Meet Your Second Brain: Your Gut
Can you relate to the experience of having butterflies in your stomach?
Have you ever relied on your “gut-instinct” or “gut-feeling” when making a decision?
There’s actually tangible scientific proof to support these popular metaphors.
Research has often referred to your gut (your stomach and intestines) as your “second brain,” and it’s with good reason.
When you grew in your mother’s womb, your gut and your brain were actually formed from the same fetal tissue and will continue their special bond throughout your entire life.
Millions of nerves and neurons run between your gut and brain. This line of communication between the gut and nervous system is called the gut-brain axis.
Neurotransmitters and other chemicals produced in your gut also affect your brain.
For example, when most people eat carbohydrates they get a “feel-good sensation” shortly afterward. This is because carbohydrates stimulate the release of insulin from the pancreas and allow tryptophan to enter the brain more easily. Tryptophan is the protein used to make serotonin (9). This is often followed by feelings of happiness, well-being, and sleepiness.
Scientists are finding that the bacteria in your gut (the gut microbiome) may have an impact on your cognitive function and possibly its decline (8). Research has proven that disturbances to this system are linked to a wide range of health ailments, including depression, anxiety, addiction, eating disorders, inflammatory gastrointestinal disorders, and obesity.
When we want to heal the brain, we may need to look into our gut for clues.
A Brief Anatomy Lesson: The Enteric Nervous System
Hidden in the walls of the digestive system, the “brain in your gut” is called the enteric nervous system (ENS). And it’s not so little. The enteric nervous system is two thin layers of more than 100 million nerve cells lining your gastrointestinal tract from esophagus to rectum.
Simply speaking, the word enteric means “intestines.” You may have read the phrase “enterically coated” on your bottle of fish oil. This means that the coating will not break down before the capsule makes it to your small intestine; saving you fishy burps.
We are well aware of the nervous system and how it sends signals and messages throughout the body. The nervous system is made up of the following:
- Central nervous system – brain & spinal cord
- Peripheral nervous system – everything outside of the brain & spinal cord
- Somatic nervous system – voluntary control of movements such as moving and facial expressions
- Autonomic nervous system – involuntary control such as heartbeat and breathing
- Sympathetic nervous system – flight or fight, increases heart rate & respiration, stressful situations
- Parasympathetic nervous – rest and digest, slows heart rate & respiration, regulates digestion
- Enteric nervous system – the gastrointestinal tract (GI tract)
The enteric nervous system is well-studied, but there are many complex questions yet to be answered (2,4). Remember from above when we discussed how the foods you eat can influence your emotions? The GI tract has the ability to sense the presence of foods, changes in the gut microbiome, and potential bacteria that could harm your body (3).
The enteric nervous system acts independently from the other parts of the body moving food through digestion, sending signals to the brain, and releasing hormones to tell the other parts of the body how to respond. Gut health is important because, as you can see, it can influence the body in different ways.
Poor Gut Health Can Lead to Neurological and Neuropsychiatric Disorders
Poor gut health has been implicated in neurological and neuropsychiatric disorders.
Disturbances in gut health have been linked to multiple sclerosis, autistic spectrum disorders, and Parkinson’s disease. This is potentially related to pro-inflammatory states elicited by the imbalance of the microbes inside the gut. Additional connections between age-related gut changes and Alzheimer’s disease have also been made (8).
Further, there is now research that identifying depression as an inflammatory disorder mediated by poor gut health (8). In fact, multiple animal studies have shown that manipulating the gut microbiota in some way can produce behaviors related to anxiety and depression.
Our brain’s health, which will be discussed in more depth in a later blog post, is dependent on many lifestyle choices that mediate gut health; including most notably diet (i.e., reduction of excess sugar and refined carbohydrates) and pre and probiotic intake.
Can You Balance The Gut-Brain Axis?
