Our bodies teem with bacteria — in our mouths, our intestines, the birth canal, even our skin.
In fact, there are as many bacteria residing in our bodies as actual cells comprising our bodies (source). So it's no wonder that the size, type, and diversity of our own bacterial colonies play a larger role in human health than we might originally think.
You've probably already heard a lot about gut health and how to heal your gut (for example, here and here). Yet, do you know why? Why is gut health so important? What does our gut microbiome — our gut's population of bacteria — do exactly?
5 Reasons To Heal Your Gut
First, let's lay the groundwork. What does a healthy gut microbiome look like? It should be…
- diverse (think of a rainforest)
- balanced so that there are enough good bacteria to keep potentially pathogenic bacteria in check
- resilient and able to return to a healthy baseline even after stress
- consistent in the above characteristics throughout the entire digestive tract
The formation of a healthy gut begins even before birth. Mothers initially colonize their babies during pregnancy (source), then during passage through the birth canal and breastfeeding (source and source). All of these things affect the development of the gut microbiome. So do antibiotics, diet, and stress (source). In fact, to demonstrate just how dynamic and ever-changing the gut microflora is, consider this…
- transitioning from a low-fat, high-polysaccharide diet to a high-fat, high-sugar diet changed the microbiome within 24 hours (source)
- in animal studies, newborns separated from their mothers for three hours per day within the first two weeks of life experienced so much psychological stress that it significantly changed their microbiomes (source)
Why is it so important that we maintain a healthy gut, or if necessary, begin to heal it?
#1 — A Healthy Gut Strengthens The Immune System
In a healthy gut, inflammation comes and goes. It's a necessary tool that the immune system uses to combat pathogens and promote healing in the body. Pro-inflammatory chemicals take care of the problem, then anti-inflammatory chemicals return everything back to normal.
This is because the gut microbiome and the immune system work together, stimulating and modulating each other. In other words, a balanced immune response requires a balanced microbiome.
For example, a healthy microbiome is necessary for IgA production — an antibody that protects against pathogens. This is one way good bacteria stimulate the immune system.
One way good bacteria modulate the immune system is by fermenting undigestible carbohydrates into short chain fatty acids such as butyrate. Butyrate then increases production of anti-inflammatory immune cells called T regulatory cells. It's important to have enough of these T regulatory cells because they keep the immune system from overreacting.
There are other kinds of T cells, too — such as T helper 1 cells which defend the body against microbial infection, and T helper 2 cells which fight parasites. Notice that these T helper cells initiate the immune response, whereas T regulatory cells resolve it.
Now, here's the kicker: Different bacteria promote production of different T cells.
If the balance of cells is skewed toward the T helper side of the spectrum, autoimmune diseases and allergies can result. This is why it's so important to have balanced gut microflora! None of these T cells are inherently bad — on the contrary, they all provide necessary functions in the body. They must simply be kept in balance, and a balanced gut helps do that.
Immune cells, for their part, have a tolerance for gut microbiota they recognize as normal. They don't attack the good bacteria of the digestive tract! (Source and source.)
#2 — A Healthy Gut Prevents “Leaky Gut”
A permeable intestine, also known as a “leaky gut”, allows undigested macro-molecules, pathogens, antigens, and toxins to pass freely into the bloodstream from the intestine, contributing to the body's toxic load and, of course, inflammation.
Beneficial bacteria in a healthy, balanced microbiome help maintain intestinal wall integrity by…
- preventing pathogen attachment to the intestinal mucosa
- producing short chain fatty acids such as butyrate (and others: acetate, propionate)
Let's take these points one at a time.
Good bacteria prevent pathogen attachment to the intestinal mucosa. Certain molecules called C-type lectins protrude out of the intestinal wall mucosa. They stick to pathogens, and once attached, activate the immune response. However, Lactobacilli bacteria also stick to C-type lectins, effectively protecting the mucosa from pathogen attachment. If Lactobacilli are present in high enough quantities in the gastrointestinal tract, they shield the lectins so pathogens slide off and are excreted.
