The Interplay Between the Gut and Brain

The classic approach to understanding the gut is that it is simply a collection of organs designed to digest, absorb, and assimilate the food we eat. While this isn’t incorrect, it does not provide the full picture. The gut is full of organisms all working on a wide variety of physiologic actions that help to regulate immune system functioning, detoxification, inflammation, neurotransmitter production and hormone signaling. Without proper maintenance we can have negative effects to our mood, libido, sleep, metabolism, immunity and even our perception of the world and clarity of our thoughts.

Ok, so how do things get out of hand? The overall health of our mind and body is dependent on a diverse population of good organisms in our gut, when populations fall and bad organisms take control we get ill. A loss of diversity in microbial species can be attributed to a culture that favors an unbalanced diet low in plant fibers, the overuse of antibiotics as well as overly sanitizing everything. Understanding this may help to explain why we suffer from rising rates of “western” illnesses that are not seen nearly as much in traditional, mostly agrarian cultures.

Depression, ADHD, obesity, autism, psoriasis, rheumatoid arthritis, cardiovascular disease, Crohn’s disease, asthma and Alzheimer’s have been linked to inflammation in the gut. The causes of gut inflammation vary from person to person but generally stem from poor dietary choices and chronic stress. Consuming a diet high in sugar elevates blood sugar levels which stirs up inflammation in the bloodstream as excess sugar can be toxic if it isn’t swept up and used by the cells. It also triggers a reaction called glycation – the process by which sugar binds to proteins and certain fats, resulting in deformed molecules that function inefficiently. The body recognizes these molecules as abnormal and sets off an inflammatory reaction. In the brain, these structures contribute to degeneration of the brain and its functioning.

The degenerative effects of our dietary choices do not stop at sugar. The ratio of omega-6 to omega-3 fats also come into play. Omega-6 fats dominate the western diet; these pro-inflammatory fats are found in the many vegetable oils used for manufacturing of all processed foods and have been linked to an increased risk for brain disorders. Omega-3 fats, on the other hand – ones found in olive oil, fish, flaxseed and grass-fed animals – boost cognitive function, help to thwart inflammation and can actually counterbalance the detrimental effects of high consumption of omega-6. Anthropological research has revealed that our ancestors consumed a ratio of omega-6 to omega-3 fats at roughly 1:1. Presently, the average western diet is made of as much as 10-20 times more omega-6 fats than what our ancestor ate.

Inflammation due to poor diet elevates a stress hormone called cortisol, which causes some damaging effects on the gut. These elevated levels have the ability to change the mix of bacteria, increase the permeability of the gut lining, and enhance the production of inflammatory chemical coming from immune cells, called cytokines. These cytokines ramp up inflammation in the gut leading to further permeability and also directly and negatively affect the brain making it more susceptible to mood disorders. This effect was studied by Japanese researchers who looked at mice that lacked a microbiome (germ-free mice), it was found that these mice overreacted to stressful situations stemming from an exaggerated HPA (hypothalamus-pituitary-adrenal) response. In other words, the lack of beneficial organisms in the gut can lead to a more damaging outflow of cortisol, thus leading affected individuals to perceive certain events as more stressful than those who have a healthy gut.

Cortisol is also uniquely tied to our circadian rhythm – the ebb and flow of hormones through the 24-hour day that factors into our biology and whether or not we’re feeling alert or tired. Insomnia is a common symptom in mood related disorders and its now known to be linked to the health of our gut. Without optimal health in our gut environment we cannot produce adequate levels of serotonin – an inhibitory neurotransmitter necessary for sleep and mood regulation. Roughly 80% of the amount of serotonin in the body is manufactured by the nerve cells in your gut and many neurologists and psychiatrists are beginning to realize that medications are often less effective in treating sleep and mood disorders than dietary changes are. Interestingly, it is thought that the actual mechanism for modern antidepressants may have nothing to do at all with their effect on serotonin and everything to do with decreasing inflammation.

Another widespread brain disorder linked to the gut is ADHD. The inhibitory neurotransmitter GABA is seen as being largely deficient in the brains of ADHD children. Deficiencies in GABA activity would mean that areas of the brain would be put into overdrive. So what’s triggering this lack of GABA, and how can we increase brains levels? GABA is manufactured in the body from the amino acid glutamine, but the conversion of glutamine requires the presence of what are called cofactors – chemicals necessary for a specific reaction to take place. Specifically, this conversion demands the affected body to be able to absorb and assimilate both zinc and pyroxine (vitamin B6) through food sources, yet without healthy gut flora these cofactors cannot be processed efficiently thus leading to the observed deficiency.

At one point in time it was largely thought that the instance of a “gut feeling” was nothing more than some ambiguous association between the interworking’s of our gut and brain, however upon further investigation it has been shown that there is, in fact, a distinct connection governing this relationship. Serving as a direct link, the vagus nerve that controls impulses and relays information from our gut to our brain and it is for this reason that the health of our gut plays a large role in cognitive function. By understanding that there is a connection, we can find a better way to promote health and prevent diseases.