Yes! Surprisingly, balancing the gut-brain axis can easily be managed. You have to be aware of various lifestyle factors such as the following:
- Physical Activity & Exercise – The benefits of exercise for both managing weight and improving brain function are well researched (Morgan). However, exercising can also improve your gut health in significant ways, which can be beneficial for the Gut-Brain axis (1)
- Sleep – Sleep is extremely important for all aspects of your life. While you sleep you can essentially “recharge” your body to ensure that it is functioning optimally. Losing sleep can affect hormones and chemicals in the gut and brain that influence decision-making, weight, and attitude (7).
- Nutrition – The foods you eat influence your gut health as well as your cognitive health. Therefore, eating foods low in processed, refined sugar and high in vitamins, minerals, and fiber will help improve gut health and reduce inflammation.
What Foods Help the Gut-Brain Axis?
A few groups of foods are specifically beneficial for the gut-brain axis.
Here are some of the most important ones:
- Omega-3 fats: These fats are found in oily fish and also in high quantities in the human brain. Studies in humans and animals show that omega-3 fatty acids can increase good bacteria in the gut and reduce the risk of brain disorders
- Fermented foods: Yogurt, kefir, sauerkraut, and cheese all contain healthy microbes such as lactobacilli. Fermented foods have been shown to alter brain activity.
- Polyphenol-rich foods: Cocoa, green tea, olive oil, and coffee all contain polyphenols, which are plant chemicals that are digested by your gut bacteria. Polyphenols increase healthy gut bacteria and may improve brain function.
- Tryptophan-rich foods: Tryptophan is an amino acid that is converted into the neurotransmitter serotonin. Foods that are high in tryptophan include turkey, eggs, and cheese.
Millions of nerves and neurons run between your gut and brain. The gut-brain axis refers to the physical and chemical connections between your gut and brain. Neurotransmitters and other chemicals produced in your gut also affect your brain.
Balancing the gut and the brain is important for your physical and mental health.
By altering the types of bacteria in your gut, it may be possible to improve your brain health. Omega-3 fatty acids, fermented foods, and other polyphenol-rich foods may improve your gut health, which may benefit the gut-brain axis.
- Evans, C. C., LePard, K. J., Kwak, J. W., Stancukas, M. C., Laskowski, S., Dougherty, J., … & Antonopoulos, D. A. (2014). Exercise prevents weight gain and alters the gut microbiota in a mouse model of high fat diet-induced obesity. PloS one, 9(3), e92193.
- Gershon, M. D., & Wade, P. R. (1993). Enteric nervous system. Current Opinion in Gastroenterology, 9(2), 246-253.
- Goyal, R. K., & Hirano, I. (1996). The enteric nervous system. New England Journal of Medicine, 334(17), 1106-1115.
- Grundy, D., & Schemann, M. (2005). Enteric nervous system. Current opinion in gastroenterology, 21(2), 176-182.
- Morgan, W. P., & Goldston, S. E. (2013). Exercise and mental health. Taylor & Francis.
- Murri, M., Leiva, I., Gomez-Zumaquero, J. M., Tinahones, F. J., Cardona, F., Soriguer, F., & Queipo-Ortuño, M. I. (2013). Gut microbiota in children with type 1 diabetes differs from that in healthy children: a case-control study. BMC medicine, 11(1), 46.
- Schmid, S. M., Hallschmid, M., JAUCH‐CHARA, K. A. M. I. L. A., Born, J. A. N., & Schultes, B. (2008). A single night of sleep deprivation increases ghrelin levels and feelings of hunger in normal‐weight healthy men. Journal of sleep research, 17(3), 331-334.
- Sherwin, E., Dinan, T. G., & Cryan, J. F. (2018). Recent developments in understanding the role of the gut microbiota in brain health and disease. Annals of the New York Academy of Sciences, 1420(1), 5-25.
- Wurtman, R. J., & Wurtman, J. J. (1996). Brain serotonin, carbohydrate-craving, obesity and depression. In Recent advances in tryptophan research (pp. 35-42). Springer, Boston, MA.