Delia McCabe has compiled this highly informative breakdown about how your gut interacts with your brain. It also highlights how the probiotic revolution is severely lacking – both in the science and actions. After all, with around 100 trillion bacteria in our gut, how can a few strains rebalance what is out of whack? This is where your qualified naturopath can help.
There is much discussion about gut and brain health today, with many books, articles and ‘influencers’ weighing in on the intimate relationship between these organs.
A deep dive into this topic is not on everyone’s agenda, and truth be told, it is a complex subject.
There’s also a lot we don’t yet know and will likely remain in the dark about for a long while.
Let’s simplify the topic so we can action what we know, without needing to know it all.
And if you really don’t want to know even a little of the detail, and just want to action what evidence-based research suggests, skip ahead to the ‘So, what to do?’ section.
Or, if you’re thinking TL;DR, have a look at the chart further on in the article which summarises the cascade of damage that compromises our brain when our gut health is below par.
A few fun facts before we dive into details:
- We have 100 trillion bacteria in our gut (which is more than the 60 trillion cells we possess).
- We are shy of 21,000 genes, but the microbes in our body contain 4.4 million genes.
- There are (or should be) about 4,000 different species of bacteria in our gut.
- The bacteria in our gut weigh anywhere from 1 – 2.3 kg’s (3 – 5lbs) which is greater than or similar to the weight of the brain at 1.3 – 1.4kg (2.9 – 3.1lbs).
- Over our lifetime we will play host to bacteria that are the equivalent weight of 5 African elephants (between 14,000 and 30,000kg).
- The immune system in the gut is called GALT (Gut Associated Lymphatic Tissue) and represents 70- 80% of our body’s total immune system because this is where the greatest threat to our health (maybe even survival) comes from.
- The surface area of your small intestine is larger than a tennis court, and the active cells that line it are replaced every four days.
- Your small intestine absorbs different nutrients at different places on its vast surface area, with each place requiring different conditions to optimise this absorption.
- The brain and gut have a bidirectional relationship. Think of butterflies in your stomach when your brain perceives a threat, or even excitement.
Detail oriented? This is for you …
> Lipopolysaccharides (LPS) are a substance that is present, and therefore a marker, for a leaky gut – and you can get blood test to check for its presence.
> LPS also lowers the production of brain derived neurotrophic factor (BDNF) and is linked to depression.
> LPS makes the gut more permeable AND can cross the blood brain barrier (BBB) to allow pro-inflammatory cytokines passage into the brain, the presence of which is linked to dementia.
> High levels of baceriodetes (back-ter-oi-de-tees) are a reflection of an unhealthy gut and prevent akkermansia from doing their job properly which leads to LPS and inflammation in fat tissue which leads to unhealthy weight gain.
> Akkermansia bacteria sends a chemical signal which dials up human genes to make more gut lining mucus which increases its home base AND prevents LPS from crossing into the blood stream; the less we have the higher our BMI (body mass index).
> Firmicutes (Fur-ma-cutes) bacteria are a reflection of a healthy gut – they extract calories very efficiently, but if we have too many of them we gain weight.
This means that specific gut bacteria can encourage you to want specific foods, so you help sustain their existence. This is rather sobering!
Gut bacteria influences brain function in a few, interacting ways
How food is digested and therefore how available it is for absorption and utilisation, impacts how effectively vitamins and neurotransmitters are synthesised, for use in our body and brain. For example, 80%+ of serotonin (peripheral) is synthesised in the gut.
How permeable the gut/blood stream interface is, impacts gut health overall, which includes digestion, absorption, inflammation, immunity, and central nervous system (CNS) activity.
Communication between the gut and the brain is controlled by the immune system, the endocrine (hormone) system and the CNS, all of which are under the influence of gut bacteria, and all these systems interact and impact brain health and function.
Our Wonderful Vagus nerve (VN)
The vagus nerve (VN), is called thus from the Latin term ‘vagus’ meaning wandering.
The VN is the longest of 12 cranial nerves and is the primary channel of information between the 100s of millions of nerve cells in the enteric nervous system (ENS), the nervous system that resides in the digestive tract, and the CNS.
The VN is also involved with controlling heart rate and digestion and plays a major role in managing the inflammatory response system in the body.
However, 80% of VN fibres carry information from the organs in the body to the brain – not the opposite way.
