The First 1,000 Days: Infant Health and the Gut Microbiome

Gut Health

Infant Health


Caring for one’s gut health has been rising as a wellness trend lately as more and more research highlights the way our gut microbiome health can impact our overall health. Yet, as you continue stocking up on gut-nourishing foods like kombucha, kimchi, or even probiotic supplements, did you know that it’s actually the first 1,000 days of an infant’s life that has the most influence on a person’s gut microbiome?

What Is the Gut Microbiome?

Our microbiome, aka the trillions of microorganisms found mostly in our gut, helms multiple roles, from digesting your food to ensuring optimal nutrient absorption, and even protecting you from disease-causing pathogenic microbes.

From birth, an infant’s earliest interactions with the microbial world can direct the destiny of its gut microbiome all the way into adulthood.

One major factor influencing the infant’s gut microbiome is the wellbeing of the mother. For example, if the mother is stressed, suffering from infection, or struggling with obesity, the breast milk she produces can influence the microbiome of the baby. At the same time, whether the baby has been placed on antibiotics, is breastfed, or is experiencing an infection can also affect the development of the young microbiome.

As the early colonizers of the gut get settled in, they can play a large role in a baby’s immune, gut, and brain health for the long haul. These pioneering bacteria can have an influence on a growing baby for the rest of their life. Talk about small things making a big difference! Here’s exactly how an infant’s gut microbiome can be impacted in the first 1,000 days of life.

Mode of Birth

Babies delivered vaginally are colonized with gut microbes and tend to have a higher distribution of Bifidobacterium and Bacteroides in the first three months of life. These two groups of bacteria have been noted to provide health benefits to humans.

On the other hand, an infant birthed through Cesarean section will have quite a different early gut microbiome. In particular, the baby’s initial microbiome will reflect the types of microbes found on the mother’s skin and, to a smaller extent, the surrounding delivery environment. That means there will be far less of the health-promoting Bifidobacterium and Bacteroides in its gut, an effect which has been noted to possibly increase the chance of inflammation over time.

It’s All in the Diet

Whether an infant is breastfed or formula-fed is another important factor that affects an infant’s gut microbiome. Breast milk contains indigestible sugars known as human milk oligosaccharides (HMOs) which serve as fuel for health-promoting bacteria to selectively feed on. It’s no wonder that babies who are exclusively breastfed naturally have a higher abundance of the health-promoting Bifidobacterium and Bacteroides.

On the other hand, infants exclusively fed with formula end up having higher levels of potentially pathogenic bacteria in their system, including bacterial species from ClostridiumStaphylococcusStreptococcus, and E. coli.

One type of bacteria, known as Clostridium difficile, has been shown to have a greater presence in the gut of formula-fed babies. This bacteria can cause severe diarrhea and is also responsible for colitis, a severe gut inflammatory disease.

But it doesn’t just stop at the milk or formula feeding stage—a baby’s transition to solid food is just as important in influencing their gut microbiome and eventual long-term health.

For example, the ratio of Firmicutes to Bacteroidetes (F/B) bacteria was compared between rural African children who ate a low-fat, vegetarian diet, and European children who ate a high-fat, high animal protein diet. A higher F/B ratio has been suggested to be an indicator of obesity. The study found that the European children had a higher F/B ratio than their rural African counterparts, an effect likely driven by the high-fat diet found in the European Union believed to predispose the European children to obesity.

The Gut and Early Brain Development

Our gut has a powerful influence on the brain through a connection known as the gut-brain axis. A healthy gut can lead to a healthier brain, and that’s equally true for a growing baby. In fact, the first years of life are some of the most dynamic for both the developing gut and brain—there’s growing evidence that the gut microbiota can affect cognition, and aspects of mental health like anxiety, mood, and sociability during development.

The pregnancy period is an especially important time where the gut microbiome of an infant can be impacted. Studies have shown that there exists a connection between maternal prenatal stress and levels of potentially inflammatory bacteria in the newborn. Specifically, increasing prenatal stress leads to more bad bacteria and less good bacteria in infants. Such changes in the infant’s gut microbiome are linked to increased levels of molecules that induce inflammation, some of which can negatively impact an infant’s developing brain. If there’s ever been a better reason to take it easy during pregnancy, this is it!

Further showing how gut bacteria and cognitive development are linked, a study also found that rodents born without bacteria in their gut have been shown to have poor social development and memory. However, when these animals were recolonized with the right type of bacteria found in normal rodents, these developmental issues were reversed.

Additionally, some studies have also suggested that autism spectrum disorder (ASD) may be related in part to problems associated with the type of bacteria living in the gut of babies. Factors such as maternal stress or medication use can influence the microbes passed on to the baby during birth, and the infant microbiome development onward, which may impact the neurodevelopmental challenges experienced by individuals with ASD early in life.

Good Gut Health is Priceless

The early days of the gut microbiome are some of the most critical for a baby’s life. In ensuring an increased colonization of healthy bacteria in the gut, an infant can grow up to have a reduced chance of diseases later in their adult health including the likes of inflammatory bowel disease, obesity, asthma, and allergies. Feeding an infant the necessary nutrients for promoting a healthy microbiome, such as the HMOs found in breastmilk, is key to setting the stage for good health for the first 1,000 days, and thousands more.