Your Gut Microbes Matter More than You Think!

Your body plays host to an incredible 100 trillion microscopic organisms, outnumbering human cells by a ratio of 1.3 to 1. The bulk of these microbes can be found in your gut, where they fulfill various vital functions necessary for your mental, emotional, and physical wellness.

Who is there?

Your gut microbiota is the collection of microorganisms – bacteria, archaea, yeasts, and viruses – in your gut. Weighing a little over 1 kg, your gut microbiota is nearly as heavy as your brain and has approximately 150 times more genes than your genome. The combined genomes of the microbes in your gut make up the gut microbiome.

Just like your fingerprints, the composition of your gut microbiota is unique to you and is reflective of your diet, lifestyle, age, antibiotic consumption, and genes. Bacteria from two major phyla, Firmicutes and Bacteroidetes, largely make up your gut microbiota, alongside smaller population of Actinobacteria, Fusobacteria, Proteobacteria, and Verrucomicrobia. The balance of Firmicutes to Bacteroidetes serves as an essential measure of gut health.

The human gut is first populated by microbes immediately after birth. The initial gut composition is influenced by several factors such as the method of delivery, type of feeding, birth weight, and time spent in the hospital. Generally, the guts of babies born vaginally have high numbers of Lactobacillus species, which are normally present in the birth canal. On the other hand, those delivered through c-section mostly harbour Clostridium (Firmicutes) and other potentially disease-causing microbes (pathogens) like Propionibacterium (Actinobacteria), Staphylococcus (Firmicutes), and Streptococcus (Firmicutes), which can be found on the mother’s skin and in the hospital environment.
Additionally, breastfed babies have more beneficial microbes like Bifidobacterium (Actinobacteria) and Lactobacillus (Firmicutes), and lower numbers of Escherichia coli and Clostridium than formula-fed ones.

Gut colonization has a strong impact on brain development during the first few weeks after birth, as well as subsequent childhood behaviour. It is generally accepted that the ideal infant gut microbiota is that of a full-term vaginally delivered and exclusively breastfed baby with no prior exposure to antibiotics.  

An infant’s gut microbiota evolves, becoming more diverse during and after the first year of life in response to weaning and antibiotic treatment. It becomes more stable by the age of 5, closely resembling that of an adult between the ages of 7 and 12.

What are they doing?

Your gut microbiota contains a larger gene pool than your genome, enabling them to perform a broad variety of functions that your body is not capable of. You and your gut microorganisms have a mutually profitable relationship. You provide them with a home and consistent nourishment through your meals, and they reciprocate by producing numerous essential substances that your body needs to function. The gut microbiota can be likened to a sophisticated power plant, with an assortment of machinery that carry out various important activities.

They help with food digestion

Your gut microbes help convert carbohydrates (both digestible and indigestible) and proteins in the food you consume into small molecules which your body then uses for energy, immune system regulation, growth, and cell repair. Plant starches and fibres are indigestible carbohydrates which the Bacteroidetes and Firmicutes in your gut convert into short-chain fatty acids (SCFAs) – principally acetate, butyrate, and propionate. Short-chain fatty acids provide energy for your intestinal epithelial cells and support your health in numerous ways. Butyrate, for example, eliminates colon cancer cells and fortifies the gut mucus barrier which keeps microbes from invading and damaging tissues. Propionate prevents cancer, reduces blood cholesterol levels, and guards against weight gain, while acetate assists with proper heart and kidney function.
Firmicutes in your gut help your body extract energy from food and store this energy as fats.

The intestinal epithelium – a tissue that covers the inner surface of your gut – is made up of a single layer of cells known as the intestinal epithelial cells. These cells produce a viscous, gel-like substance that forms the mucus layer or gut mucus barrier, which helps absorb digested nutrients and protects your body from infection.

They produce essential vitamins

Your gut microbiota manufactures vitamin K and most of the water-soluble B-group vitamins which your body needs to function properly. Vitamin K promotes strong bones and facilitates blood clotting and wound healing. Meanwhile, the B-group vitamins help release energy from food and are important for proper cell functioning. The bulk of these vitamins is produced by species of Bifidobacterium and Lactobacillus.