Why is it better that the body excretes pathogens instead of fighting them with the immune system? An immune response leads to inflammation, and chronic inflammation due to a barrage of pathogenic bacteria leads to a damaged intestinal lining (a leaky gut).
Furthermore, beneficial bacteria indirectly prevent pathogen attachment by preventing pathogen dominance. If there are less pathogens around, there are less opportunities to attach! Beneficial bacteria do this by competing for nutrients and acidifying the gut environment through their byproducts (such as butyrate, see below).
Good bacteria produce short chain fatty acids such as butyrate which help regulate tight junctions of the intestinal wall (source). This means that the gut lining stays, well, tight. No gaps form, and no toxic substances pass into the bloodstream.
#3 — A Healthy Gut Balances Hormones
Scientists have dubbed the gut microbiome a “virtual [endocrine] organ”. In fact, while most other endocrine glands secrete only a small number of hormones, a healthy microbiome can potentially create hundreds of hormones and hormone precursors thanks to its bacterial diversity! These hormones include the short chain fatty acids previously mentioned, neurotransmitters, and more. (Source.)
The gut also helps detoxify hormones from the body. After the ovaries make estrogen, it circulates to organs such as the uterus and breasts, sustaining the monthly female cycle.
Once estrogen makes the full circuit, it goes to the liver, where it is inactivated. It then travels to the gut, where if all is well, it is excreted via stool.
However, in an unhealthy gut, bad bacteria make an enzyme called beta-glucuronidase which re-activates estrogen. Most of the estrogen then returns to circulation, contributing to conditions such as estrogen dominance. (Source.)
A healthy gut also helps rid the body of endocrine disruptors such as BPA and pesticides (source, source, and source).
#4 — A Healthy Gut Promotes Healthy Weight
In addition to increasing nutrient absorption and synthesizing certain vitamins (source and source), gut bacteria affect how individuals hold on to weight. Certain bacteria actually promote obesity. In an imbalanced gut microbiome, these bacteria produce more methane, which slows motility of the digestive tract. This slower transit time increases risk of constipation — and also allows the gut to extract more calories from food. Therein lies at least part of the problem.
The health of the gastrointestinal tract may also regulate insulin sensitivity and determine whether to store food as fat, or use it for energy. (Source and source.)
Additionally, if an individual is already eating poorly, bad bacteria feed off these highly processed, sugary foods and thrive in the inflammatory environment created by them. These bacteria can actually send signals to the brain, demanding more of this junk food!
If we succumb to these cravings, bacterial imbalance is exacerbated even further. In fact, the sugar in processed foods isn't the only culprit. Artificial, sugarless sweeteners such as aspartame act as antibiotics for the gut, killing microflora and creating an environment ripe for proliferation of bad bacteria.
Conversely, remember those short chain fatty acids (SCFAs) that beneficial bacteria produce — butyrate, acetate, and propionate? The gut lining is full of receptors for these SCFAs. Once attached to the receptors, they modulate the “hungry” and “full” hormones, thus regulating healthy appetite and satiety (source).
#5 — A Healthy Gut Protects The Brain
The long-reaching arm of the gut microbiome extends even to the brain, via the gut-brain axis! Among the many hormones a healthy gut produces are neurotransmitters such as serotonin (which promotes happiness) and gamma-aminobutyric acid (which calms) (source).
Furthermore, a healthy gut restores the body's resilience to stress. A hyperactive HPA axis — the endocrine system responsible for the body's stress response — has been implicated in at least some types of depression. This is probably due to the fact that stress causes pro-inflammatory chemicals called cytokines to be released, which travel to the brain and induce neuro-degeneration (source). Women in particular may be more vulnerable to these effects.
Scientists aren't sure exactly how a healthy gut is able to affect the HPA axis and its stress response, but animal studies show that mice born in a germ-free environment have exaggerated responses to even mild stress that can be solved by bacterial colonization (source).
Finally, to further illustrate the gut-brain relationship — many individuals suffering from Irritable Bowel Disease and gut dysbiosis also struggle with anxiety and depression (source).
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