What role do gut bacteria play in digestion? Health insights

Heather Campbell
 min read

What role do gut bacteria play in digestion?

What role do gut bacteria play in digestion? Health insightsBacteria are present in our small intestine but especially in our colon as the main component of their microbiota.

As a whole, there are about a thousand species of bacteria in the colonic microbiota and each of us has our own unique microbiotic identity.  They are essential to our vital functions, and therefore, quite simply, essential to life itself.

The colon is the preferred place for bacteria, it is their main habitat not only in quantitative but also qualitative terms, so we’ll focus on that.

The population that bacteria constitute is characterized by the high number of its members and their great biodiversity and the multiplicity and variety of the functionalities in which they actively participate.

Read on to learn where bacteria come from, how they colonize our bellies and what roles they play…

What role do gut bacteria play in digestion? The introduction of bacteria in the belly

For 9 months, embryo then fetus, you enjoyed the warmth of your mother’s womb.

You were protected from the outside world while being cradled and massaged to the rhythm of her breathing. It was she who fed you with the products of her digestion and protected you with her immunity.

You were growing on her hormones. The environment in which you were developing and your developing digestive tract were, without doubt, sterile.

Again, the lack of bony protection on the anterior aspect of the maternal abdomen allowed tactile contact between you and her. She felt you and lived with you.

You left this cocoon at the end of the pregnancy. Then, as a newborn, you left a closed universe (the uterus) where oxygen was scarce, to be propelled into an oxygenated world.

That’s when you took your first breath.

It was at the same time that, during the birth and in the moments that followed, you left a sterile cocoon and entered a universe that was not.

That’s when the bacteria became your vital partners and never left you again.

The origin, composition, and therefore the functionality of your newborn microbiota are influenced by your mother’s lifestyle, diet, and environment and the type of delivery (natural, cesarean or preterm).

A natural vaginal birth guarantees the ideal installation of bacteria.

Hundreds of billions of bacteria were already present after a few days, because of the very high speed of multiplication of bacteria (a single bacterium can have 295 million descendants in 1 day).

As for your digestive tract, while it was not, or hardly, operational at the fetal stage, its heavy task was to take over from your mother for your nutrition and your defenses against external risks, whether chemical or microbial.

In the process of responding to these challenges, a multitude of bacteria has taken up residence in your belly.

Their first function was to immediately start the secretion of mucus that forms the viscous inner surface of your small intestine and your colon and contributes to their sealing, and also to the development of your immune system.

But progressively they have also participated in a multitude of other vital functions, including hormonal and cerebral.

Without this implementation and the multiple functionalities that come with it, your life would not have been possible in the real world.

The microbiota of the colon is exceptional

The other microbiota of our body (skin, ear canal, upper respiratory tract, vagina, etc.) are important, they recognize each other, communicate and interact.

So the microbiota of our colon is exceptional in more ways than one. We have come to understand that gut bacteria and digestion are intertwined to an incredible degree.

It has the largest and most diverse population of bacteria in the world, providing opportunities to perform and contribute to a multitude of functions.

Bacteria are also present in our small intestine and play several roles there, notably in the development of our immune system.

However, the bacteria are quantitatively much less numerous. Their composition and diversity are simpler and the functionalities they contribute to are more limited.

In addition, the food bolus transits at high speed and therefore stays there for a short time and is also more difficult to access for study.

Indeed, if the analysis of our fecal microbiota (the only one that is easily accessible) allows us to have a reasonable knowledge of the composition of the colonic microbiota, it is not the same for that of our small intestine.

The life of bacteria in the human belly

After birth, the implantation of bacteria in our womb continues and the bacterial diversity increases from the bacteria in the colostrum, then in the milk, mouth, breasts and skin of our mother, but also from the influence of our genetic heritage.

These bacteria quickly become, quantitatively and functionally, mainly colonic even if they persist in all digestive segments.

During this first period of our lives, bifidobacteria (the bacteria in bifidus yogurt) are generally dominant because breast milk contains selective food factors that promote their growth.

These influences, which are decisive in the first months of our lives, diminish fairly quickly to make room for the environmental and dietary factors to which we are exposed during childhood as well as our own vitality.