They help break down ingested xenobiotics

Chemical substances that are foreign to your body are called xenobiotics. These include synthetic food dyes and additives, drugs, micro- and nano-plastics, pesticide residues in food and drinking water, and other environmental pollutants. Xenobiotics may accumulate in your body and increase your risk for cancer and autoimmune disorders like multiple sclerosis if they are not properly broken down and excreted. Fortunately, the microorganisms in your gut can modify the chemical structures of ingested xenobiotics, transforming them into less toxic forms that can be easily excreted.

Plant-based foods, such as fruits, vegetables, herbs, spices, tea, and chocolate, contain compounds called polyphenols, which are powerful antioxidants. However, only 5% of these polyphenols are absorbed in your small intestine because they are identified as foreign compounds by your body. Thankfully, two beneficial gut bacteria, Lactobacillus and Bifidobacterium, specialize in transforming 95% of consumed polyphenols (e.g., flavonoids and phenolic acids) into active and easily absorbed compounds.

Antioxidants are molecules that prevent, or limit cell damage caused by unstable molecules called free radicals. Cell damage may increase the risks of diabetes, cancer, autoimmune disorders, inflammatory and cardiovascular diseases.

They prevent infection and improve immunity

Microorganisms constantly compete with one another for nutrients, space, and other limited resources in their immediate environment. Many bacteria secrete antimicrobial substances called bacteriocins that kill or harm their bacterial competitors. For instance, species of Lactobacillus in your gut produce lactic acid that destroys the cell membranes of bacterial pathogens.

The mucus layer serves as a physical barrier that stops your gut microbes from infiltrating underlying tissues but permits certain molecules such as digested nutrients to pass through to your bloodstream. It also provides nourishment and attachment sites for gut microbes. Pathogens can use these attachment sites to gain access to your tissues, leading to infection. By consuming limited resources (nutrients and attachment sites), your gut microbiota, (e.g., Lactobacillus and Bifidobacterium) can prevent these invading microbes from colonizing the gut mucus barrier.

Contained within the cell wall of certain pathogens are endotoxins which are only released into the surrounding environment upon their death. Endotoxins may cause chronic inflammation, non-alcoholic fatty liver disease or septic shock if they can cross the gut mucus barrier and enough gets into your bloodstream. Fortunately, Bacteroidetes can help fortify the mucus barrier and also reduce endotoxin levels in your gut.

Your gut is a giant immune organ that houses approximately 80% of your immune cells, and it is the hub for the two-way communication between your gut microbiota and immune cells. Known as the gut-immune connection, this dialogue is moderated by intestinal epithelial cells, and regulates how your body defends itself against infection.

They communicate with your brain

Your gut microbiota interacts regularly with your brain along a communication network known as the gut-brain axis. This bidirectional exchange allows your gut microbiota to influence some brain functions, while the brain also governs activities (e.g., digestion and immune response) taking place in your gut. Thus, the mere thought of your favourite food can stimulate your stomach to release digestive juices. Similarly, a sense of dread can lead to diarrhea, indigestion, or loss of appetite.
This dialogue takes place via different pathways along the gut-brain axis, with the quickest being the vagus nerve.

The vagus nerve is the body’s information superhighway that facilitates a two-way dialogue between your brain and other areas of your body. It originates from the brain and runs down your neck, midsection, and gut. As it travels, it forms multiple branches to numerous organs, delivering instructions and collecting feedback.

The human gut is often dubbed the second brain due to its network of 500 million neurons (nerve cells) collectively called the enteric nervous system (ENS). The ENS can operate independently of the brain coordinating the various processes in your digestive tract, but it is not capable of thought. However, it is connected to your brain via nerves, the largest being the vagus nerve. Your gut sends information to your brain through the vagus nerve using neurochemicals produced by your gut microbiota.

Neurochemicals – your body’s chemical messengers – allow neurons to converse with each other and other cells in your body. They control virtually all bodily functions including breathing, muscle movement, heart rate, mood, stress, hunger, and sleep.

