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Stress affects us all. Every psychological state we experience has a corresponding physiological state. With the recent knowledge of the microbiome it is easier to comprehend how stress can disrupt the gut and how, in turn, the gut can affect our moods and emotions. The key to this new understanding is a complex network called the gut-brain axis, which has an enormous impact on the health of our body and mind.

The gut-brain axis consists of a number of major systems in the body including the nervous system, enteric nervous system or ENS, endocrine system, enteric endocrine system, immune system, and the gut bacteria. During a stress response, these different systems can clash with each other.

The brain has many different ways of disrupting the gut during stress. The most direct way is by sending signals through nerves to the digestive system. The most important nerve for the health of gut is the vagus nerve, which starts in the brain and branches to the throat, heart, lungs, and eventually, makes its way to the GI tract.

The brain can also disrupt the gut through hormones and chemical messengers. During stress, the brain triggers the adrenal glands to release the stress hormone cortisol, which goes into the bloodstream and affects the gut and gut bacteria. It can, for example, increase intestinal permeability, which results in a leaky gut. It can also shut down the activity of the gut immune system and secretion of cytokines (70-80% of the entire immune system is located in the gut walls).

What is extremely interesting is that the communication between these different systems is bidirectional. The gut bacteria use the vagus nerve to communicate with the brain, and can also produce a wide variety of chemical messengers, including neurotransmitters and hormones, which can enter the bloodstream and affect the brain as well as other systems in the body.

One recent brain imaging study at UCLA showed that women react differently to stimuli depending on the type of bacteria they have in their gut. The same researchers had previously shown that diet could affect the brain. They gave subjects either a psychobiotic (a probiotic mixture that is used for mental health) or a placebo. They then showed the subjects images of frightened faces while measuring brain activity. The subjects taking the placebo showed a normal stress response with specific areas of the brain responsible for emotions being activated. Subjects receiving the psychobiotic showed a reduced stress response in these same areas of the brain.

One part of the gut-brain axis that most people are not familiar with is the enteric nervous system (ENS). It acts as a “second nervous system” inside their gut. The ENS consists of 500 million nerve cells—fewer than the brain’s nearly 100 billion nerve cells, but comparable to the entire central nervous system of a small mammal.

The ENS monitors and regulates the gut, sending signals to our brain that identify every detail of digestion. The ENS produces more than 30 neurotransmitters, many of which are the same as the neurotransmitters in the brain.

Stress disrupts the activity in the ENS. Researchers have suggested that one way stress does this is by altering the production of specific neurotransmitters, such as serotonin. Gut bacteria play a critical role in the early development of the ENS, and have many ways of influencing the activity of cells in the ENS, including modifying serotonin production.

Traditional systems of medicine, including Ayurveda, contain a wealth of time-tested procedures to improve the state of our gut and reduce stress. I have studied the Transcendental Meditation (TM) program for over fifty years, and it is clear from this research that this particular meditation technique has a remarkable ability to reduce the effects of stress. One of the studies published on TM reports a 48% reduction in heart attacks, strokes, and deaths in the TM group as compared to randomly matched controls. Over $25 million in grants from the National Institutes of Health have supported research on the beneficial effects of TM on cardiovascular disease. Ayurveda also uses many different diets and herbs to reduce the effects of stress on the gut. I am very excited about the possibility of studying how the combination of Transcendental Meditation and Ayurvedic diet and herbs, can help reduce the deleterious effects of stress and improve the state of our gut and gut bacteria.



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