The Stress Response

This is the first of a three-part series about the stress response, its opposite, the relaxation response, and how the two processes influence who we are as eaters, our relationship with food, and our relationship with life.


Stress = any real or imagined threat and the response to that threat

We were all born with a stress response to get us through life. It’s what gets us out of bed in the morning and motivates us throughout the day. Optimal arousal levels vary from person to person and situation to situation, which is why something that energizes one person may stress the next, and something that seems easy one day may feel insurmountable the next. Scientists have identified two types of stress – eustress, the good stress that motivates us, and distress, the kind of stress that overwhelms us, clouds our thinking and impairs our judgment. Each of us has a unique optimal stress level, the point just before which eustress turns to distress.

Our stress response evolved as a short-term survival solution, stemming from the time when our ancestors needed to survive their encounters with predators. When we are stressed, our bodies secrete cortisol and adrenaline (epinephrine.) Stress enervates every cell in the body. Pain receptors are dulled temporarily and senses are heightened, blood is diverted from the digestive system to our limbs and head, and the digestive system shuts down so the body can direct its metabolic energy into survival. In a dangerous situation, we have 2-4 minutes to either fight the predator or get away. After that time, our body chemistry is designed to return to homeostasis, meaning if we survive the threat, we can relax and return to our pre-stress activities. (*See below for a more detailed explanation of the physiology of the stress response.)

The stress response is appropriate and natural under survival conditions, in motivational situations and in the normal course of life. It is problematic when it is long term and/or self-chosen. While cortisol is an important and helpful part of the body’s response to stress, it’s important that the body’s relaxation response be activated so the body’s functions can return to normal following a stressful event. Yet in our current high-stress culture, the body’s stress response is activated so often that the body doesn’t always have a chance to return to normal, resulting in a state of chronic stress. And the brain doesn’t distinguish between a real and imagined stress, so the physiologic stress response is activated when we have a bad day, when we think toxic thoughts, and when we judge ourselves harshly. Our bodies pump out cortisol almost constantly, which alone can wreak havoc on our health.

Here are 15 effects of stress and prolonged elevated cortisol you may not know:

  1. Four times less blood flow to the digestive system
  2. Decreased secretion of growth and thyroid hormones, slowing down metabolism
  3. Increased secretion of cortisol, which increases blood sugar and dampens insulin efficiency. If unresolved, excess insulin signals your body to store excess sugar as fat.
  4. Impaired mitochondrial function
  5. Excretion of all minerals and water soluble vitamins
  6. Decreased oxygen uptake, slowing down all body systems
  7. Increased inflammation and oxidative stress
  8. Decreased thermic efficiency impairing your ability to burn calories
  9. Suppressed immune system
  10. Impaired cognitive function
  11. Decreased bone density
  12. Decrease in muscle tissue
  13. Blood sugar imbalances
  14. Higher blood pressure
  15. Increased abdominal fat, including its associated problems (heart attacks, stories, metabolic syndrome, higher “bad” cholesterol (LDL), lower “good” cholesterol (HDL)


*The Physiology of Stress

The stress response begins in the amygdala, the emotional processing area of the brain. The amygdala interprets images and sounds, and if it perceives danger, it sends a distress signal to the hypothalamus, the command center part of the brain. The hypothalamus communicates with the rest of the body through the autonomic nervous system, which controls such involuntary body functions as breathing, blood pressure, heartbeat, and the dilation or constriction of blood vessels and the small airways in the lungs. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system revs us up, triggering the fight-or-flight response and providing the body with a burst of energy so that it can respond to perceived dangers. Its opposite, the parasympathetic nervous system slows us down, promoting the “rest and digest” response that calms the body down after the danger has passed.

When the amygdala sends a distress signal, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. The adrenals respond by pumping the hormone epinephrine (also known as adrenaline) into the bloodstream. As epinephrine circulates through the body, the heart beats faster than normal, pushing blood to the muscles, heart, and other vital organs. Pulse rate and blood pressure go up. Breathing becomes more rapid, and small airways in the lungs open wide to take in as much oxygen as possible with each breath. Extra oxygen is sent to the brain, increasing alertness. Senses become sharper. Meanwhile, epinephrine triggers the release of blood sugar (glucose) and fats from temporary storage sites in the body flooding the bloodstream, supplying energy to all parts of the body.

These changes happen quickly, out of our awareness. The process is so efficient that the amygdala and hypothalamus start this cascade of hormones even before the brain’s sensory centers can process fully what is happening, which is why we can spring into action if we need to without thinking things through. 

If the brain continues to perceive danger as the initial surge of epinephrine subsides, the hypothalamus activates the second component of the stress response system, the HPA axis (hypothalamus, pituitary and adrenal glands). The hypothalamus releases CRH (corticotropin-releasing hormone), prompting the pituitary gland to release ACTH (adrenocorticotropic hormone). ACTH prompts the adrenal glands to release cortisol, keeping the body revved up and on high alert. Cortisol prepares the body for fight-or-flight by flooding it with glucose, supplying an immediate energy source to large muscles. At the same time it inhibits insulin production in an attempt to prevent glucose from being stored so it can be used immediately. Cortisol narrows the arteries while epinephrine increases heart rate, both of which force blood to pump harder and faster. When the threat passes, cortisol levels fall. Then the parasympathetic nervous system dampens the stress response allowing the body’s systems to return to pre-stress levels.