At the age of 2 or 3, the composition of our colonic microbiota has stabilized. It has reached a functionally stable state that persists, at least, throughout the adult period.

Related post: What can cause an imbalance in gut flora populations?

The composition of our colonic microbiota

In general, the composition of colonic microbiota differs from that of communities present at other sites in our body.

But it also differs from those of other living beings. It is a specialized community of bacteria capable of thriving in our belly’s warm, anaerobic and stable environment.

In adult life, in a Western-type colonic microbiota, the bacteria are tens of thousands of billions of individuals belonging to several hundred species for a total weight of a few hundred grams.

On a body scale, this represents 55 to 88% of all our cells and 1.5 to 3.5% of our total body mass. Bacteria find shelter and food in these conditions of life. This biodiversity can evolve and tend to be reduced as we age.

Each person has a unique microbiotic fingerprint

The composition of our colonic microbiota has a certain individual character.

Indeed, we create a personal link with it (genetic and/or immune) that generates a kind of microbiotic imprint that seems to remain relatively stable over time.

Only external events can change it. Some examples:

  • Major changes in your health (for example, if you become obese) or quality of life
  • Chronic exposure to toxic substances
  • Prolonged or repeated antibiotic treatments
  • New eating practices that are established over time (e.g. becoming vegetarian)

In the lumen of our colon our bacteria circulate freely. They live there either solitary or grouped in colonies.

Many are also adsorbed on different solid matrices such as dietary fibers or waste from our cells. So gut bacteria and digestion go hand in hand in working well.

A significant portion of them also settles in the mucus, the viscous secretions that line our epithelia. As these have different chemical characteristics depending on their location, each area hosts different species.

Those that live in this environment establish very close contacts with the cells of our intestines.

They allow the reception and transmission of signals whose origin and range go beyond the limits of these organs. They diffuse throughout our bodies. Some can even reach our brains.

Bacteria talk about their microbiome

Like all living beings, we have genes that together constitute our microbiome.

Our own genome with all eukaryotic body cells contains more than 20,000 genes. But in our colonic microbiome there are several million non-redundant ones. And that’s a few hundred times more.

The presence of bacteria provides us with almost 99% of all our genes at our disposal. Genetically we are, in a way, more bacterial than mammalian.

Many of these genes correspond to molecules (metabolites) that may be necessary for our body to function. The number of these molecules, produced by our bacteria, could reach up to 40% of all those that are active in our body.

As microbiota, bacteria act as the most complex signaling system capable of influencing our cells, including those of our brain.

What role do gut bacteria play in digestion? Conclusion

The digestive tract of our developing fetus as well as the environment in which it has developed are classically considered sterile.

Therefore, at the end of gestation, during childbirth and in the moments following it, a microbiota settles in our digestive tract and there gut bacteria and digestion become essentially linked.

This bacterial population then grows and diversifies. It is in our colon that most of its implantation takes place very quickly.

Its origin is to be found in our mother’s fecal, vaginal and skin microbiota, but also in the environment in which we live and then in our diet. Relatively simple in the first days of our life, this population becomes more complex afterward.

Our birth was a very important moment for our belly. With the installation of bacteria in our colon, they have begun their indispensable contributions to its functioning and to our vitality.

We can now describe the fecal component of our microbiota (those of the small intestine and the colon being difficult to access) and compare it to that of other individuals and other populations.

In the human species as a whole, there are about a thousand species of bacteria in the colonic microbiota.

However, this number is a few hundred at the individual level, divided between dominant, subdominant and minority.

The composition of the dominant component is stable and individualized (our microbiotic footprint). It is more unstable and variable in the subdominant and minority fractions.

These bacteria are not completely floating in the lumen of our colon. Some are partially associated with the mucus that covers its epithelium or adsorbed on solid matrices that circulate in it.

Related postWhat are the consequences of imbalance of intestinal microflora?

About Heather Campbell

As a nutritionist, my field of specialization is science-based nutritional advice but more importantly, it is my goal to share capturing and inspiring stories, examples and solutions which can help plus-size individuals overcome their specific difficulties. Read More