The Charger Blog
Beatrice Glaviano ’26, a nutrition sciences major, explains the role bacteria can have on the gut and on the entire human body, making the science of these tiny but impactful organisms digestible and applicable to our daily lives.
January 23, 2024
Does anyone remember the show My Strange Addiction? If you don’t, let me provide a refresher: My Strange Addiction was a documentary series featuring unusually compulsive behaviors of individuals, ranging from things like eating non-food items to strange daily habits. Many of these behaviors were the result of psychiatric conditions such as OCD (obsessive-compulsive disorder), PICA, Alzheimer’s – the list goes on.
While I don’t have any of the conditions listed above, I’d totally munch on a traffic light if I wouldn’t get electrified and die a meteor-marshmallow death. Think about it: Would electricity taste spicy or zesty? Would a higher voltage be the equivalent of bumping up the heat level in hot sauce? I feel like this is an important thing to know.
For science, obviously.
Unfortunately, this article isn’t going to be about the bizarre habits of human beings. Today, we’re tapping into one of my new obsessions: bacteria.
Now, I can imagine that a good handful of you saw the word ‘bacteria’ and immediately clicked out of the tab, which is perfectly fine. Bacteria can be nasty, and they’re kinda weird, to be honest. As a very basic biological definition, bacteria are these super-duper-ultra-small organisms that live alongside us and other organisms. These beings are unicellular, meaning that they themselves, as one cell are a living body, and have their nucleus and organelles floating around inside of them.
Think of it as an Amazon department, just minus the organization part. I realize that one typically associates bacteria with being bad, which is a fair assumption to make. Bacteria are responsible for a lot of illness and disease and tend to grow faster than we can kill them – like ants, in a way.
(That being said, the author does not condone ant genocide. Please do not find your local anthill colony and declare war. Ants serve the environment as natural predators of other insects, and also help pollinate the planet.)
Despite being known for their adverse properties, it’s vital to acknowledge that some species of bacteria – particularly the ones living within us – can also be immensely helpful and influential to our well-being. What if I told you that you could potentially fix your lactose intolerance because you decided to eat a lot of Bifidobacteria, a species of bacteria that metabolize the sugar found in milk (lactose) (Goodrich et al.)? What if I told you that some bacteria convert unabsorbed dietary sugars (like lactose) and alcohols into short-chain fatty acids that “promote the growth of intestinal epithelial cells and control their proliferation and differentiation” (Quigley)?
Minds blown yet? No? Well, buckle up, and welcome to a little something I like to call:
The Gut Microbiome: An Informal Literature-Based Analysis of the Beings in Our Bodies
Want to know something freaky? As the human genome consists of roughly 23,000 genes, the gut microbiome encodes more than three million that are responsible for the production of thousands of metabolites (Rinninella et al.) within the human body. In the field of nutritional sciences, there is plenty of information on what foods to eat and how they impact one’s health, yet there tends to be little to no knowledge about the bacteria within the body and what they do for us.
Now, as an emerging topic of interest, the gut microbiome (a collection of complex ecosystems consisting of hundreds of bacterial species within the human gastrointestinal tract) and its impact on human metabolic activity, immunobiology, and homeostasis is being given the spotlight it deserves.
Despite the fact that bacteria are unicellular organisms, it’s common to see them form colonies in which they work together to execute a series of functions that will increase their survival. On that note, the gut microbiome can be described as a collection of complex ecosystems consisting of hundreds of bacterial species that happen to decorate the human gastrointestinal tract. Similar to how they produce a higher genomic yield, “the number of bacteria within the gut is approximately 10 times of that of all the cells in the human body” (Quigley).
Us human beings are constantly creating cells through mitosis (non-sex-specific cells) and meiosis (sex-cell specific) in order to repair and maintain our bodies. Normally, this process takes about 24 hours, but some cells are capable of expediting that process. Bacteria, on the other hand, can replicate in minutes, giving them a clear evolutionary advantage when it comes to populating certain environments.