- Which is why digestive distress impacts how we feel mentally.
- And, how we feel mentally impacts our gut.
In addition, an increasingly robust body of research is revealing that when the brain becomes inflamed it becomes susceptible to mental health challenges, including anxiety and depression.
Unfortunately, an inflamed brain is also more susceptible to cognitive decline, via the mechanisms highlighted in the chart above.
Gut health and healthy weight
Differences in gut bacteria composition is noted in lean vs heavier animals AND people, which leads researchers to suggest that gut bacteria composition and ratio is directly linked to weight gain or loss.
The ratio of a variety of gut bacteria, including that of those that are excellent at extracting every last calorie from our food, and those that are less so, can become unbalanced.
When this happens, either unexplained weight gain or loss can result.
Unfortunately, for many people, the ratio seems to favour those bacteria that are excellent at extracting calories vs ignoring them, leading to weight gain.
Why? Ultra Processed Foods (UPFs) encourage the proliferation of gut bacteria that are very good at extracting calories, and discourage the proliferation of those that are good at ignoring some of them.
Improving gut health will naturally improve the ratio of the bacteria favouring less scrupulous extraction, which will lead to positive results.
Three main forces working against a healthy gut
Research suggests we can improve our digestive health via improving gut bacteria in as little as 4 days.
Pay attention to the following aspects that undermine gut health:
- Lack of gut-supportive nutrients.
- Exposure to substances that change the bacteria ratio (colonies) eg. Anti-biotics, gluten, sugar, factory foods which include additives, flavorings and preservatives, over the counter (OTC) medication, chlorine, pesticides, fungicides, rodent-cides.
- Stress – psychological, and oxidative stress, which is generated via the above two challenges, and age.
1. As you get older your stomach produces less stomach acid
Stomach acid is also an important requirement for optimal digestion, as it’s required for protein digestion, and also mineral absorption, as well as being an important defense against infections because it sterilizes the food that you eat.
Therefore, a lack of stomach acid will mean indigestion from protein foods, as well as a potential for developing food allergies, as undigested protein molecules may cause difficulties in the small intestine by crossing into the bloodstream and causing allergic reactions.
- The production of stomach acid, also known as hydrochloric acid, declines with age, and a zinc deficiency is also responsible for a lack of this important compound because it’s required to produce stomach acid.
- Bad breath, indigestion indicated by bloating, gas, constipation, diarrhea, and abdominal pain, are all indications of low stomach acid.
Unfortunately, stress also inhibits stomach acid production, as your body is more interested in survival than digestion.
Supplementing with a digestive enzyme containing hydrochloric acid as well as zinc can help your body produce more stomach acid.
What if you are producing too much stomach acid?
The other side of the coin is the production of too much stomach acid, and this can occur due to gut inflammation, which happens when alcohol, tea, and coffee, as well as chilies are consumed in excess.
This doesn’t only cause pain, it also suppresses the production of healthy, protective mucous stomach lining, which further increases sensitivity to any aggravating substances.
- B vitamins, minerals and fats are absorbed when the stomach acid environment is just right, and B12 is absorbed when there’s enough intrinsic factor, which is also dependent on enough stomach acid. Various bacteria and fiber are also required to increase and maximise absorption.
Tiny compounds with an important task
Digestive enzymes form a very important part of the digestive process, as they help to break down the nutrients into smaller components. A major factor that determines how well enzymes can do their jobs is pH, or acidity within the body.
For example, when eating carbohydrates, the digestive enzyme ptyalin is released in your mouth, via saliva, to break down the carbohydrates. The more you chew the better the process of digestion can begin.
- These digestive enzymes are released at different stages along the digestive process, so if you don’t have enough of them, your food will not be broken down into the smaller components that contain the nutrients you need.
Although carbohydrate digestion starts in your mouth, proteins get digested in your stomach, using hydrochloric acid and an enzyme called pepsinogen.
When combined, they produce a powerful enzyme called pepsin, which is capable of breaking protein down into smaller components, and eventually into amino acids, through enzymes called proteases.
- Your body contains over 3000 different types of enzymes, that are continuously working to repair, protect and nourish you, through their biological actions.
- As you get older, the enzymes produced naturally by your body decrease both in number and effectiveness.
