Kelsey Graham by Kelsey Graham

Last updated September 21, 2023 (originally published April 25, 2019) 

You’ve likely experienced the physiological effects of stress—sweaty palms, racing heart, shallow breathing—and are familiar with the feeling of being overwhelmed it can bring. The stress response is part of the “fight or flight” mechanism that has helped our species thrive. However, the demands of modern life make this adaptive response problematic for our long-term well-being. 

This article covers the physiological underpinnings of stress, its impact on various bodily systems and useful strategies for navigating it. 

The Physiology of Stress 

Stress can be defined as a state of disharmony or altered homeostasis within an organism. In other words, we strive to live in a stable and balanced environment, but stressful events alter homeostasis and upset the harmony of the body's systems. The body’s stress response is governed by the sympathetic nervous system. When faced with acute danger, your body responds with a cascade of physical and hormonal changes that prepare you to respond. Some of these changes include: 

  • Increased blood pressure and heart rate 

  • A surge of stress hormones (epinephrine, norepinephrine and cortisol) 

  • Reduced blood flow to internal organs and increased blood flow to muscles 

  • Heightened muscle tension 

  • Inhibition of immunity, digestion and reproductive functions 

When confronting danger, these physiological responses play a protective role in promoting survival. Once activated, the stress response mobilizes the body’s available resources to meet the demands of a dangerous or stressful situation. Any bodily functions and processes not immediately necessary, such as growth, digestion and the maintenance of hormones responsible for reproduction, get downregulated. Unfortunately, when the perceived threat stems from constant daily pressures, these responses can impact your overall well-being. Eventually, the body’s stress response may wreak more havoc than the stressor itself, impacting numerous health outcomes. 

Chronic Stress and Body Weight 

For some people, chronic stress may be associated with higher body weight. A variety of factors underlie this relationship. While some of the hormones associated with the stress response inhibit hunger, others increase it. Cortisol typically spikes in the latter parts of the stress response and stays elevated during the recovery phase. This hormone increases hunger and motivation to eat as a means of replenishing calories that might have been lost while responding to a stressor. The body’s stress response stimulates the sensitivity of the reward system leading to cravings for hyperpalatable comfort foods, such as quick-digesting carbohydrates and those that are high in fat, and people may begin to eat for emotional reasons rather than nutritional ones. 

In addition, cortisol spurs an increase in fat storage, particularly around the midsection. The fat cells located in the abdomen, known as visceral fat, are particularly sensitive to cortisol and store more fat than other areas when exposed to it.

Chronic Stress and Digestive Function 

Digestion is rapidly inhibited during stress. Blood flow is diverted away from digestive organs, gastrointestinal enzymes responsible for breaking down food decrease, and peristalsis (the muscular contractions of the intestines that help move food along) is inhibited. When facing a critical threat, this is beneficial. Digestion is not immediately necessary and blood flow is redistributed to other working tissues, such as the muscles needed for fight or flight. When stress becomes chronic, however, this alters the flow of the digestive system and it no longer functions efficiently. Stress can also increase markers of gastrointestinal inflammation and is related to conditions such as irritable bowel syndrome, ulcers, Crohn’s disease and ulcerative colitis. 

Chronic Stress and Mental Health 

Chronic stress can negatively impact mood, and high levels of stress are related to increased rates of both depression and anxiety. Prolonged exposure to cortisol and other corticosteroids can increase feelings of anxiety and contribute to the development of depression. Elevated cortisol levels are often seen in individuals with major depression, and animals with high corticosteroid levels show symptoms of depression, such as poor sleep, locomotor changes, reduced appetite and low libido. Additionally, individuals exposed to early-life stress are more likely to experience clinically significant mental health outcomes in adulthood. 

Chronic Stress and Disease 

Inflammation is part of the immune response to illness or injury, where white blood cells, antibodies and cytokines defend compromised tissues. Like stress, this is beneficial in the short term. Chronic inflammation, however, promotes the development of most chronic diseases. Unchecked stress can incite or perpetuate systemic inflammation, and research reveals that stress is a common risk factor in 75 to 90% of modern diseases, including cardiovascular disease, diabetes, liver disease, Alzheimer’s disease and cancer. 

The Benefits of Stress 

While it may seem that stress is inherently negative, it can be beneficial. Stress can boost cognition, motivation, memory, creativity, vigilance and perseverance. Furthermore, the way we perceive a stressor has a significant impact on how it affects us. Simply viewing a stressor as a “challenge” rather than a “threat” yields better physical and psychological consequences. Stress mindsets (our attitudes and beliefs about the effects of stress) alter our behavioral and psychological responses to threats, and thus, our long-term outcomes. For example, a study examining the association of perceived stress and depression in college students found that the higher the level of stress perception the more likely the person is to experience depression. 

To objectively test the effect of mindset on the physiological stress response, researchers set up an experiment involving a mock interview and measured two stress hormones: cortisol and dehydroepiandrosterone (DHEA). As mentioned earlier, cortisol is behind some of the deleterious effects of chronic stress. It helps break down stored fuel and inhibit unnecessary systems during the stress response, but chronically high levels can hamper health. DHEA also rises during a stress response, and promotes brain growth and recovery and affects emotions, immune reactions, mood and behavior because it easily crosses the brain-blood barrier. Researchers randomly assigned participants to watch either a “stress is enhancing” or “stress is debilitating” video before their mock interviews. They found that, compared to the “stress is debilitating” group, those who watched the “stress is enhancing” video had a dramatically greater rise in DHEA, which is linked to improved health outcomes in response to stress. 

Stress is a natural part of life. When unchecked, the body’s physiological response can negatively impact health. However, your mindset can transform your stress response, allowing it to enhance creativity, motivation and perseverance, ultimately helping you become more resilient in the face of future stressors.

If you are interested in learning more about how nutrition, physical activity, sleep, breathing and social connections impact mental health, check out this continuing education course from ACE: A Holistic Approach to Mental Health (worth 0.5 ACE CECs).