The human GI tract consists of the mouth, esophagus, stomach, small and large intestine, and other organs. There are plenty of spaces for bacteria to live in, yet the bacteria themselves tend to be particular about where they thrive. Typically, the bacterial inhabitants of our bodies tend to prefer the lower GI tract, mainly consisting of the small and large intestines. In this area, an ecosystem of about 300 to 500 bacterial species can be found (Quigley) with the vast majority of them being anaerobic bacteria (meaning that they do not rely on oxygen to live).
The dominant phyla of the gut microbiome include Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobaceria, and Verrucomicrobia, with Firmicutes being composed of more than 200 different genera, i.e. Lactobacillus, Bacillus, Clostridium, Enterococcus, and Ruminococcus (Rinninella et al.). Essentially, it wouldn’t be incorrect to say that human beings may be more bacteria than we are, well, humans.
But why are these little organisms so vital to our health? Aren’t they the enemy? Well, for starters, there is no true such thing as “good” or “bad” bacteria, and this ideology applies to any living organism. All organism systems – whether plant, animal, bacteria, viral, or even human –work to ensure the survival of that organism through whatever evolutionary means necessary.
To simplify, the bacteria of the gut microbiome happen to benefit us unknowingly by executing their normal biological processes. In fact, they’ll go so far as to defend themselves (and inversely, us, the host) from other bacterial species such as Shigella or Campylobacter, which are capable of penetrating the intestinal mucosa resulting in the production of a bloody, mucoid diarrheal stool mixed with inflammatory substances. Sounds ravishing, doesn’t it?
The gut microbiome serves more functions than merely providing their host protection from malevolent bacteria. More commonly, gut bacteria are known to be key regulators of digestion in the GI tract. In particular, commensal bacteria play a critical role in the “extraction, synthesis, and absorption of many nutrients and metabolites, including bile acids, lipids, amino acids, vitamins, and short-chain fatty acids (SCFAs)” (Rinninella et al.). Many of these molecules, such as amino acids or lipids, serve as building blocks to form larger molecules such as proteins that manage a variety of metabolic functions within the human body.
SCFAs, on the other hand, are a bit more specific. They are created as a product of unabsorbed dietary sugars (i.e. lactose) and alcohols that are then used to “promote the growth of intestinal epithelial cells and control their proliferation and differentiation” (Quigley). It’s quite remarkable – without realizing it – that microbiota are capable of aiding in the recovery and longevity of the epithelial lining of the intestines, which may prove to be vital to the regeneration of intestinal lining for those diagnosed with IBD, IBS, or other diseases.
This lining tends to be made of simple columnar cells that specialize in secretion and absorption, which makes perfect sense as the body must be able to extract the nutritional value from foods (micro and macromolecules) in order to utilize them for energy, bodily repair, synthesis of other substances, and other really cool stuff. So, when it’s damaged, it will be harder for the body to draw in those nutrients in order to utilize them. However – and I’m not hating on bacteria; clearly, they’re very cool and very helpful – I hate to be the one to say it, but how the heck did they get there? Don’t we have an immune system? Isn’t our stomach (which is mostly a bunch of HCl (hydrochloric acid)) supposed to like, y’know, kill these things? Well, let’s talk about that.
Firstly, as it was mentioned before, bacteria are everywhere. They’re on your computer, living in your water bottle, scurrying across the crispy chocolate edge of your Snickers bar as you watch Markiplier’s most recent upload. They’re everywhere. Mind you, these little guys breed quicker than rabbits, and the 99.9% of the bacterial population that your bleach killed will be pretty much overrun by your next snack break. (This isn’t to say bleach isn’t good, but once the bleach is no longer present on a surface, well, sayonara cleanliness.)
Interestingly enough, your skin (a cutaneous membrane) actually excretes an acidic barrier to prevent bacterial and fungal growth because it knows you want to touch everything in plain sight. But, Beatrice, you say to me, that still doesn’t explain how they got into our body! Patience, young padawan. We’re getting there.
