Tiny Health Baby Gut Types: What Every Parent Should Know

A newborn baby sleeping peacefully, symbolizing early life stages when the infant gut microbiome begins to develop


  • Tiny Health Baby Gut Type gives you a unique perspective and understanding of your baby's gut development within their first year.
  • If your baby doesn’t have an optimal Baby Gut Type, the good news is that baby gut types are modifiable and there’s plenty of room for improvement.
  • Two key events help determine which Baby Gut Type your baby has: vaginal or C-section birth and how your baby is fed.
Our gut health report gives you deep insights into your baby's gut health. See a sample
Our gut health report gives you deep insights into your baby's gut health. See a sample

What are Baby Gut Types, and what can you expect to see?

At Tiny Health, we developed seven Baby Gut Types to simplify the way we talk about the baby gut microbiome. Each gut type gives you a unique perspective and understanding of your baby's gut development within their first year.

Illustration depicting Tiny Health's 7 baby gut types for infants aged 0 to 8 months
For babies 0 to 8 months of age

Illustration depicting Tiny Health's 7 baby gut types for infants aged 9 to 12 months
For babies 9 to 12 months of age

A plot depicting a baby's gut type at various ages, showing how it changes over time.
Thanks to different interventions recommended in the action plan, a non-ideal Baby Gut Type can transition to an ideal type

Take Note: Tiny Health Baby Gut Subtypes A and B

Each one of these seven Baby Gut Types can further be subdivided into A or B subtypes. This will depend on the level of protective Bifidobacterium present in your baby’s gut.

  • Subtype A: medium or high Bifidobacterium.
  • Subtype B: low Bifidobacterium.

For example, if your baby is Type 2A, it means that the dominant bacteria in their gut are Bacteroidaceae but Bifidobacterium are present at a healthy level.

On the other hand, if your baby is Type 4B, they mostly have Enterococcus and low Bifidobacterium. Which is when we would suggest a little extra support.

What are the different Tiny Health Baby Gut Types?

Baby Gut Type 1 - Bifidobacterium-dominated

A plot depicting Tiny Health's baby gut type 1: Bifidobacterium-dominated

Bifidobacterium are friendly bacteria associated with good health. So ideally, they’re present in the baby’s gut from birth onward, although we would expect higher levels in babies and children under the age of three.

In many ways, Bifidobacterium are your baby’s best friends. For example, they:

  • Produce lactate and short-chain fatty acids (SCFAs) like acetate when they digest human milk oligosaccharides (HMOs), which makes it hard for unfriendly gut bacteria to survive [1]
  • Play an important role in educating your baby’s immune system [2]–[5]
  • Promote the presence of a healthy microbiome by supporting the growth of other Bifidobacterium [2], [6]
  • Provide nutrition, by synthesizing essential micronutrients, such as vitamins B12, B6, folate, and vitamin K [7]

Baby Gut Type 1 is linked to a vaginal birth with few medical interventions and breastfeeding. As it turns out, breastfeeding has a significant impact on the development of Bifidobacterium. Within a couple of weeks of breastfeeding, a baby born via C-section can have comparable levels of Bifidobacterium as a baby born vaginally [8].

As long as your baby is breastfed, Bifidobacterium will generally remain high in your baby’s gut during their first 6 months of life [9]. This is important because low levels of Bifidobacterium in babies are linked to chronic diseases, including autoimmunity, asthma, and obesity [10]–[12].

Baby Gut Type 1 is linked to a vaginal birth with few medical interventions and breastfeeding. As it turns out, breastfeeding has a significant impact on the development of Bifidobacterium. Within a couple of weeks of breastfeeding, a baby born via C-section can have comparable levels of Bifidobacterium as a baby born vaginally [8].

Baby Gut Type 2 - Bacteroidaceae-dominated

A plot depicting Tiny Health's baby gut type 2: Bacteroidaceae-dominated

Bacteroidaceae are generally friendly gut bacteria and they’re found in almost all people.

Some species of Bacteroidaceae can degrade some of the sugars in breastmilk (HMOs) which is good for your baby [13]. That said, they may not be as efficient as Bifidobacterium in breaking down all types of HMOs [14]. A Bacteroidaceae-dominant baby gut is linked to vaginal births, especially home births [14], and may help prepare your baby’s gut for the introduction of solid food [15], [16].

Together with Bifidobacterium, Bacteroidaceae play a major role in the early gut microbiome.

It is important to note that Bacteroides are absent in almost all babies born by C-section delivery[17] and are particularly affected by antibiotics given to the mom either before or during labor[18], [19]. If it’s an option for you, we advocate for an antibiotic-free vaginal birth so that your baby’s gut can shelter the best bacteria possible.

