Gut Check

We’ve all had a “gut feeling” before. That sensation right below your ribs that says “go for it” or “don’t you dare!”. Though the saying “listen to your gut” might seem more like a metaphor than reality, recent research from neurobiologists suggests that your gut does in fact have a lot to say.

Our guts contain over 500 million neurons, which collectively are known as the enteric nervous system (ENS). The ENS and the brain are in constant communication- the stomach telling the brain it’s full, the brain telling the stomach to get to work when we are about to eat, etc. The interaction between the ENS and the brain, known as the gut-brain axis, is also the reason we sometimes feel our emotions in our bellies. For example, the feeling of butterflies you might get when falling in love is the product of stress hormones being passed from the brain to the gut, where they activate sensory receptors resulting in that exciting fluttery feeling. Similarly in other stressful situations, like right before you have to give an important presentation, clusters of ENS neurons in the esophagus can be overstimulated by signals from the brain causing the esophagus to tighten and resulting in the experience of “choking” under pressure.

The influence of the brain on our guts has been established scientifically for quite some time, and is probably intuitively apparent to everyone, but in recent years scientists have begun to discover that our guts actually play a much bigger role in our human experience than previously imagined.

It turns out that our intestines are home to a diverse community of bacteria known as the microbiome. These little gut bugs (of which the human intestines contain about 100 trillion!!) are important for functions like digestion, nutrient absorption, and immune system function, but they also have a huge impact on our mood, behavior, and cognitive abilities; especially when it comes to stress and depression.

Much of what is currently known about the influence of the microbiome on brain and behavior comes from animal studies. For example, a 2004 study that compared germ-free mice (that is, mice born without a microbiome) to a control group of mice (with regularly colonized guts) showed that the germ-free mice had an exaggerated stress response compared to the controls. Importantly, when young, germ-free mice were introduced to a particular strain of gut-bacteria, their stress response was diminished. Studies using a similar design have shown that germ-free mice also express memory deficits, like object recognition and working memory, and social-cognitive deficits, such as social avoidance, compared to control mice.

Further evidence for this critical role of the microbiome has been found by tinkering with the existing microbiome either by introducing probiotics or through fecal transplants (which is exactly what you think it is: poop swap). A number of studies using probiotics have found that introduction of particular strains of bacteria effectively alleviate depressive-like behaviors. Conversely, introducing the microbiome of a depressed person into the gut of a rat via fecal transplant can cause the rat to become depressed.

Though much of this kind of research has been done in animal models, these findings seem to be true human subjects as well! For example, the use of probiotics in humans has been effective for alleviating symptoms of depression, improving cognition, and reducing stress levels. The gut microbiome also appears to have an impact on social behaviors in humans. Human studies using the fecal transplant method have shown that children with autism spectrum disorder (typically characterized by social-cognitive deficits) will become more social when the microbiome of a typically-developed child is introduced to their system.

This field of research is relatively new and there is certainly much left to be discovered about the function of the human microbiome and mechanisms by which it affects our brains and behaviors, but the evidence thus far suggests that there are some gut-bugs that promote positive mood, clear thinking, and prosocial behaviors and others that don’t. Fortunately, we have the power to cultivate and nurture the good ones by making sure our diets are beneficial for our bugs. The current consensus seems to be that diets high in dietary fibre, fruits, vegetables, and fermented foods help the good bugs proliferate and triumph over the bad ones. The best part is that it doesn’t seem to take very long to start noticing changes. Some studies have shown alterations in the microbiome composition after only 10 days of eating well! Adding probiotics to your diet might also be a smart choice. So far, the strains Lactobacillus and Bifidobacterium infantis seem to be the most beneficial for alleviating symptoms of depression and anxiety, so be sure to check the label to see what you’re getting.

Though there isn’t much evidence to support the role of our guts in providing the wisdom and insight we typically associate with a “gut feeling”, we now understand that our guts play a big role in how we think and feel and, even better, we can use this information to improve the quality of our everyday lives. Keep listening to your gut, but don’t forget to take good care of it.