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The Affect of Stress on Food Intake
In today’s society, stress is common among individuals of every age, gender and ethnicity. Every aspect of life seems to contain stressful moments; whether in work, school, family or social settings, stress affects everyone at some point in their life. The extent to which stress hinders or aids in an individual’s ability to function depends on his reaction to and ability to handle the stressful situation. Everyone has their own coping strategies to handle stress, and some strategies are healthier than others. While some people are able to deal with stress without changing their normal behavior, it is rare that stress does not have some adverse affects on an individual. Often times, those affects reach the realm of eating behaviors. The investigation into whether stress leads to overconsumption or reduced food intake is widespread among different groups of humans and animals. Not only is the amount of intake examined, but also whether stress can invoke changes in the chosen types of food to eat. While there are clear biological changes that occur under stress, there are also emotional factors that can influence eating habits during stressful situations. Whether the individual is a restrained or emotional eater can change the way food is used to cope with stress. With the increasing problem of obesity and the increased levels of stress born by individuals, the correlation between stress and eating behaviors may help in counteracting the obesity epidemic.
According to Torres and Nowson, stress can be defined as “the generalized, non-specific response of the body to any factor that overwhelms, or threatens to overwhelm the body’s compensatory abilities to maintain homeostasis.” Stress can mean different things to different people because not only are there different types of stress, but also each individual has different ideas of what constitutes a stressful situation. For example, some people become extremely stressed about public speaking or flying in an airplane while others may not elicit a stress response to these events. According to Miller and Smith, there are several different forms of stress, including acute stress, episodic acute stress, and chronic stress. Acute stress is the most common form and comes from demands and pressures of the recent past or of the near future. Acute stress is short-term and considered adaptive because it is thrilling and arousing in situations that require additional energy. However, frequent acute stress, or episodic acute stress, can have damaging effects on one’s body. People with episodic acute stress describe themselves as having a lot of nervous energy and often experience irritability, anxiety, tension and over arousal. These conditions can lead to persistent headaches, hypertension, and heart disease. Chronic stress is the long-lasting stress that wears on the body and comes when people never see a way out of a miserable situation. It’s the stress of never-ending demands and pressures and can lead to physical and mental breakdown. While acute stress is usually not harmful and often experienced, chronic stress weighs down on people and can lead to health problems. (http://www.apahelpcenter.org/articles/article.php?id=21)
While stress in today’s society holds a negative connotation, there are both positive and negative stressors that can lead to the stress response. According to Mills, Reiss, and Dombeck, there is a distinction between eustress, or positive stress, and distress, or negative stress. Eustress can be motivating, focusing, energizing, and can improve performance. Distress, on the other hand, can cause anxiety, concern, decreased performance and ultimately mental and physical problems. It is difficult to identify positive and negative stressors because each individual will react to stressful situations differently. However, some examples of positive stressors may include starting a new job, marriage, moving, and taking a vacation. Some examples of common negative stressors may include death of a loved one, injury, illness, a conflict in a relationship, unemployment and legal problems. Along with positive and negative stressors, there are also different physical, chemical, physiological and social stressors that can induce the stress response. Since there are different stressors as well as different kinds of stress, it can be difficult to study the effects of any one type of stress on food intake. Individuals vary not only in how they perceive stress and stressors but how they react to situations. (http://scf.mhmrtc.org/poc/view_doc.php?type=doc&id=15644)
