The bacteria in your gastrointestinal tract (gut) is often referred to as your second brain, and for a good reason. Inside your stomach is a very complex, multi-organism microbiome that consists of not only your cells but also various bacteria that help you digest your food. The most prominent bacteria are Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria, but there are many more as well. The effects of these bacteria are currently in research, but recent scientific studies have discovered that these bacteria are not only beneficial but a necessity for survival.

The bacteria in your gut can make your basic life functions easier and overall happier in general. A study published in The Journal of Neuroscience conducted an experiment where they studied germ-free mice (in the gut) compared to mice containing bacteria. These germ-free mice displayed an exaggerated response to restraint stress and anxiety-related behaviors, which affected the overall well-being of the rat.

What makes it much more interesting is that gene expression of a key protein regulating neuronal plasticity and cognition was observed to have decreased, whereas a control group of normal mice with gut bacteria showed the necessity of such bacteria for survival. When the scientists re-introduced the bacteria in the gut, these effects were somewhat able to be reversed and symptoms, including neuronal cognition, were mediated; however, not all the mice with reintroduced gut bacteria were seen to recover from the symptoms and continued symptoms were especially prominent for mice that were not in early childhood/adolescence.

Scientists then applied this newly found information and analyzed human fecal matter. They began to see the effects of various dietary choices and how it affects your brain. The current focus is on probiotics, which is a $20 billion industry in today’s market, and it is promoted widely as healthy. But why?

The testing of gastrointestinal tract bacteria and probiotics is relatively early in its studies, but there are specific strains that have been proven to impact your gut microbiome positively. Additional studies of groups given probiotics against groups given a placebo in hospitals measured for mood and cognition. Using the total Hospital Anxiety and Depression Scale, the researchers saw that the probiotics group had a higher percentage decrease versus the placebo group. These tests were based on the mood, something that is not quantifiable. However, suggested evidence tells us that probiotics help with increased mood and further, larger clinical trials are being conducted to find more evidence.

Manipulation of the microbiome in your gut is utilized for many applications, including chronic diseases and illnesses. Hepatic encephalopathy, a symptom of a chronically diseased liver, causes patients to have complications with cognitive function and patients treated by gastrointestinal tract bacteria manipulation. Antibiotics are given to help the patients because their diseased livers cannot process the gut bacteria metabolites. Reducing the bacteria that cause these metabolites to mediate the problem results in the disappearance of these metabolites, thus improving cognitive function. The bacteria microbiome here have a direct effect of the patients’ function, displaying how your gut bacteria controls your brain.

Evidence in mice suggests that gastrointestinal tract microbiome may be not only necessary for yourself right now but also crucial for early brain development. Right after birth, the newborn is introduced to many different microorganisms, and this early microbiome is essential for the development of the early brain. A 2010 study, Normal gut microbiota modulates brain development and behavior, tested mice with different microbiome organisms to see the effects. Germ-free (GF) mice were tested versus normal mice in anxiety and exploratory activity.

Mice were tested to see if the absence of gut bacteria would affect the maturation of the brain of the mice. Key proteins were found missing from the GF mice, and later those mice experienced anxiety behaviors. Interestingly, proteins for the development of synapses were not expressed as much, which seems to lead to a long-term effect on the developing mice in motor control and anxiety. Results such as “elevated Noradrenaline (NA), Dopamine (DA), and 5-HT Turnover in the Striatum” appeared to cause the anxiety-like behaviors. In other words, mice without a bacterial microbiome saw anxiety-like behaviors due to changes in the neuronal chemistry inside the brain. This suggests that in humans early childhood, gut microbiome is important for the development of the synapses of the brain and controls the brain through gene expression leading to protein expression.

Your health, mood, and well-being may be in fact due to the microbiome that lays inside your gastrointestinal tract. Studies observed that mice gut bacteria cause anxiety-like symptoms. Eating probiotics have shown to be beneficial, but further research is still necessary. For now, understand the correlation between what you eat affects how you feel, and that your stomach bacteria plays a significant role in your health.