Baby Gut Type 3 - Enterobacteriaceae-dominated

A plot depicting Tiny Health's baby gut type 3: Enterobacteriaceae-dominated

Enterobacteriaceae are bacteria found almost everywhere in nature, including the baby’s gut. But this doesn’t mean we want to see this family of bacteria dominating the baby’s gut.

Some species are friendly and even desired in the newborn gut [12]. However, at high enough levels, some Enterobacteriaceae can cause serious problems due to their pro-inflammatory properties [20]. For example, Klebsiella species were associated with the development of a higher incidence of respiratory infection later in life [21].

Many Enterobacteriaceae species often carry genes related to antibiotic resistance that allow them to survive exposure to antibiotics designed to kill bacteria [22], [23], and are particularly dangerous in premature babies [24]. 

Because Enterobacteriaceae are common members of the hospital environment, this gut type is frequently seen in C-section born babies, vaginal hospital births, and babies born prematurely, who often have to spend extensive time in the hospital.

Baby Gut Type 4 - Enterococcus-dominated

A plot depicting Tiny Health's baby gut type 4: Enterococcus-dominated

Baby Gut Type 4 is dominated by enterococci. Some species of Enterococcus can swing both ways, making them both friendly and unfriendly [25]. Either way, if this bacteria dominates your baby’s gut, it’s likely not ideal.

Baby Gut Type 4 is linked to both vaginal and C-section births [21]. The presence of Enterococcus faecalis in babies has been associated with respiratory infections [21] and E. faecalis is more likely than other bacteria to carry genes related to antibiotic resistance [26].

When these unfriendly species dominate your baby’s microbiome, you may want to consider decreasing E. faecalis levels and increasing the levels of beneficial Bifidobacterium.

This is not a very common gut type.

Baby Gut Type 5 - Streptococcus-dominated

A plot depicting Tiny Health's baby gut type 5: Streptococcus-dominated

Baby Gut Type 5 is dominated by streptococci bacteria. Streptococci are mostly found in the mouth, stomach, and small intestine of healthy people.

They can be a small part of a healthy early-life microbiome community but are not ideal to have as a dominant baby gut type. Some Streptococcus may increase the risk for eczema [27] and type I diabetes [28]. However, more data is needed to determine if these relationships are causal.

This is not a very common gut type.

Baby Gut Type 6 - Staphylococcus-dominated

A plot depicting Tiny Health's baby gut type 6: Staphylococcus-dominated

Staphylococcus is mostly found on the skin and is not adapted to live in the baby or adult gut.

But these bacteria are sometimes found to colonize the gut of babies born through C-section delivery [19], [29]. High levels of staphylococci define Baby Gut Type 6. It’s important to note that we expect Staphylococcus to decrease quickly throughout the first months of life as it is outcompeted by other species that are better adapted to living in the gut [28], [30].

Colonization of newborn babies with Staphylococcus aureus may increase the risk of infection in early life [31] and the presence of S. aureus in the nose of children has been associated with asthma [32]–[34]. While we’ll keep you updated as more research becomes available, it’s clear that you do not want Staphylococcus to be dominant in your baby's gut.

This is not a very common gut type.

Baby Gut Type 7 - Other

A plot depicting Tiny Health's baby gut type 7: Other

Sometimes a baby's gut microbiome does not fit into any of the six Baby Gut Types that we defined. If your baby is type 7 that means that a high percentage of the bacteria present in their gut are species that we don’t normally see dominating the baby’s gut.

Before 6 months, this is quite rare and is usually linked to a C-section birth, vaginal birth with medical interventions, or formula-feeding [18], [35], [36]. 

If your baby is 6 months or older and Type 7, don’t be alarmed. This Baby Gut Type is a sign that the microbiome has started to diversify. It may be normal if your baby has started solids or weaned from breastmilk, which can take place between 6-9 months.

Take note: You can change your baby’s gut type

A baby’s gut microbiome is highly malleable and continues to develop and change throughout the first 3-5 years of your baby’s life. Discover your baby's gut type and ensure their optimal development with Tiny Health's Baby Gut Health Test.

The optimal Tiny Health Baby Gut Type is the one that gives your baby the best start by providing them with health-promoting microbes, such as Bifidobacterium. If it’s available to you, continue breastfeeding your baby to maintain or increase Bifidobacterium levels. 

If you need to increase Bifidobacterium levels in your baby’s gut but breastfeeding isn’t an option, you can consider supplementing with the right kind of probiotics for your baby or using a formula with HMO prebiotics.

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Take a look inside our baby gut health report

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