Gut microbes are known to secrete a range of neurochemicals that include glutamate, serotonin, norepinephrine, dopamine, SCFAs, Gamma-aminobutyric acid (GABA), and bile acids. The “happy hormone” serotonin, for example, influences mood and sleep-wake patterns, reduces food cravings, and even helps with wound healing. However, too much serotonin in the gut can induce nausea and vomiting. Dopamine, the “pleasure chemical”, assists with memory, boosts motivation, and stimulates pleasure, whereas GABA manages the body’s reactions to stress, fear, and anxiety. Glutamate helps with memory and learning, while bile acids promote fat digestion and help remove cholesterol from the body.

Your gut microorganisms produce around 90% of your body’s serotonin and half of its dopamine. Low levels of serotonin can cause insomnia and mental disorders like depression and mania, whereas insufficient dopamine levels have been associated with Parkinson’s disease and addiction.

Troubled “gut feelings”? What does it mean?

The key to a healthy gut is maintaining the right balance between beneficial and pathogenic bacteria. However, stress, incorrect diet, drug and alcohol consumption, and antibiotic treatment can disrupt the delicate balance of the trillions of bacteria that live in your gut. This imbalance is referred to as gut microbiota dysbiosis, and often has adverse effects on your overall health. It can impair immune system function, impede nutrient absorption, and interfere with blood sugar regulation. Furthermore, brain function can be impacted leading to mood, memory, and behavioural changes.

Gut microbiota dysbiosis has been linked to many illnesses varying from mild stomach cramps and diarrhea to heart diseases, allergies, obesity, colorectal cancer, and type-2 diabetes.
Hippocrates (460 BC) – the renowned Greek physician-philosopher – recognized the significance of gut microbes in well-being and illness over 2000 years ago by famously proclaiming, “All disease begins in the gut”.

Eubiosis or normobiosis describes a healthy and balanced gut microbial ecosystem, while the disruption of such a system is known as dysbiosis.

Stress, for instance, drives your body to release certain hormones that modify the composition of your gut microbiota. Research has linked psychological stress to a reduced presence of beneficial bacteria like Lactobacillus, and an increase in the population of potentially harmful bacteria like Escherichia coli and Pseudomonas, which may also produce enterotoxins. Stress hormones and enterotoxins can damage the protective mucus layer in your gut, and thus reduce the absorption of essential nutrients. This may lead to irritable bowel syndrome (IBS) or chronic conditions such as Crohn’s disease and ulcerative colitis.

Enterotoxins are toxic substances that attack the intestinal tract. They are produced by many microorganisms including Clostridium difficile, and certain strains of Staphylococcus aureus and Escherichia coli.

Additionally, antibiotic intake may increase your risk of developing IBS, a condition characterized by stomach cramps, gas, bloating, diarrhea and/or constipation. Research has demonstrated that those affected by IBS have more Firmicutes in their gut and decreased population of Bacteroidetes and Bifidobacterium.

Scientists have linked gut microbiota dysbiosis to several neurological conditions including Alzheimer’s, Parkinson’s, schizophrenia, chronic depression, autism, and bipolar disorder. New studies suggest that an imbalance of the gut microbiota can influence brain functions through the gut-brain axis.
Studies of depressed patients have revealed deficiencies in SCFAs-producing bacteria like Coprococcus and Dialister, as well as Bacteroides and vitamin B-producing bacteria such as Lactobacillus, Bifidobacterium, and Ruminococcus. Additionally, depressed individuals have been reported to have elevated numbers of Alistipes species, which are known to interfere with serotonin production in the body.

How can you help?

A healthier lifestyle can help restore and maintain a healthy balance of microorganisms in your gut.

Change your diet

Your gut microbiota is shaped by what you consume, and as the saying goes “Garbage in, garbage out”, an unhealthy diet has drastic implications for your overall health.
Eating lots of fruits, vegetables, and whole grains boosts the population of Bacteroides and Clostridium which generate vital molecules like SCFAs and bile acids, while Firmicutes and Proteobacteria numbers decrease. This diet has been seen to benefit the brain and improve mental health, as well as reduce the risk of obesity, type-2 diabetes, cancer, and heart disease. On the other hand, a Western diet full of saturated fats and refined sugar and lacking in fibre encourages Proteobacteria and fat-storing Firmicutes, while diminishing the numbers of beneficial Bacteroidetes and Bifidobacterium. This ultimately causes obesity and an increased likelihood of hypertension, non-alcoholic fatty liver disease, type-2 diabetes, and cancer.
Incredibly, it takes only a day to significantly modify your gut microbiota, so healthy eating can potentially have far-reaching positive impacts on your health.

