Unraveling the Stress- Eating-Obesity Knot
Exercise can significantly mitigate the effects of stress and weight gain.
Elevated stress is a risk factor for cancer, high blood pressure and cardiovascular disease (Block et al. 2009). How stress influences eating behaviors and leads to obesity is a key topic of interest to researchers and exercise professionals.
A substantial amount of scientific research has been committed to unraveling this complex question. Block et al. submit that some people may gain more weight under stressful circumstances, while others may lose it and still others may have little change in weight. This article will summarize the state of knowledge regarding how stress can lead to higher food consumption, fat accumulation in the midsection, weight gain and obesity.
Torres and Nowson (2007) define stress as the nonspecific response of the body to any stimulus that overcomes, or threatens to overcome, the body’s ability to maintain homeostasis (the equilibrium of internal biological mechanisms). The authors explain that the stress response may be caused by social stressors (e.g., life events, personal conflicts); physiological stressors (e.g., pain, vigorous exercise, intense heat or cold); psychological or emotional stressors (e.g., sorrow, fear, anxiety); and/or chemical stressors (e.g., blood acid-base imbalance, low oxygen supply).
If the stressor represents an “ongoing” hassle, fear or overwhelming issue in a person’s life, the effect is referred to as chronic stress. In contrast, if the stressor is more temporary and immediate, the effect is referred to as acute stress. The body perceives an acute stressor (e.g., dealing with a traffic jam) as a challenge that a human being is capable of handling. On the other hand, chronic stress can seem unmanageable. Physiologically, the human body responds differently to acute and chronic stress.
During periods of acute stress, the medullar part of the brain signals the release of several “stress hormones,” including epinephrine (another name for adrenaline) and norepinephrine (another name for noradrenaline) from the adrenal glands. These hormones trigger physiological “fight-or-flight” mechanisms, which include increases in heart rate, respiration rate, fat and carbohydrate breakdown, and blood pressure (see Figure 1). Simultaneously, the body slows down other physiological processes, such as blood flow to the digestive system, appetite and food intake. The body is priming itself with the immediate energy, reflexes and muscular strength it may need to act in response to the stressor. This is an automatic physiological response to a real or perceived risk that endangers a person’s present status. When the threat that triggered the response has been eliminated, the body and mind return to a state of calm.
With chronic stress, the hypothalamus (the central control station for stress) directs the pituitary gland (below the hypothalamus) in the brain to send a signaling message hormone (known as adrenocorticotrophic hormone, or ACTH) to the adrenal cortex (the outer portion of the adrenal glands on the kidneys). ACTH triggers the release of cortisol (see Figure 2) (Adam & Epel 2007). This reaction is referred to as the hypothalamic-pituitary-adrenocortical (HPA) axis, and it is most active in humans during the early-morning hours (Björntorp 2001).
If the chronic stress (real or perceived) is of sufficient magnitude and duration, the HPA does not wind down (as it should), resulting in prolonged elevation of cortisol levels. Thus, chronic stress leads to daily increases of cortisol secretion. Cortisol is known to stimulate appetite during the intermittent recovery periods that occur while a person is experiencing chronic stress. Cortisol (with the help of slightly elevated insulin levels) has also been shown to activate lipoprotein lipase, the enzyme that facilitates the deposition of fat (Björntorp 2001). In the presence of slightly higher insulin levels, elevated cortisol levels inhibit the breakdown of triglycerides, thus promoting fat storage. Epel et al. (2000) report that chronic stress consistently contributes to greater central fat accumulation in females.
Additionally, chronic stress is associated with emotional changes that can include increases in anxiety, apathy and depression (Torres & Nowson 2007). The response to chronic stress may lead to much higher consumption of food, referred to as stress-induced eating.
Stress-induced eating may be defined as making oneself feel better by eating or drinking in response to a stressful situation (Torres & Nowson 2007). Greeno and Wing (1994) proposed two models of stress-induced eating. The first model, referred to as the general-effects model, predicts that stress will induce some type of psychological change that results in eating. The second, more commonly accepted model is referred to as the individual-differences model. This model suggests that owing to background learning, personal attitudes and biological differences, some people will change their eating habits under stressful conditions while others will not (see Figure 3).
Dallman (2010) asserts that in response to chronic stress and personal strains (e.g., interpersonal relationship, financial or lifetime aggravations), 40% or more of people will increase their caloric expenditure; 40% will decrease their caloric intake; and 20% will not change their eating behavior in any way. Consequently, stress-induced eating may be directly associated with weight gain and obesity for some people, but not for others.
