Have you ever wondered why your gut feels out of whack when you’ve had a tough week? Although you’re not aware of it, your gut and your brain “talk” to each other all day, every day. The connection between the two is so close that it’s known as the gut-brain axis, so when your brain screams, “I’m stressed!”, your gut can’t help but respond.
Being under constant stress can create a cycle that leads to poor gut health and ongoing symptoms. But when you understand how stress impacts your gut, you can learn to control the triggers and give your body the tools to support optimal digestion.
How does stress affect gut health?
Stress is a complex reaction involving just about every system in your body. When one system is triggered, it sets off a series of reactions that can continue in a repeating cycle stress is prolonged.
Scientists are still uncovering the details of exactly how this cycle affects gut health, but current research highlights several factors:
- Nervous system responses
- Changes in the gut microbiome
- Inflammation
- Hormone production and balance
- Neurotransmitter production
What’s the role of the nervous system in the gut?
The autonomic nervous system is the part of your nervous system responsible for controlling digestion and other involuntary bodily functions—the ones you don’t have to consciously think about. It contains three divisions, each of which interacts with the gut in different ways:
- The enteric nervous system (ENS) is located in the gut and contains over 100 million neurons as well as cells called enteroendocrine cells, which make hormones that aid in digestion.
- The sympathetic nervous system (SNS) kicks in when you’re scared or stressed and produces what’s commonly known the “fight-or-flight” response. The SNS sends signals that tell your body to increase your heart rate, boost blood pressure and break down stored glucose for a quick burst of energy. It also slows down or pauses other processes like digestion so your body can put all its resources toward dealing with or avoiding the perceived threat.
- The parasympathetic nervous system (PNS) counteracts the SNS by prompting your cardiovascular system to relax after a stressful situation is over, a response known as “rest and digest.” In the gut, the PNS stimulates the digestive process at mealtimes by increasing the secretion of saliva and gastric juices and prompting gut muscles to contract.
One long nerve called the vagus nerve connects the ENS to the brain and brings these processes together. The vagus nerve makes up 75% of the PNS and extends from your brainstem to your abdomen. It also sends fibers into organs throughout your digestive system—including your esophagus, stomach, pancreas, small intestine and colon—to control processes like muscle contractions and hormone release.
How does stress affect the gut microbiome?
What scientists know about stress and the microbiome comes mostly from studies on rodents. The studies suggest that stress can reduce levels of beneficial bacteria like Lactobacillus and Bifidobacterium and increase potentially pathogenic bacteria like Clostridium. How long it takes for the shift to happen—and the amount of recovery time the microbiome needs after stress resolves—appears to differ between individuals.
If the same changes happen in the human gut during stress, it could lead to a reduction in the byproducts that come from beneficial bacteria. These compounds include short-chain fatty acids (SCFAs), which microbes release when they break down fiber from the food you eat.
Can stress damage your gut?
The combination of a sympathetic stress response, an increase in pathogenic bacteria, and a lack of SCFAs may damage your gut tissue. Some studies show a connection between lower SCFA production and increased inflammation, and the SNS activates pro-inflammatory immune cells when you’re under stress. Stress on the autonomic nervous system may also affect how well you gut produces the mucus that protects gut tissue and leave your gut tissue more vulnerable to inflammation.
Inflammation can cause the tight junctions between cells in your gut to open up, a condition known as increased permeability or “leaky gut.” These junctions are meant to keep the contents of your gut separate from your bloodstream, but when they get leaky, bacteria and food particles can pass through and trigger immune responses, resulting in more inflammation.
Why are hormones important to understanding how stress affects gut health?
The enteroendocrine cells in the ENS make at least 30 different hormones, chemical messengers that help the nervous system and gut communicate by bonding with special receptors on cell surfaces to trigger responses. These include:
- Gastrin to secrete stomach acid (HCl)
- Cholecystokinin to stimulate gallbladder contractions and prompt the release of enzymes from the pancreas
- Glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and motilin to prompt digestive secretions, help food empty from the stomach, move food through the digestive tract and promote a feeling of fullness
- Glucose-dependent insulinotropic polypeptide (GIP) to stimulate insulin secretion aid fat digestion
- Somatostatin to regulate the release of other digestive hormones
What’s the connection between gut health and neurotransmitters?
Your gut also produces neurotransmitters that have functions in both the gut and the brain, including:
- Serotonin
- Dopamine
- Acetylcholine
- Norepinephrine
- Gamma aminobutyric acid (GABA)
These neurotransmitters regulate mood, stress, pleasure, motivation and calmness, and their levels may depend on the balance of microbes in your gut. Some neurotransmitters are produced by a type of enteroendocrine cells called enterochromaffin cells, but the production and breakdown of others is regulated by compounds your gut microbes make, including SCFAs.
SCFAs can bind to receptors in the ENS, which then transfer signals to the brain. SCFAs may also interact with genes involved in neurotransmitter production and could play a role in controlling levels of stress hormones. Anything that affects SCFA levels, including stress, may interfere with your body’s ability to make and regulate neurotransmitters.
What about the HPA axis? What role does it play in stress and gut health?
The hypothalamus-pituitary-adrenal (HPA) axis lies at the root of the stress response. The hypothalamus is an organ in your brain that controls the release of hormones, including those involved in stress and hunger. These hormones signal the pituitary gland, a small gland below the hypothalamus, to send additional hormones to your adrenal glands and trigger the last step in the stress response.
Located on top of your kidneys, the adrenal glands release stress hormones like cortisol that activate the sympathetic nervous system. When cortisol binds with receptors in your gut, it increases permeability, slows down your rate of digestion, and possibly contributes to disruptions in your microbiome.
How can I manage stress to improve my gut health?
Short bursts of stress aren’t likely to cause lasting problems in your gut, but prolonged, chronic stress keeps your HPA axis and sympathetic nervous system active constantly, which can make your gut health worse over time.
To break the cycle, consider lifestyle practices that help calm your system and prepare your body and mind for optimal digestion:
Don’t eat on the go.
Your brain activates the digestive process the moment you think about food and continues preparing your body to eat as you make your meal. Slowing down to cook instead of grabbing takeout as you rush between activities gives your body the chance to enter parasympathetic mode before you take your first bite.
Learn to plan and prioritize.
In her book, Digestive Wellness, Elizabeth Lipski, Ph.D., suggests making time in your schedule for the inevitable interruptions that come as a regular part of life. Giving yourself margin for the unexpected ensures you still have the space to eat without rushing. Try to plan meals in advance to save time on shopping and preparation so you can enjoy a stress-free time at the table even when you’re busy.
Identify negative thought patterns.
Lipski also notes that the way you think can contribute to stress. She suggests actively paying attention to your thoughts, noting any negative cycles, and working to reframe doubt or self-criticism into positive statements. This includes replacing patterns of using food to “reward” or “punish” yourself with habits or traditions that encourage you to associate food with enjoyment instead of anxiety.
Refresh your mind and body regularly.
Getting enough exercise and sleep helps reduce stress. When you exercise, your body releases hormones called endorphins that boost your mood. Adequate sleep gives your brain time to rest and process the previous day so you can wake fully refreshed instead of feeling overwhelmed.
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