By eating more fresh produce, and ensuring that most of it is eaten raw or very lightly steamed, and eating fresh seed sprouts, you can ensure that these precious enzymes are not destroyed, and that you get maximum benefit from them.
- Indigestion occurs when you don’t have enough of these special enzymes to break down carbohydrates, as well as proteins and fats.
The result is that partially digested food ends up in the small intestine, providing food for the bacteria that live there, producing gas, bloating, and digestive pain.
If you don’t have enough enzymes, instead of feeling satisfied and energized after a meal, you will feel listless and tired.
Unfortunately, if you’re not digesting your food properly, your body cells cannot make the enzymes required for digestion, because they aren’t getting the nutrients required to make them, so it’s a vicious cycle.
Keep in mind that … Fats and oils are digested differently 
Fats and oils have to be digested in a completely different way because they are not water-soluble as carbohydrates and proteins are.
As fat repels water, the same water-soluble enzymes can’t digest it.
Your liver produces bile, which is stored in the gall bladder, and which breaks the large fat pieces down into smaller pieces of fat so that the enzyme lipase has an easier time in digesting the fat.
If it’s not doing its job properly, you will end up feeling tired and also experience nausea after eating foods that contain fats and oils.
2. Substances that impact gut health negatively
There ar
e certain substances in food that can inhibit absorption or even compete with each other for absorption, and in so doing reduce the nutrient content of those foods.
These compounds will interfere with absorption and therefore reduce nutrient availability:
- Methylxanthines in coffee, tea and cocoa
- Phytates in wheat
- Oxalates in spinach and rhubarb
- Digestive tract irritants, such as alcohol, antibiotics, painkillers, chilies and caffeine
If you suspect that you are not absorbing nutrients optimally from your food, you can request a stool analysis from your healthcare provider, which will highlight what your body isn’t absorbing.
An intestinal permeability test is also a good indicator of what isn’t being absorbed, as it will indicate the size of the food molecules that are passing through your digestive wall.
Antibiotics impact the diversity and composition of our gut bacteria which can obliterate some and allow others to flourish.
Pesticides and chlorine are bactericidal and therefore toxic to gut bacteria and glyphosate inhibits the synthesis of enzymes produced by gut bacteria, which detoxify foreign chemical compounds.
Elimination … the taboo subject
The large intestine, or colon, primarily prepares the waste material – what’s left over after absorption – for elimination from the body.
Although there is some absorption of nutrients in this area, its main function is to pass waste along to the bowel, then to the rectum, using peristalsis, a consistent series of wave-like muscular contractions.
Cholesterol, dead blood cells, as well as old hormones, are also eliminated from the body in this way.
*In the online ‘Gut and Brain Reboot,’ I give you a simple test to perform at home that will tell you what you to do if you have an ‘elimination’ challenge.
3. Stress
When our lives trigger our brain into believing our survival is at stake, whether that’s accurate or not, it triggers the release of specific hormones that tell the body to be prepared to run, hide or fight.
- To a lesser or greater extent, adrenalin, and then cortisol, is released, which leads to the release of glucose with which to address the stressor. The body goes on the defense which also triggers an immune response.
This is why stress makes us feel ill – we can feel nauseous and our bowels can be impacted.
In addition, chronic cortisol release causes the tight junctions between intestinal cells to become compromised so they can’t do their job effectively anymore.
This allows the pathogenic substances it was designed to prevent from entering the blood stream, to enter.
- Furthermore, stress impacts sleep because cortisol is intimately linked to circadian rhythm and gut bacteria. And sleep challenges impact gut bacteria in ways not yet fully understood.
- Research that examined the gut bacteria of jet-lagged passengers found a correlation between compromised gut bacteria and sleep deprivation.
So, what to do?
As per the three sections above, increasing the intake of nutrient-dense and fibre-filled food, avoiding toxic compounds that impact gut bacteria and reducing stress are the three simplest and best steps to take to improve gut heath.
Step 1
Choose gut supporting nutrients
The bacteria in our gut love fibre, so this is what we need to eat more of. When we eat food that is full of fibre, we naturally crowd out the processed foods that prohibit the growth and proliferation of the bacteria that support optimal gut health.
Many people use probiotics in capsule form. However it is more sustainable to supply the food for good bacteria to proliferate and change ones diet to support such.