Torres and Nowson add that during periods of chronic stress, people often have limited time to prepare healthy food choices and consequently tend to choose fast foods, which are usually more calorically dense. According to Dallman, the research suggests that overweight individuals tend to eat more when exposed to chronic stress, whereas normal-weight or underweight individuals do not. It appears that people who are chronically stressed—regardless of whether they eat more or less—tend to choose more pleasurable or palatable foods containing higher levels of fat and/or sugar (Dallman 2010).
Dallman adds that eating highly palatable foods temporarily decreases stress levels, which reinforces more eating of pleasurable foods. Thus, dealing with life’s stressors using food can become an incessant cycle that continues to contribute to obesity. Interestingly, Garg, Wansink and Inman (2007) note that when individuals who are in a saddened (or stressed) state read nutrition labels before eating, they indulge less in “hedonic” (pleasurable) foods.
The most comprehensive recent review on the health benefits of exercise and physical activity comes from the Physical Activity Guidelines Advisory Committee Report, 2008 published that year by the U.S. Department of Health and Human Services. In this exhaustive report, the section on mental health (part G, section 8) concludes that physical activity can protect against feelings of distress, defend against symptoms of anxiety, guard against depressive symptoms and the development of major depressive disorder and enhance psychological well-being. The document asserts that since 1995, more than 30 studies—involving more than 175,000 people—have been conducted in areas related to stress.
Although the measures of stress were not uniform in all of these research studies, the findings show with universal consistency that exercise interventions decrease stress levels and increase feelings of well-being. Dunn and Jewell (2010) add that exercise bouts of 30 minutes (but not longer than 60 minutes) appear to have the best “stress-reducing” benefits. There does not appear to be a differential effect based on the type of exercise (e.g., running, swimming, cycling, elliptical training, etc.). As to exercise intensity, the Physical Activity Guidelines report indicates that moderate to vigorous physical activity (with regular participation) reduces stress better than low-intensity activity.
Astin et al. (2003) declare that the overall consensus of the pathophysiological and epidemiologic research suggests that acute and chronic stress contribute to the genesis of coronary artery disease. The authors add that an abundance of randomized, controlled studies since 1996 have shown that mind-body programs reduce the recurrence of myocardial infarctions (i.e., heart attacks) and other dangerous coronary events. After reviewing the literature on mind-body research, the authors concluded that integrating mind-body programs into traditional medical interventions should be considered a priority.
Stress sends biochemical “shock waves” throughout the body that are useful in the short term. However, chronic stress unleashes a flood of hormones that may become toxic as the stress persists. Exercise professionals need to educate their clients on the importance of exercise and mind-body practices in reducing the metabolic and physiological effects of stress and potentially lowering the risk of cardiovascular disease, hypertension and obesity. Science indicates that some of the best stress reduction strategies are exercise, relaxation activities, yoga and mind-body programs. In the long run, a decrease in stress can save the body from disease.
Source: Adapted from Torres & Nowson 2007.
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1. What is the physiological difference between visceral and subcutaneous body fat?
Visceral, or central, body fat, which occurs in the intra-abdominal area of the body, is very different from subcutaneous, or peripheral, body fat, which is just under the skin. Visceral body fat has much greater blood flow and more glucocorticoid receptors. The glucocorticoid receptors regulate the fat accumulation effects of cortisol and are four times more concentrated in visceral fat than in subcutaneous fat (Epel et al. 2000). Thus, chronic stress, which elevates cortisol levels, results in fat accumulation in the intra-abdominal area of the body (Epel et al. 2000).
2. How does work stress effect obesity?
In a 9-year study of U.S. men and women, Block et al. (2009) found that there was greater weight gain in both genders among subjects who were having difficulty paying bills; experiencing job-related stress; or suffering from general anxiety disorders or depression.
3. Does work stress result in elevated cortisol levels?
Björntorp (2001) reports that several studies have shown that continual stress and strain at work, specifically with high demands and/or monotonous tasks or responsibilities, result in elevated cortisol secretion.
4. Are there any noticeable physical differences between men and women who experience chronic stress?
With women, perceived constraints in daily life and strains within family relationships are associated with greater weight gain (Block et al. 2009). It appears that men are more likely to deal with chronic stress with other oral behaviors, such as alcohol consumption and smoking, as opposed to overeating (Greeno & Wing 1994). However, Block and colleagues state that a lack of decision-making authority may also be associated with weight gain in men.
5. Does listening to music help reduce stress?
Yes. Luskin et al. (1998) propose that music has the power to calm, soothe and inspire. It can directly affect physiological parameters such as heart rate and blood pressure and has been shown to be effective in treating anxiety, stress and depression.
