A Gut Feeling

Symptoms of anxiety and depression may be related to the microbiota in our gut.

“You knit me together in my mother’s womb. I praise you, for I am fearfully and wonderfully made” (Ps. 139:13-14).

In this psalm, attributed to David, he notes that our bodies, minds and souls are things of wonder and complexity. In this age of rapidly advancing knowledge, scientists are finding out just how accurate David’s description of our bodies is. We are discovering complex connections undreamed of even 15 years ago!

Consider the strange link between our brain and the millions of microbiota living in our digestive system. It appears that these independent bacteria and other microorganisms can in some manner influence brain function and mood. In 2004 scientists found that mice raised germ free (with no gut bacteria) showed a larger physiological response to stress than mice with normal gut bacteria, suggesting that normal gut functioning results in better responses to stressful situations. Other germ-free mice received a fecal transplant (and so new microbiota) from humans suffering from major depressive disorders. These mice exhibited more symptoms of anxiety than did germ-free mice who received fecal transplants from non-depressed humans. This suggests that the brain-driven symptoms of anxiety and depression may be related to the microbiota in our gut. Scientists are currently trying to better understand these possible interactions. Maybe there is a place for gut feelings.

Humans with autism often have gastrointestinal problems. Both their social interactions and their digestive system seem not to be functioning optimally. Autism is often diagnosed at about two to three years of age, the very same age at which an individual’s distinctive gut flora become established, suggesting some linkage.

At this point, the direction of the relationship between the gut, the brain and our behaviour is not clear; brain abnormalities may be a cause of gut differences, or problems in the gut may cause changes in the brain. Or the suggested relationship may be bidirectional or just coincidence. Naturally, given the severity of the mental health issues today, a lot of active research is exploring the relationship between the gut and the brain.

Cancer cells & neurons
More recently, another unexpected interaction has emerged. It appears there may be a relationship between neurons and cancer. Cancer cells seem to promote the growth of neurons, which naturally grow out to make connections, but preferentially make extensions into the centre of cancer cells, and in turn these neural extensions increase the growth rate of cancer. When mice spinal nerve cells were put in a dish next to human prostate cancer cells, there was a sort of dance between the two types of cells. The cancer cells turned neural growth in their direction, and when the spinal nerves reached the cancer cells and grew into them, the growth of the cancer was increased. So the cancer has an effect on the neurons, and in turn the neurons do something that promotes cancer growth (which is not a good thing).

Some scientists have suggested this neural–cancer connection may be part of the explanation for why chronic stress seems to promote the progression of cancer. Cancer cells are very good at using the body’s natural processes to promote their growth. Blood capillaries are routed into the tumor by the cells, and the extra resources provided by the capillaries help the tumor survive. Knowing this about blood vessels has given doctors specific medicines that prevent rerouting of capillaries and thus increase the survival of patients. If cancers are using nerve processes in a similar manner, there may be new classes of drugs available to treat cancer.

The complexity of our bodies will keep scientists busy for generations. And as we discover more of these strange connections, we can both better appreciate David’s words in Psalm 139 and also have hope for new ways to treat some of our serious medical conditions.


  • Rudy Eikelboom is a Professor of Psychology, at Wilfrid Laurier University, who has emerged from the dark side of the University after being department chair for 9 years and now teaches behavioural statistics to graduate and undergraduate psychology students. His retirement looms and he is looking forward to doing more writing on the implications of modern science for our Christian faith. Currently, he serves as a pastoral elder at the Waterloo Christian Reformed Church.

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