In addition, no probiotic can supply the full spectrum of bacteria we requite for optimal gut health.
So, use probiotics as a starting point for improved gut health, but keep in mind they are unable to provide the full spectrum of good bacteria.
- A more natural way to provide the good bacteria with what they need is to eat fermented foods such as kimchi, sauerkraut and miso, which are rich in probiotics.
- Eating prebiotic foods goes a step further by providing food for our good bacteria, and support their growth sustainably:
These are some of my favorite common foods that provide robust prebiotic benefits:
- Artichokes
- Raspberries
- Chickpeas
- Asparagus
- Garlic, leeks and onions
- Red kidney beans
- Savoy cabbage
- Kimchi, sauerkraut and miso
In the process by which the good bacteria metabolize their sources of fuel from our fibre-filled diet they also liberate specific nutrients such as vitamin A, C and K and some B vitamins.
These nutrients are also used to support both mental and physical health.
Unfortunately, age can impact gut health too, and how we digest and absorb the nutrients we consume.
Focus on adding delicious fibre filled foods to your diet vs removing processed ones. You won’t feel deprived and the processed foods will naturally become less appealing.
And unprocessed foods force one to chew more, which supports improved digestion, and they fill one up more than processed foods do, so weight loss is a happy by-product of following this step.
Two different kinds of fibre from the plant kingdom:
Fibre is that part of a plant that is indigestible, which means that your body can’t break it down completely.
# Soluble fibre is capable of being a prebiotic, providing nutrients for probiotics, the friendly bacteria that we need. It also absorbs water, helping to keep waste material moving through the digestive tract, collecting toxins and wastes as it moves along. Soluble fibre also helps to lower cholesterol.
Legumes, psyllium seed husks, root vegetables, oats, rye, broccoli, artichokes, as well as prunes, berries, bananas, pears and apples, are all good sources of soluble fibre.
Insoluble fibre also absorbs water, and helps to soften and bulk the stool up, making elimination easier.
By doing this it also slows down the release of glucose and other sugars, helping to control appetite, and therefore weight gain, as well as decreasing transit time, thus avoiding re-absorption of old hormones and cholesterol which can occur if the stool isn’t eliminated as soon as it’s ready to leave the body.
It can also act like a broom, sweeping up toxins that are in the colon, removing them from the body, avoiding the harm that they can cause.
# Insoluble fibre is found in celery, avocados, flax and other seeds, as well as nuts, whole grains, potato skin, as well as cauliflower, and green beans.
Don’t add wheat bran to your diet, due to the phytates it contains, which may inhibit nutrient absorption.
Rather, obtain your fibre from legumes, vegetables, either raw or very lightly cooked, fruits and seeds, as well as non-gluten grains.
Cooking destroys some fibre and enzymes, so enjoy your veggies as crunchy as possible, remembering to chew them well.
And, processed foods contain vast quantities of sugar, which interfere with absorption, and many additives, which have further negative effects on gut health.
Step 2
Purchase organic or pesticide free fresh produce as much as possible and work on ways to reduce the use of over the counter (OTC) medication.
Activities also damage absorption and include eating on the run. If you eat on the run, not paying attention to each mouthful, you will end up with a pain in your stomach. If you do this regularly, you cheat yourself of the nutrients that are in the food.
# Pay attention to what you are eating AND how you are eating it, taking care to chew each mouthful until the food turns into a ‘liquidy’ pulp.
Also make sure you are properly awake, as being half asleep will impact your digestion in a negative way too.
And eating while watching the news or scrolling on your phone will negatively impact the release of digestion-friendly enzymes, so eat without tech-intervention.
# If you manage your life by squeezing food into the tiny spaces that are left over after accomplishing all your other goals, your digestive system will eventually rebel, and ill health will be the logical outcome.
Step 3
Action ways to lessen your stress burden ASAP, which will increase the quality of your sleep directly, and also the health of your gut indirectly via a reduction in stress hormone production.
And, what should be intuitive, only eat when you are calm.
In conclusion, the intricate and intimate link between the gut and the brain is fascinating and there’s still a vast amount we don’t know about this relationship.
However, we do know that it doesn’t take very long for the gut to respond to these strategies. And the benefits are plentiful and long-reaching and impact your brain directly!
NOTE: No part of this article was generated using AI.
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