6. What does restrained eating mean and how is it affected by stress?
When eating is restrained, the person is making an attempt to control food intake. Adam and Epel (2007) note that restrained eaters tend to eat more (compared with free eaters—who do not control what they eat) when they are under chronic stress. Restrained eaters do not just eat more overall when stressed; they specifically eat more sweet and fatty foods during the high-stress period (Wardle et al. 2000). According to Wardle and colleagues, a reason for this response is that individuals who habitually attempt to control their weight by regulating their food intake (restrained eaters) may eventually lose this control under stressful situations.
7. Does the severity of the stress affect a person’s eating behavior?
Yes. There is a greater probability of eating less as the severity of the stress increases (Torres & Nowson 2007). Nevertheless, more research is needed to reach conclusive findings in this area.
8. Is abdominal obesity related to hypertension and cardiovascular disease?Bergman et al. (2007) note that visceral fat leads to a hyperactive sympathetic nervous system, contributing to the release of free fatty acids into the bloodstream and elevated insulin levels, which are causal precursors for hypertension and cardiovascular disease.
9. What is the difference between hunger and appetite?
Hunger and appetite are related to an individual’s desire to eat food. Both directly trigger eating. Hunger is commonly described as the psychological and biological need for food. It is a condition that results from consuming less than the recommended daily intake of calories. Hunger sensations range from slight discomfort to real stomach pangs. Appetite is the instinctive physical desire or craving for food. Appetite motivates an individual to eat at a particular time and also what to eat. Furthermore, appetite has an emotional component, given that it is a learned response that is closely associated with memories of past food experiences.
10. Will the time of day when a person exercises affect energy intake?
There are some claims in the popular media that exercising in the morning may be more effective for achieving greater weight loss. Surprisingly, there is little randomized, controlled research addressing this meaningful question. However, in a well-designed study with males, O’Donoghue, Fournier and Guelfi (2010) found that daily energy intake was similar regardless of whether exercise was performed in the morning, afternoon or evening. The authors concluded that individuals should exercise at whatever time of day best fits their schedule.
Source: Adapted from Green & Wing 1994.
Source: Adapted from Torres & Nowson 2007; Björntorp 2001.
The following stress management suggestions are from an article by Melissa Stoppler, MD (2008), and can be found on www.medicinenet.com.
1. Exercise. Exercise provides a distraction from stressful situations, as well as an outlet for frustrations. In many ways it acts as a buffer to the overflow of hormones that accumulate from daily stress. A combination of cardiovascular exercise, resistance training and mind-body programs helps optimize health and well-being.
2. Meditation. Stoppler suggests that in a meditative state, deep centering occurs with a focusing on the core of our being; this allows for a quieting of the mind and emotions, which helps relax tension in the body. During meditation, the brain enters an area of functioning similar to sleep, but with added benefits that we cannot achieve in any other state; these benefits include the release of certain hormones that promote health.
3. Progressive Muscle Relaxation. Progressive muscle relaxation involves tightening and then relaxing of the muscles in the body (in succession). This technique is based on the idea that mental relaxation will be a natural outcome from the physical relaxation.
4. Time Management. One of the biggest causes of stress is poor time management. Good organization of time is central to effective stress control. By learning to prioritize tasks and avoid overcommitment, we avoid the stress of being overscheduled, with too many responsibilities at work and in the family. Stoppler recommends using a daily planner and calendar to prioritize tasks and stay focused on those at hand; identifying regular time-wasting activities and eliminating them; and banishing procrastination.
5. Support Systems. According to Stoppler, studies indicate that people with a positive and helpful social structure—consisting of friends, family, loved ones and pets—experience fewer stress-related symptoms. Strong support systems make it easier to manage stress more efficiently.
6. Healthy Food and Drink. Dehydration and hunger tend to provoke feelings of stress and anxiety. Drinking plenty of water throughout the day and eating a nutritious diet can reduce stress.
7. Posture Check. Poor standing and sitting posture lead to muscle tension, pain and increased stress. Stress management strategies include checking posture regularly at work and during daily activities; avoiding stooping, slumping and repetitive-strain activities/movements; and developing healthy sitting, standing and working environments.
8. Recharging. Recharging means setting aside some time each day for energizing the mind. Purposely planning relaxation breaks as special incentives can help us cope with the daily challenges that often lead to chronic stress.
9. Speaking Slowly. Speaking slowly can be helpful in stressful or overwhelming situations. When we speak slowly, we think more clearly and often respond much more reasonably to a stressful situation.