There have been many studies done on rats to examine the stress response and its relation to food intake. Rats make easier test subjects then humans because there are few confounding variables involved and stress can be invoked rather easily. In a study done by Marti and Armario, the effects of exposure to chronic stressors of different intensities and daily duration on food intake were examined in adult male rats. There were three different stressors used, handling, restraint, and immobilization, as well as three different daily durations of 15, 60 and 240 minutes. The rats were randomly assigned to the experimental groups with the inclusion of a control group that received no stressors. Food intake was measured by how much food was gone from the feeders each day and the experimenters also monitored the rats’ body weight. The study concluded that chronic exposure of a certain severity induces anorexia and reduces overall body weight of the rats. The handling (low stress) had little effect on food and weight, while restraint (medium stress) slightly reduced food intake and weight, and the immobilization (high stress) caused more severe reductions in food intake and weight. Therefore, the more intense the stressor and the longer the duration, the greater reduction in food intake and body weight in the rats. An interesting finding with the study was that the response of food intake to a given stressor showed few signs of habituation throughout the length of the experiment. This means that the rats did not adapt to the stressors and continued to show a stress response each time the stressor was enacted. (Science Direct)
In another study done by Kurlyama and Shibasaki, rats were used to examine the sexual differentiation of the effects of emotional stress on food intake. Male and female rats underwent a 1-hour period of one of three different stressors, either restraint, electrical shock, or emotional stress induced by a communication box. While all three stressors inhibited food intake in both genders, only the emotional stress caused a gender difference in the amount of reduction. Female rats had a 48% reduction in food intake following the emotional stress, while males only had a 22% reduction. This study shows that females may exhibit a larger response to emotional stress than males and that females reduce their food intake the most with emotional stress. (http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20043079753)
The studies done on rats conclude that stress invokes a reduction in food intake in the animal; however, this same conclusion is not seen in studies done on humans. While it is relatively easy to design a proper study with rats and invoke stress, there are limitations on the studies done on humans and other variables involved in measuring stress and food intake.
While the studies on rats are relatively simple and easy to orchestrate in a laboratory, studies on humans are more difficult to conduct. Since there are so many different stressors and reactions to stress it is hard to recreate stress within a lab and monitor the direct effects from a stressor. However, there have been studies done to try to examine the effects of stress on food intake in humans. In one study done by Wardle, Steptoe, Oliver and Lipsey, the association between work related stress and nutritional status in relation to dietary restraint was examined in adults. The design of the study included both a cross-sectional and a longitudinal element. The study used 90 staff members of a large department store with 58 women and 32 men. Over a 6-month period, these staff members were assessed on four occasions with measures of diet, weight, and perceived stress. To determine the level of work stress, the number of hours was recorded over a seven-day period to provide an objective indicator of stress. Participants worked an average of 47 hours on the high stress weeks and 32 hours on the low stress weeks. The high stress weeks were compared with the low stress weeks in terms of gender and restrained eating. The study found that high stress work periods were associated with higher energy, saturated fat and sugar intake. An interesting finding was that those participants who were identified as restrained eaters (those on a diet) tended to respond to work stress with a greater appetite and consumption of food then those who were not identified as restrained eaters. Restrained eaters in this study were more vulnerable to an increase in food intake due to the effects of work related stress. This study focused solely on stress created by working long hours on the job, and cannot be broadened to the numerous other types of stress. (http://grande.nal.usda.gov/ibids/index.php?mode2=detail&origin=ibids_references&therow=378217)
In a review of studies done by Torres and Nowson, the relationship between stress and eating behavior was examined as well as the link between stress and weight gain. The review looked at numerous studies that involved both acute and chronic stress on humans to determine whether there is a direct correlation between stress and food intake. The studies they looked at found conflicting results, as both decreased and increased eating was found as a response to stress. A retrospective survey of U.S. Marine’s food intake during combat provided an example of the response to a severely stressful situation. The results showed that during the first day of combat 68% of marines reported eating less than usual, with the main reason for decreased food intake being fear. In another study on 212 students, the subjects self-reported their food intake and stress levels. The study found that 42% of students reported eating more in response to stress while 38% reported eating less. The effect of a major stressful event such as a school examination on food consumption was investigated in 225 male and female high school students. Total energy intake was significantly greater on the examination day when compared to stress-free days. These conflicting results are inconclusive as to whether stress increases or decreases food intake; however, the results may be due to limitations on studies and external factors that were not controlled in the experiments.
