We often think of bacteria as something dirty and dangerous, something that has the potential to cause us harm; and, while this is true in some cases, bacteria are fundamental to human existence. In fact, “single-celled organisms — mostly bacteria — outnumber our own cells 10 to one, and most of them make their home in the gut.” This gut bacteria make up what is known as the “microbiome”: a massive collection of nonhuman cells within the body that plays an integral role in our physical health. New research reveals, however, that our gut might do much more than that. In fact, our gut might have a significant influence on our brain functioning.
Stephen Collins of McMaster University in Hamilton conducted a rodent study that suggested some unprecedented conclusions on this topic. He took samples of gut bacteria from bold mice, and placed it in the guts of anxious mice, and vice versa. The results were astonishing: “bold mice became timid when they got the microbes of anxious ones,” while anxious mice became more fearless. When researchers looked the mice’s chemistry, they found correlative changes in “a part of the brain involved in emotion and mood, including increases in a chemical called brain-derived neurotrophic factor.”
Other studies have replicated these findings. This is important because it illustrates that “in laboratory mice, some seemingly intrinsic characteristics are driven not solely by the animals themselves, but also by microbes inhabiting the gut.” An additional study found that when mice who exhibited “behaviors similar to some of the symptoms of autism in humans,” were administered probiotics, their symptoms greatly disapproved, and in some cases, disappeared altogether.
While human studies on this link between gut bacteria and brain health are nascent, there are some interesting findings. One study at UCLA conducted a study in which they gave one group of women yogurt with probiotics, another group a similar product, but without probiotics, and the last group with no food product. Functional MRI’s were used to detect brain activity when the women were at rest and when they participated in an emotion-recognition test. They found that not only did the women who consumed probiotic yogurt “[show] a decrease in activity in … the insula … and the somatosensory cortex during the emotional reactivity task,” they also, “showed greater connectivity between a key brainstem region known as the periaqueductal grey and cognition-associated areas of the prefrontal cortex,” while at rest. This essentially means that they experienced less activity in areas of the brain related to anxiety and emotional reactivity, compared to those women who didn’t consume probiotics.
Also of note is the fact that the gut doesn’t just influence the brain — the brain can have a significant impact on the gut. “Numerous studies, for example, have shown that psychological stress suppresses beneficial bacteria,” which can render “the host more vulnerable to infectious disease and triggering a cascade of molecular reactions that feed back to the central nervous system.”
There are several pathways in which the gut and brain communicate. For starters, there is the vagus nerve, “which runs all the way from the brain to the abdomen.” Furthermore, these two regions of the body communicate via chemical messengers known as neurotransmitters. “Gut bacteria … produce hundreds of neurochemicals that the brain uses to regulate basic physiological processes as well as mental processes … For example, gut bacteria manufacture about 95 percent of the body’s supply of serotonin, which influences both mood and GI activity.”
Much research still needs to be done in order to understand the link between brain health and the microbiome. However, early research that suggests a healthy gut leads to a healthy brain (and vice versa) is promising — yet more evidence in favor of a balanced and healthy diet.