Let me ask you this: how are babies made? If you don’t know, it’s when mommy and daddy love each other very much and KABLAM: baby. Short and sweet, amirite? Absolutely not. Not only did your creation involve a bunch of cellular conversation, chromosome pairing, cellular division (meiosis), and whoever had an XX or XY chromosome lying around, but it also included a lot of unknown. Not every birth goes to plan, nor pregnancy. Abortions happen. Miscarriages occur. Plenty of things can go wrong but you did not. You’re here, and if anyone tells you that you do anything otherwise, they can eat a formaldehyde-filled-limp-noodle of a tapeworm.
Anyhow (I’m serious about the tapeworm; they’re nasty), there’s a reason why I’m bringing babies into the conversation. When you are born, you are born completely devoid of any bacterial interaction. The uterus, responsible for keeping a fetus safe during its development, does not want any bacteria to get in and potentially cause harm to the fetus. However, once approximately nine months have passed, the child is ready to enter the world. Pertaining to preterm infants (though I’d surmise this would also apply for on-time infants), following one’s birth, “microbiota colonization is challenged by organ immaturity and environmental factors such as antibiotic use, hospital stay, and enteral feeding” (Rinninella et al.).
Every human being who touches you, the blankets you were swaddled in, and the milk you were given as a newborn shape the core contents of the gut microbiota you will have for your life. The milk – side note – is especially important, as it will contain antibodies that will protect the baby seeing that their adaptive immune system has not been established yet. Any man-made formula will lack those specific mom-made antibodies that are unique to her and her child, even if they’re more fortified with nutrients than Fort Knox.
Eventually, though, humans grow up and by maturity, “one’s specific set of bacteria is “due to the influence of genetics, environment, diet, lifestyle, and gut physiology” (Rinninella et al.). For example: growing up on a farm. One will undoubtedly have a stronger immunity toward animal-borne illnesses, as they have grown up around animals their entire lives. Vice versa, those who have grown up in a city setting may have a stronger defense towards air-borne illnesses or even pollution as a whole.
If you were to swap those populations, it would be likely that both have a higher chance of developing illness. Bringing food into the conversation, I’ve met many people who have grown up on farms and have tried more processed foods, and not only is there a massive difference in taste, but their body seems to reject the idea of anything ‘unnatural,’ so to say.
Obviously, environment plays a crucial role in determining the establishment of the gut microbiota, but variations may also be determined by “enterotypes, body mass index (BMI) level, and external factors such as lifestyle, exercise frequency, ethnicity, and dietary and cultural habits” (Rinninella et al.). Clearly, it’s not just where we start in our lives, but what we do with it.
In nature, symbiotic relationships are a mutually beneficial arrangement that goes both ways. For instance, there is no point for a remora to attach itself to a shark if it doesn’t get a free meal. Inversely, should the remora not free the shark of pests, there is no reason to offer it protection. If a human being doesn’t provide their gut microbiome with the proper nutrients, stable environment, and other factors key to the survival of that species, that specific type of bacteria will dwindle in population.
Case in point, as mentioned before, Bifidobacteria increase in abundance in those who are lactase non-persistent (AKA lactose intolerant) but consume dairy products anyway (Goodrich et al.). This happens as a result of the human body being unable to break down the lactose itself, giving the Bifidobacteria a free meal. So, instead of getting a stomachache, you just get a boost in bacteria. (I’m honestly not sure if that’s comforting, but uh... congrats on the new neighbors, I guess? I’ll see my way out.)
Another interesting determinant of the gut microbiome would also be associated with BMI. I know it’s controversial, but hear me out on this one. BMI – while mostly being garbage-diet-culture nonsense – is simply weight in relation to height. Typically, it’s used as a very basic measurement of one’s health and happens to clue doctors into health problems pertaining to obesity or those who are underweight.
As a nutritional sciences major, I’m not telling anyone that BMI is an accurate or up-to-date system, and it should never be used to determine one’s health in a serious fashion. The world’s best bodybuilder could have a BMI of 30 and be one of the healthiest people on the planet, okay? Okay.