Torres and Nowson also looked at the effects of stress on the types of foods consumed. In a large cross-sectional study, 12,110 individuals were investigated on stress and food intake. The study’s results showed that greater perceived stress was positively associated with a higher-fat diet. Laboratory studies show mixed results due to the limitations on inducing stress in humans within a laboratory and the ability to measure dietary intake. Most laboratory experiments are only able to induce acute stress on individuals. However, there is evidence from longitudinal studies that chronic life stress is associated with a high-fat diet and a greater preference for sweet foods. Evidence was also found through cross-sectional studies that stress is positively associated with weight gain due to the higher food intake. (Science Direct)
The effects of stress on food choice were examined in a laboratory study done by Oliver, Wardle and Gibson. The study involved 68 healthy men and women divided into two groups. One group was exposed to a stressor that involved having to prepare a four-minute speech to be given after lunch. The second group was the control group that was not exposed to a stressor. Both groups were given lunch, and the food choices of the two groups were examined. The results showed that the stress did not alter level of food intake during the lunch meal; however, identified stressed emotional eaters ate more sweet high-fat foods and a more energy dense meal than unstressed and unemotional eaters. (http://www.psychosomaticmedicine.org/cgi/content/abstract/62/6/853)
Another study, by Oliver and Wardle, also looked at the effects of perceived stress on food choice. In a questionnaire given to 212 students, the subjects reported effects of stress on eating behavior and food. In 73% of the respondents, snacking behavior was increased during times of stress. The intake of “snack-type” foods increased during stressful periods while the intake of “meal-type” (fruits, vegetables, meat and fish) foods actually decreased in response to stress. (http://www.ncbi.nlm.nih.gov/pubmed/10357442) In a similar study, done by Cartwright, Wardle, Steggles, Simon, Croker, and Jarvis, stress and dietary practices were examined in adolescents. The study used a group of 4,320 schoolchildren with a mean age of 11.83 years and included both males and females. The subjects completed a questionnaire regarding measures of stress and four aspects of dietary practice. The four aspects were fatty food intake, fruit and vegetable intake, snacking and breakfast consumption. The students used were from diverse socioeconomic and ethnic backgrounds. Analysis of the survey results showed that greater stress was associated with more fatty food intake, less fruit and vegetable intake, more snacking, and a reduced likelihood of daily breakfast consumption. These results show that stress may lead adolescents towards unhealthy eating behaviors that will have long-term effects on their health. While amount of overall food intake was not measured, it is clear that there was a significant change in food choices under stressful situations. (http://cat.inist.fr/?aModele=afficheN&cpsidt=15062857)
Since there have been studies that reveal both increased and decreased food intake, some researchers have looked at the body’s physiological response to stress to understand what causes this difference. The stress response involves the release of cortisol from the adrenal glands, causing a widespread physiological response that prepares the body to handle the stressful situation. A study, done by Epel, Lapidus, McEwen, and Brownell, looked at whether the cortisol reactivity level in women in response to stress leads to higher food intake. The study exposed fifty-nine healthy women aged 30-45 years old to both a stress session and a control session on different days. The stress session included 45 minutes of challenging tasks made stressful by giving unrealistic time constraints to meet the expected goals. After the stressors, participants were given a basket of snacks that included two higher fat sweet and salty snacks and two low-fat sweet and salty snacks. Cortisol reactivity levels were examined by measuring levels of salivary cortisol at the same time intervals throughout both the stress and control sessions. The results showed that women who were high cortisol reactors to stress ate more food than low reactors. The high reactors also tended to consume more sweet foods than low reactors across both stress and control days. However, this study is limited by laboratory settings and the stress inflicted was mostly acute stress and may not be applied to chronic stress or stressful situations outside of the laboratory.