10. Visualization. Gratifying or relaxing images calm the mind and body. Visualizing a soothing setting (e.g., outdoors in a meadow, by the ocean, along a mountain stream) while breathing in a slow, controlled way brings about a state of calm and relaxation.
Also known as adrenaline. It is secreted by the adrenal medulla in response to stress and acts on all body tissues. When produced in the body, it participates in the fight-or-flight response of the sympathetic nervous system by stimulating several physiological processes.
Also identified as noradrenaline. A fight-or-flight hormone that directly increases heart rate, triggers the release of glucose from energy stores, and increases blood flow to skeletal muscle. Norepinephrine serves a role in the suppression of appetite during acute stress.
A hormone that has an important effect on regulation of body weight, metabolism and reproductive function. Leptin serves an important role in long-term regulation of body weight, which is controlled by the hypothalamus in the brain.
A hormone involved in the regulation of energy balance and feeding behavior, including food intake and preference. Neuropeptide-Y increases the proportion of energy stored as fat and thus may contribute to the development of obesity.
Corticotropin-Releasing Hormone and Adrenocorticotrophic Hormone (CRH)
Secreted by the hypothalamus in response to stress. CRH is then transferred to the anterior lobe of the pituitary, where it stimulates the secretion of adrenocorticotrophic hormone (ACTH) and other biologically active substances. ACTH’s principal effects are increased production and release of cortisol from the adrenal cortex (outer layer of adrenal glands, which sit on top of the kidneys).
A steroid hormone secreted by the adrenal gland in response to stress. Cortisol increases blood sugar levels (when low and during endurance exercise) through a process called gluconeogenesis (formation of new glucose) that occurs in the liver. It suppresses the immune system and aids in fat, protein and carbohydrate metabolism. The amount of cortisol hormone present in the blood undergoes daily cyclic variation, with the highest levels present in the early morning (approximately 8:00 am), and the lowest levels present around midnight to 4:00 am, or 3–5 hours after the onset of sleep. Higher levels of cortisol are a contributing factor to the storage of body fat, particularly visceral, or intra-abdominal fat.
Astin, J.A., et al. 2003. Mind-body medicine: State of the science, implications for practice. Journal of the American Board of Family Practice, 16 (2), 131–47.
Bergman, R.N., et al. 2007. Abdominal obesity: Role in pathophysiology of metabolic disease and cardiovascular risk. American Journal of Medicine, 120 (2, Suppl. 1), S3–S8.
Björntorp, P. 2001. Do stress reactions cause abdominal obesity and comorbidities? Obesity Reviews, 2 (2), 73–86.
Block, J.P., et al. 2009. Psychosocial stress and change in weight among US adults. American Journal of Epidemiology, 170 (2), 181–92.
Dallman, M.F. 2010. Stress-induced obesity and the emotional nervous system. Trends in Endocrinology & Metabolism, 21 (3), 159–65.
Dunn, A.L., & Jewell, J.S. 2010. The effect of exercise on mental health. Current Sports Medicine Reports, 9 (4), 202–207.
Epel, E.S., et al. 2000. Stress and body shape: Stress-induced cortisol secretion is consistently greater among women with central fat. Psychosomatic Medicine, 62, 623–32.
Garg, N., Wansink, B., & Inman, J.J. 2007. The influence of incidental affect on consumers’ food intake. Journal of Marketing, 71, 194–206.
Greeno, C.G., & Wing, R.R. 1994. Stress-induced eating. Psychological Bulletin, 115 (3), 444–64.
Luskin, F.M., et al. 1998. A review of mind-body therapies in the treatment of cardiovascular disease. Part 1: Implications for the elderly. Alternative Therapies, 4 (3), 46–61.
O’Donoghue, K.J.M., Fournier, P.A., & Guelfi, K.J. 2010. Lack of effect of exercise time of day on acute energy intake in healthy men. International Journal of Sport
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Stoppler, M.C. 2008. Stress management techniques. MedicineNet.com. www.medicinenet.com/stress_management_techniques/article.htm; retrieved Oct. 29, 2010.
Torres, S.J., & Nowson, C.A. 2007. Relationship between stress, eating behavior, and obesity. Nutrition, 23, 887–94.
U.S. Department of Health and Human Services. 2008. Part G, section 8: Mental health. Physical Activity Guidelines Advisory Committee report. Washington, DC. http://www.health.gov/PAguidelines/Report/G8_mentalhealth.aspx.
Wardle, J., et al. 2000. Stress, dietary restraint and food intake. Journal of Psychosomatic Research, 48 (2), 195-202.
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