The effect of microbiota on maintaining your health.
Introduction - the benefits of microbiota
The microbiota in our bodies are incredibly beneficial, providing us with a range of health benefits. For example, they help to break down complex carbohydrates and produce essential vitamins such as B12 and K2. They also play an important role in the immune system by producing antimicrobial peptides that protect against infection. Furthermore, they can reduce inflammation throughout the body and even influence neurotransmitter synthesis in the brain via the gut-brain axis.
It’s no exaggeration to say that our microbes are essential to our health. Harnessing these benefits can have an incredible impact on people’s health and wellbeing.
Benefits of a healthy microbiome for babies
Two species of bacteria dominate the microbiota of breastfed babies: Lactobacilli (the friendly bacteria we met in Colonization in the birth canal and Breast-feeding, natural birth, and immunity, part 1), and Bifidobacteria. Bifidobacteria feed on oligosaccharides and produce compounds called short-chain fatty acids (SCFAs) as a waste product.
The three major SCFAs are called butyrate, acetate and propionate. Bifidobacteria also produce a fourth SCFA that’s very beneficial for babies – lactate, or lactic acid. (Yes, this is the same compound that’s found in the mother’s vaginal and breast-milk microbiota). SCFAs “feed the cells of the large intestine and play a crucial role in the development of a baby’s immune system.”
The SCFAs produced by Bifidobacteria perform another essential function: they help us ferment indigestible fibers, such as tough food particles from plant foods, which we’re unable to digest on our own. Without the help of our microbial companions, we wouldn’t be able to fully digest plant foods and extract the essential nutrients they contain.
Training the immune system
Short-chain fatty acids (SCFAs) play a key role in training our immune system as we journey through life. After eating plant foods, large amounts of the three major SCFAs – butyrate, acetate and propionate – are present in the large intestine. According to evolutionary biologist and science writer Alanna Collen, these compounds “are the keys to a thousand locks, and their importance to our health has been underestimated for decades.”
One such lock is GPR43 (G-Protein-coupled Receptor 43). It can be found on immune cells, where it waits patiently for SCFA keys to unlock it. What does GRP43 do, you ask? Some researchers conducted experiments on mice to answer this question. The studies revealed that without these receptors, mice suffer from terrible inflammation and are prone to developing inflamed colons, arthritis or asthma. The same effect occurs if you leave the locks (GPR43) in place but take away the keys (SCFAs).
SCFAs, GPR43s and fat cells
Germ-free mice – mice which are bred without microbiota – are unable to produce SCFAs, because they lack the microbes needed to break down fiber. Their GPR43 locks stay closed and these mice are prone to developing inflammatory diseases.
This points to an interesting fact: GPR43 allows our microbes to talk to our immune system. Our microbes, intriguingly, produce keys in the form of SCFAs so they can tap into the locks on our immune cells, and tell them not to attack.
There is another place where you can find GPR43: on fat cells. Studies on obese people have found they have bigger fat cells than lean people. When a GRP43 lock is unlocked by its matching key, it forces the fat cells to divide instead of growing larger. This causes energy to be stored in a healthy way. Unlocking SCFAs also triggers the release of leptin – the satiety hormone. This explains why eating fiber makes you feel full.
Synthesizing essential vitamins and amino acids
Our gut microbes synthesize vitamins and amino acids that are essential for our health, and which our bodies might otherwise not be able to produce.
Klebsiella, for instance, contains a gene for a protein that makes Vitamin B12. An essential vitamin, B12 balances the nervous system and is critical for brain function. Thanks to the help of Bacteroides, we can borrow genes from our microbes to shape our intestinal walls. The same cells have been found to occur in large numbers in the microbiota of lean humans.
Babies need a lot of folic acid, but they can’t eat foods that contain it. Their microbiotas contain genes that synthesize folic acid from breast milk. Some of us have bacteria that manufacture Vitamin K, which we need for our blood to clot, but which we don’t make ourselves.
This is just another way our tiny companions have co-evolved with us; it would take us a very long time to evolve the genes we need to produce these health-promoting vitamins and acids on our own.
Preventing the overgrowth of harmful bacteria, part 1
Our gut microbiota play an important role in protecting the integrity of the mucosal layer and safeguarding our immune system. Like soldiers holding down the fort, they keep intruders at bay.
However, the reverse is also true: in the presence of illness or infection, dysbiosis can threaten the integrity of the mucosal layer and compromise immunity. When the mucosal layer is damaged, the gut wall becomes porous, and all sorts of toxic compounds, pathogens included, are able to gain a foothold by infiltrating the blood. This is what is known as leaky gut.
Leaky gut causes harm these bad bacteria provoke the immune system, triggering inflammation. It’s this inflammation that’s the culprit behind many of our 21st century illnesses.
So, how do our microbes hold down the fort and keep our borders safe from attack? Butyrate – one of the three major SCFAs – is responsible for patrolling the gut wall and plugging the leaks. Butyrate is a real immune warrior because it seems to be the missing puzzle piece in leaky gut, which is associated with a host of auto-immune diseases.
Preventing the overgrowth of harmful bacteria, part 2
We now know that our gut microbes are like our own personal army; deploying troops to the border to keep enemy forces at bay. One way they do this is by sealing off the porous areas of our gut wall to prevent intruders from slipping into our bloodstream.
Another way that our gut microbes eliminate invading pathogens is by a process called phagocytosis.
Dendritic cells are long-armed immune cells that pluck the good bacteria from the mother’s large intestine and transport them to her breast tissue, to feed her newborn baby. Dendritic cells and other immune cells, which go by the name of macrophages and mast cells, are tasked with the very important function of clearing out pathogens. If you think of your gut microbiome as a garden, it’s the job of these immune cells to pull out the weeds.
Preventing the overgrowth of harmful bacteria, part 3
During phagocytosis, white blood cells that go by the name of phagocytes bind themselves to foreign bodies, including pathogens. After attaching to the pathogen, phagocytes engulf and absorb the intruders; they are skilled defenders against unwanted foreign bodies.
In case you’re wondering what’s behind these names, the prefix ‘phago’ is a Latin word that means to ‘eat’, ‘consume’, or ‘destroy’. Clearly our clever phagocytes do all three. ‘Cytosis’ is the name we use in biology for a process used by cells to intake and expel molecules.