The research done on humans in regards to the correlation between stress and food intake shows mixed results on whether stress causes an increase or a decrease in consumption. There are significant restraints in the laboratory setting to measure and test stress responses because of the numerous different kinds of stress and the fact that people react differently. The surveys and longitudinal studies reveal that there are people who react by increasing food intake and others who react by decreasing their food intake. Therefore, it is difficult to generalize any one conclusion about the change in total food consumption due to the infliction of stress. There are convincing results from studies that show that people change their consumption patterns in terms of food choice when they encounter a stressor. Individuals tend to choose more high-fat foods when dealing with stress and these high-fat foods often replace healthier foods such as fruits and vegetables. This shows that stress may lead to unhealthy consumption habits that could potentially inflict health problems on highly stressed individuals. While it is clear that animals, or at least rats, reduce their food intake in response to stress and can even become anorexic from severe stress, these results cannot be generalized to humans. The stress response is complex and some individuals react with higher cortisol levels than others, which may be a confounding factor in the changes in food intake.
There are many different coping strategies to deal with problematic situations, including stress. Some individuals are emotional eaters who respond to any uncomfortable experience by eating. These individuals will show an increase in food intake when dealing with stress; however, it is not a very healthy coping strategy. Using food to reduce anxiety can lead to unwanted weight gain. According to Women’s Fitness, the top ten ways of dealing with stress include measures such as talking about it, exercising, thinking positively, accepting one’s strengths and weaknesses, and to plan and prioritize so as to not get overwhelmed. While there may be causal links between stress and increased appetite and food intake, the studies have yet to provide conclusive results and individuals should focus on managing stress through healthy coping strategies. (http://www.womenfitness.net/top10_dealing_with_stress.htm)
Cartwright, M., Wardle, J., Steggles, N., Simon, A. E., Croker, H., & Jarvis, M. J. (2003). Stress and dietary practices in adolescents. Retrieved April 29, 2009, from American Psychological Association Web site: http://cat.inist.fr/?aModele=afficheN&cpsidt=15062857
Kuriyama, H., & Shibasaki, T. (n.d.). Sexual differentiation of the effects of emotional stress on food intake in rats. Retrieved April, 2009, from CAB Abstracts Web site: http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20043079753
Marti, O., Marti, J., & Armario, A. (2003, March). Effects of chronic stress on food intake in rats: influence of stressor intensity and duration of daily exposure. Retrieved April, 2009, from ScienceDirect database (doi:10.1016/0031-9384(94)90055-8): http://www.sciencedirect.com/
Miller, L. H., Ph.D., & Smith, A. D., Ph.D. (n.d.). Stress: the different kinds of stress. In APA Help Center. Retrieved April, 2009, from American Psychological Association Web site: http://www.apahelpcenter.org/articles/article.php?id=21
Mills, H., Ph.D., Reiss, N., Ph.D., & Dombeck, M., Ph.D. (n.d.). Types of Stressors (eustress vs. distress). In Stress management. Retrieved April, 2009, from http://scf.mhmrtc.org/poc/view_doc.php?type=doc&id=15644
Oliver, G., & Wardle, J. (1999, May). Perceived effects of stress on food choice. Retrieved April, 2009, from PubMed database (PMID: 10357442): http://www.ncbi.nlm.nih.gov/pubmed/10357442
Oliver, G., PhD., Wardle, J., PhD., & Gibson, E. L., PhD. (2000). Stress and food choice: a laboratory study. Retrieved April, 2009, from Psychosomatic Medicine Web site: http://www.psychosomaticmedicine.org/cgi/content/abstract/62/6/853
Top 10 ways of dealing with stress. (n.d.). Retrieved April 29, 2009, from Women Fitness Web site: http://www.womenfitness.net/top10_dealing_with_stress.htm
Torres, S. J., & Nowson, C. A., Ph.D. (2007, September). Relationship between stress, eating behavior, and obesity. Retrieved April, 2009, from ScienceDirect database (Doi: 10.1016/j.nut.2007.08.008): http://www.sciencedirect.com
Wardle, J., Steptoe, A., Oliver, G., & Lipsey, Z. (2000, February). Stress, dietary restraint and food intake. Retrieved April, 2009, from IBIDS Web site: http://grande.nal.usda.gov/ibids/index.php?mode2=detail&origin=ibids_references&therow=378217
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