According to several studies, they have demonstrated that “gut microbiota variations are correlated with increased or depleted production of SCFAs that may respectively contribute to the pathophysiology of obesity or AN [Anorexia Nervosa]” (Rinninella et al.). If SCFA levels were to decrease, it would be logical to assume that one’s ability to repair their intestinal lining may be impaired, making it harder to absorb nutrients. As a result, this may lead to an increased appetite, as the body, while getting the calories, isn’t quite getting the nutrients from those calories.
Additionally, it may be proper to note that “obesity is associated with changes in the composition of gut microbiota, including lower species diversity and shifts in the abundance of genes involved in metabolism” (Rinninella et al.). This could be due to an intake of less nutritionally dense food, intolerances, or even pre-existing health conditions. With this, interventions such as pre and probiotics appear to be potential solutions to manage these patient populations. Remaining on the topic of disorders and conditions, IBD and IBS specialists are also looking to the gut microbiome for answers.
Interestingly, Ulcerative Colitis (UC) patients have displayed a “decreased abundance of butyrate-producing bacteria Roseburia Hominis and Faecalibacterium prausnitzii has been observed in UC patients relative to controls” (Rinninella et al.). To quickly recap, UC is an autoimmune disease that causes irritation to the colon by producing ulcers along that area of the digestive tract. These ulcers can be ripped out by food, leading to varying levels of internal bleeding, and the condition itself can lead to several health complications if not taken seriously.
Considering that Roseburia Hominis and Faecalibacterium prausnitzii are bacteria associated with the production of butyrate, a SCFA containing anti-inflammatory properties, it would make sense why this patient population would have a shortage in these species.
At this time, the author encourages all readers to take five. Stretch, drink some water, do some jumping jacks. This is a lot of writing to get through, and brain melt is real.
Did you take the five? Good. Welcome back to bacteria, baby.
So, let’s recap:
Yeah, it’s a lot, I know. Aside from helping us maintain intestinal lining and producing stuff like vitamin K or even SCFAs, how does the presence of bacteria truly impact human health? We can buy vitamin K and SCFAs off the shelf, or even treat UC with immunosuppressants such as Remicade or Humira. Why are all these pasta-shaped microscopic thingies so vital?
For one, new research is showing that the gut microbiome may play a role in the prevention of CNS-related diseases and disorders. Alzheimer’s, for example, is one of the worst degenerative diseases out there. Even though it’s not a direct cause of death, it will certainly lead to it as the cerebral hemispheres of the brain slowly waste away. Considering Alzheimer’s association with age, note that for individuals “over the age of 70, gut microbiota composition can be affected by digestion and nutrient absorption changes and immune activity weakness” (Rinninella et al.).
As a whole, aging involves the slowing down of biological processes. Those at an elderly age typically find it harder to move around, digest food, recover from illness, and are more susceptible to illness and infection as a whole. In terms of bacteria, “a Bifidobacteria decrease may partially explain low systemic inflammatory status and malnutrition in older adults” (Rinninella et al.) Not only do these bacteria prevent infection, but they also produce vitamin B alongside those super swag SCFAs I’ve been mentioning.
But, let me ask you something: How do you think bacteria and man-made medicine, such as antibiotics, get along? If you assumed ‘poorly,’ you would be incredibly correct. The human body is a bit lazy. If it doesn’t need to produce antibodies because it’s getting them from an outside source, it won’t, henceforth why it is extremely important for one to not abuse the medication.
What’s worse, though, is that antibiotics are notorious for messing around with the gut microbiome. In the eyes of antibiotics, bacteria = bacteria, no matter if it’s helping you fight whatever infection you have or not. Keeping this in mind, the “alteration of the microbiome composition depends upon the antibiotic class, dose, period of exposure, pharmacological action, and target bacteria” (Rinninella et al.).
