The gut is now being called the second brain due to its effect on everything from our mood to immunity.

As it turns out, the gut does a lot more than just digest food, it also produces large amounts of hormones, is a key player in our immune system with 70-80% of all immune cells found in the gut, it houses trillions of microorganisms with at least 1000 different species of bacteria, and has a communication network with the brain known as the gut-brain axis.

Brain and the Gut

The gut and the brain are very closely linked and the bi-directional biochemical signaling system in which the two organs communicate is referred to as the “gut-brain-axis.” The main ways the gut and brain communicate is through the vagus nerve, hormone signals, the immune system, and the bacterial community in the gut.

It is well known that the brain and our emotions have a big impact on our belly. We all have felt that queasy feeling when we were nervous or butterflies when we are excited. What is interesting is just as anxiety in the mind can cause us to have a nervous belly, an unhealthy belly can also lead to an anxious mind. Poor gut health is linked to psychological conditions such as depression and anxiety, and even neurodegenerative conditions such as Alzheimer’s and Parkinson’s.

The gut talks to the brain about hunger levels, digestion/ingestion, the immune system, secretions, visceral sensations, bowel movement control, and the presence of disease or disease-causing microbes.

Homeostasis in the gut-brain axis is critical to gastrointestinal tract physiology and for a balanced emotional state. Disruptions in gut-brain communication are now considered one of the main underlying mechanisms for many physiological and psychological conditions.

Hormones and the Gut

Hormones have an impact on everything from our mood and metabolism to the overall health and homeostasis of our body.

Gut-specific hormones are hormones that are produced in the stomach and small intestine and impact the gut. These include hormones such as ghrelin, which is the hunger hormone and gastric inhibitory peptide, which is associated with digestion.

The gut also produces non-gut specific hormones, as in hormones that are also produced in, and have effects on, other parts of the body as well. One hormone called serotonin, which is known as the “happy hormone” as it is shown to increase mood, is 90% produced in the gut, with only about 10% of its production occurring in the brain.

So as you can probably guess, an unhealthy gut can lead to hormones imbalances and many other symptoms.

Stress and the Gut

Stress has a negative impact on our overall health and the gut is no exception. An independent study has proven that even two hours of stress can change the composition of the gut microbiota.

Unfortunately, stress and gut disorders go hand and hand. Not only are those who suffer from gastrointestinal disorders more likely to experience stress and anxiety issues, but those who experience stress are more prone to developing a GI disorder.

Microbial imbalances can also be presented as and trigger stress. High levels of lactobacillus, for example, are associated with mood swings in patients with chronic fatigue syndrome.

Bacteria in the Gut

I’m sure by now we have all heard about the importance of good bacteria in the gut, but why? Well, it turns out the types of bacteria in your gut and whether you have more good bacteria than bad can have an impact on both your health and your risk for conditions like obesity, diabetes, osteoporosis, autoimmune diseases, depression, Alzheimer’s, etc.

The bacteria in your gut has also been found to impact on your weight. One study found that those who were more prone to be leaner had more Bacteroidetes bacteria than those who tended to be overweight.

It also appears that the types of bacteria in your gut can help prevent infections. A study on Cholera transmission found that certain strains of bacteria in the gut reduce the risk of developing Cholera.

While this may seem far fetched, it really shouldn’t be surprising that these microbes have such an impact on our health as we have so many of them. The human body is about 50% bacteria cells and 50% human cells. Some scientists used to say that we were 90% bacteria and 10% human, but have since taken that back and now say we are about a 50-50 split.

In addition, not all guts are alike, the human-microbe project found variability not only in individuals of different geographical areas, but also between healthy people who live in the US.

Research shows that the bacteria in the gut communicate with the brain by modulating immune cells and stimulating endocrine cells to produce hormones such as dopamine and serotonin. So a healthy gut will help foster a happy mind, while too much bad bacteria can cause sugar cravings, fatigue, and depressed mood.

The ability of gut bacteria to cause changes in the brain is exemplified by a study where the introduction of Citrobacter rodentium to the gut of mice induced anxiety-like symptoms.

Another example was found in mice who were colonized by the microbe toxoplagandai. After the introduction of the toxoplagandai the mice lost their fear of cats, and while that may sound funny, isn’t wasn’t so good for the mice. So what these studies show is that introducing certain microbes to the gut can cause changes in thinking and behavior.

Gut microbes also have a direct impact on our immune system. If the gut bacteria are healthy, the immune system will be in its optimal shape, but if harmful bacteria dominate your gut, the immune defenses will be challenged.

Probiotics

Probiotics are live, active bacteria that are available in the form of fermented dietary products such as yogurt, sauerkraut, kombucha, and kefir or may be taken as a supplement in liquid or pill form. Probiotics are shown to positive effects on metabolism, mood, digestion, memory, immune response, hormone regulation, and many other benefits.

Good gut bacteria have shown to have a diminishing effect on cortisol which is the stress hormone and an increase in serotonin, which is the happy hormone. This is why probiotics, which increase the number of good bacteria in the gut are now being referred to as “psychbiotics” by some.

In one study, taking probiotics showed an increase in levels of antibodies in the gut, which are an important part of the immune system that protects us from disease. IgA antibody, for example, plays a vital role in keeping the cells of the gut barrier tightly together.

This prevents the entry of the disease-causing bugs into the body and making you sick as well as reducing the risk of the ominous “leaky gut syndrome” in which toxins in the gut enter the bloodstream causing massive inflammation in the body. Leaky gut is caused by eating lots of foods your body has a hard time digesting, which leads to inflammation, and thus a decrease in the integrity gut barrier.

When we take things like probiotics we are adding more good bacteria in the gut, which is beneficial for many reasons such as increased immune system and mood, but these bacteria will get flushed out of the gut after a few weeks so we will need to keep taking them. When we consume prebiotics one the other hand we help to feed the good bacteria we were born with. So really taking both pre and probiotics is the best bet.