Add probiotic foods to your diet

Ingesting adequate amounts of probiotics – beneficial live bacteria and yeasts – may help restore a healthy balance to your gut microbiota and provide a multitude of health advantages. Numerous fermented products like sauerkraut, buttermilk, miso, kefir, tempeh, yoghurt, pickles, palm wine, and cheese are rich sources of probiotics, mostly Lactobacillus and Bifidobacterium, and the yeast, Saccharomyces cerevisiae. In addition, probiotics can be purchased as health supplements in capsules, tablets, powder, or liquid forms. Probiotics can inhibit the growth of harmful microorganisms, reinforce the gut mucus barrier, and support the functioning of your immune system. There is also evidence that they may be effective in combating antibiotic-induced diarrhea and inflammatory bowel disease.

Eat fibre-rich plant-based foods regularly

Prebiotics – plant fibres that your body is unable to digest – promote the growth of helpful gut bacteria like Lactobacillus and Bifidobacterium.

Prebiotics serve as food for probiotic bacteria in your gut!

When consumed, prebiotics are broken down by your helpful gut microbes into short-chain fatty acids (SCFAs) which deliver various health benefits. Sources of prebiotics include fruits, vegetables, seaweed, and whole grains. Eating these foods can alleviate stress, depression, and anxiety, fortify the immune system, improve digestion, relieve constipation, and lower blood cholesterol.

Synbiotics are even better

Synbiotics provide a blend of beneficial live microorganisms (probiotics), along with food source (prebiotics) that keeps them viable in your gut.
Research suggests that synbiotics may lower blood pressure and cholesterol, bolster your immune system, promote weight loss, and improve memory and symptoms of mental illnesses. They may also help prevent and treat diarrhea, ulcerative colitis, and irritable bowel syndrome (IBS). You can take synbiotics as dietary supplements or incorporate both high-fibre and fermented foods in your meals.

What other treatment options are available?

Faecal microbiota transplant

Faecal microbiota transplant or simply poop transplant is an unconventional yet promising approach to treating illnesses linked to gut dysbiosis. The procedure entails transferring faecal matter from a healthy donor into the large intestine of a sick individual, to restore a balanced gut microbiota in the patient. Faecal microbiota transplant has proven effective in treating recurring Clostridium difficile infection, a potentially fatal infection of the large intestine (colon) that may lead to chronic diarrhea. C. difficile infection often occurs after a hospital stay or antibiotic treatment.

Psychobiotics

Psychobiotics, a fairly new concept, refers to prebiotics, probiotics, or synbiotics with proven mental health benefits due to their influence on the gut-brain axis. Psychobiotics help strengthen the gut mucus barrier and can enhance the production of mood-altering neurochemicals in your gut. Although the field of psychobiotics is relatively new, studies have already shown that Lactobacillus supplementation can alleviate anxiety, stress, and depression, and even improve the cognitive abilities of those suffering from mild Alzheimer’s and Parkinson’s diseases. However, more research is necessary to figure out which microbes possess psychobiotic qualities, and what implications their prolonged use may have on the gut-brain axis and one’s mental health.

Concluding remarks

We now know that our gut microbiota affects our overall health by combating pathogens and regulating digestive processes, immune system, and cognitive function. Eating the right foods helps restore and maintain a healthy balance of microbes in the gut, thereby lowering our risk of developing health problems. Nevertheless, nutritional needs differ for each person and no single diet is guaranteed to work for everyone.

Advances in ‘multi-omics’ technologies (metabolomics, metagenomics, and nutrigenomics) coupled with machine learning tools have presented new solutions for managing diseases via personalized or precision nutrition. This new field of science relies on genetic data and information from a person’s lifestyle, and gut microbiome, to create tailor-made dietary plans designed to improve health and treat or manage diseases.
It appears that the wise words of Hippocrates (460 BC) – “Let food be thy medicine and medicine be thy food” – are still incredibly relevant today.

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