Essentially, even if you’re on a weak class of antibiotics, the period of time in which you’re taking them could have a profound effect on the health of one’s individual gut microbiome. What this is all adding up to is elderly populations may have a poorly developed gut microbiome, which may be potentially keeping the inflammation of their body at bay and ensuring nutritional absorption, because of the pharmaceuticals they’re on. I cannot speak for all medications, but I believe that man-made and nature don’t quite get along.
Getting back into Alzheimer’s, any sort of tissue degeneration is going to leech a ton of inflammatory substances. Within the CNS, the neuroglial cells of that area are responsible for a whole bunch of cool stuff. Astrocytes – star-shaped cells responsible for the blood-brain barrier as well as brain cell nutrition and support – and microglial cells that act as the brain’s cleaning crew are some main players in the CNS field.
Similar to how the other cells in our body lose oomph as we get older, our brain cells do the same. Those microglial cells don’t do as well of a job as they used to, and the brain is more prone to inflammation as a result. In a new study, though, a group of scientists found that a “high-fiber diet changed the types of bacteria in the gut microbiome, increased the production of SCFAs, and reduced the expression of certain genes that control inflammation in the brain” in mice (https://www.facebook.com/NIHAging).
Bacteria, if you haven’t noticed, like ‘crunchy’ things. By this, I mean that they like carbohydrates a lot, so similar to how one may chew on beef jerky because it lasts longer, bacteria do the same with any high-fiber food. Adding the fact that when bacteria like something they multiply. Boom: more bacteria, more functionality, and a higher chance for the host to benefit.
Now, this is all very cool and all, but apparently the scientists had something else up their sleeves. It’s a little freaky, but consider the team “transplanted a young gut microbiome into old mice and an aged one into young mice” (https://www.facebook.com/NIHAging). Yeah: it’s weird, I know. What’s worse is that both groups were made to stroke to test any difference in the mice’s recovery, and it turned out that the older mice with a younger gut microbiome had a 50% increase in stroke survival. That’s insane. That’s actually really, really insane.
Given this discovery, many are intrigued by the possibility that a similar result may occur in diseases such as Alzheimer’s. If we could find a way to use naturally occurring bacteria to encourage the healing and proliferation of the human brain, so many disorders and diseases could be cured, or at the very least, managed more effectively.
If you’re not in awe, then I have no clue what else I could do to possibly impress you. Personally, despite being exhausted as I’ve been writing this paper over the course of an entire week, I’m going to read this in two days and start bouncing off the walls. Also, this brings us to our fourth and final point:
The gut microbiome has a clear influence on human health.
As someone who is basically chasing a degree in nutrition, the best thing I can advise (please don’t quote me on this) is to literally have the most diverse diet you can possibly manage. Eat veggies. Eat cheeseburgers. Try kombucha and other fermented foods. French toast? Sure. Eat the foods that make your body, soul, and heart happy, and your health will pay you in kind.
Those rumors that you can’t eat after 6 p.m. or 8 p.m.? Out the window. You’re hungry, just eat. Boom. Problem solved. Your body is constantly living, dude. Just because you go to sleep doesn’t mean your heart stops beating or that your brain shuts off. The bacteria in you are also living (and dying, just like your own cells) constantly. If they don’t have the fuel to do what they need to do, they won’t do it. Simple as that.
I hope everyone found this article to be educational, and relatively easy to read. I do my best to make sure anyone from any field can understand my work, but sometimes, it can be more than difficult to do so. As we continue the second week of school, remember to stay warm, stay grounded, and enjoy life to the fullest extent possible. You’re here to learn, and sometimes that will be done in ways that you may not necessarily agree with. I encourage all of you to keep learning, and if you don’t know what to learn about, well...
Google is alive and well, haha. Look up a TED talk. Choose a random book to read. I believe in you.
Alrighty everyone, I believe that’s all for today. Sending much love and hugs to you all.
Peace, love, and peanut butter,
Beatrice
Beatrice Glaviano ’26 is a nutrition sciences major at the University of New Haven.
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