrition on the gut microbiota and the long-lasting effects on the brain.

They conclude in an article published in the journal Nutrients that the first 1,000 days of life are a crucial developmental window. Furthermore, any alterations occurring during that period that disturb proper establishment of the gut microbiota may have long-lasting effects on the gut-brain axis.

“Understanding the link between perinatal nutrition, neurodevelopment and gut microbiota is of great importance in order to unravel the mechanisms of diseases that are believed to be rooted in early life,” state the authors in the article.

They believe that perturbations that challenge that relationship during critical temporal windows of development might disturb the gut’s internal balance and the interactions between humans and the gut microbiota, with the resulting impact on overall health.

Those perturbations can also foster structural and functional alterations in the central nervous system. In fact, examples from early life, such as high antibiotic exposure, have been linked to a higher risk of mental-health conditions such as anxiety or depression in humans.

The first key episode in this story is pregnancy. Studies have shown that some compounds produced by the maternal microbiota during pregnancy are passed on to the baby through the placenta and can influence the development and function of the baby’s central nervous system.

A balanced and diverse maternal diet notably rich in fiber is key. That, together with lifestyle, mental health, antibiotic use and environmental factors such as pollution, can affect fetal development. The question, of course, is how?

What the mother eats shapes her gut microbiota. And, in turn, the waste products or metabolites produced by the mother’s microbiota can influence the fetus’s development “with possible health outcomes on the offspring across lifespan.”

One example is prebiotic non-digestible dietary fiber, which is fermented by the gut microbiota, releasing molecules called metabolites that regulate important functions in the body. Short-chain fatty acids (SCFAs) are one such metabolite, which are absorbed into the intestine and can modulate the brain and immune system.

The next stop is birth. Previous studies have shown that the way humans come into the world affects the way microorganisms colonize us. Perinatal maternal antibiotic exposure and C-sections have been associated with the development of certain diseases later on in life, including obesity, asthma and other allergies, and type 2 diabetes.

Vaginal birth, meanwhile, promotes the main bacterial colonization of the baby’s gut. That is because, when the baby crosses the birth canal, they are impregnated with the maternal gut microbiota. That microbiota, in turn, starts colonizing the baby’s gut mainly with bacteria from the bifidobacteria family.

As for infant nutrition, bifidobacteria are also abundant in maternal breast milk. This source of nutrition is the gold standard as it provides nutrients and bioactive components such as oligosaccharides (HMO), which help modulate the immune system via the gut microbiota. Furthermore, we know that breastfeeding enhances brain development and supports the immune system in early life, while also being linked to a decreased risk of childhood obesity and type 2 diabetes.

Moving on, when solid food is introduced into the diet, some changes appear in the richness and diversity of the baby’s gut microbiota. That is when the gut microbiota begins a gradual process of diversification, with its composition stabilizing at around five years of age. The changes are crucial for the healthy development of neuronal circuits in the brain, as well as for overall health.

As can be seen, pregnancy is a key moment for the baby’s overall future health, as the mother’s gut microbiota affects the baby’s development in the uterus through the metabolites released. In addition, mode of delivery—whether a C-section or vaginal—breastfeeding and transitioning to a solid diet after weaning all modulate the child’s gut microbiota. That modulation plays a crucial role in training the immune system and enhancing brain development. So, the more diverse the child’s gut microbiota during the first five years of life, the healthier they are likely to be.



Ratsika, A.; Codagnone, M.C.; O’Mahony, S.; Stanton, C.; Cryan, J.F. Priming for Life: Early Life Nutrition and the Microbiota-Gut-Brain AxisNutrients 202113, 423.