Mental Health and Digestion: A Critical Piece of the Mental Health Puzzle

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Imagine that in ten minutes you’re about to give a speech to an auditorium filled with hundreds of people. You’ve practiced your speech but there are still some sentences that you stumble over. As you wait backstage, your stomach is full of butterflies and you feel your palms sweating. What if you get on stage and freeze? What if they laugh? What if... One of the backstage workers comes in with a bag of fresh fast food, and as the smell reaches your nose, a wave of nausea comes over you.

While you may not have experienced this exact scenario, you’ve probably been in a situation when you were feeling nervous or upset and this caused you to feel sick to your stomach or you suddenly lost your appetite. This is just one example of the complex and intricate relationship that exists between the brain and the digestive system.

A fascinating part about this relationship is that it’s not only the brain that affects our digestion; the digestive tract also sends information to the brain and can influence brain function via other avenues as well.(1)

It goes both ways:

The brain’s impact on digestion

When we feel anxious or stressed, this activates the “fight or flight” part of our nervous system (known as the sympathetic nervous system). In this sympathetic state, the body’s resources are dedicated to tasks required for immediate survival: using our muscles and brains to react quickly and get us out of danger. This is an evolutionary adaptation so that we can handle life-or-death situations like being faced with a sabre tooth tiger. The sympathetic nervous system is critical in these moments.

The problem occurs when we get “stuck” in sympathetic mode. As illustrated in the example of giving a speech, digestion is NOT a priority when we are in stressful situations. Our digestive system effectively shuts down temporarily, and will restart once we are relaxed again, when the “rest and digest” (parasympathetic) part of the nervous system can be active.(2) In this day and age, many individuals in modern times are anxious or stressed so regularly, that their nervous system has difficulty getting out of sympathetic mode and into parasympathetic mode. This means that when they eat, their digestive system is not fully digesting foods or absorbing nutrients. In order to properly digest, we need to learn to be relaxed before we eat.

Another, more obvious impact of our brain on digestive health, is the way eating habits change with our moods. Some people tend toward overeating and high carbohydrate foods when feeling stressed or down. For others, they will lose their appetite, or intentionally under-eat in order to cope. These habits are easier to identify, but can often be challenging to shift.

How the gut influences the brain

Interestingly, gastrointestinal health has effects on the brain through several means, including the gut microbiome, neurotransmitters, and nutrient availability.

The intestinal microbiome has been an expanding area of research for many years now. Studies have shown that unhealthy bacteria (and/or lack of good bacteria) in the intestine are tied to an array of conditions. It is now known that unhealthy bacteria can influence mental health, even being a contributing factor to depression.(3) This is in part because when certain “bad” bacteria are present in high amounts, they can trigger an immune response and inflammation throughout the body. When inflammation affects the nervous system, it begins to change the way the brain produces molecules such as serotonin, which help to regulate emotion.

If there is a gastrointestinal problem that impairs nutrient absorption, there may be an insufficient supply of critical vitamins and minerals to the brain. This can impair the normal production of neurotransmitters, thereby altering mood