It is well established that both acute and chronic stress can be detrimental to health and well-being by directly increasing the risk of several chronic diseases and related health problems. Stress may contribute to ill-health indirectly via its downstream effects on individuals’ health-related behavior, such as promoting the intake of unhealthy palatable foods high in fat and sugar content.
There are misleading and confusing pieces of information out there relating to exercise and diet, some of them being all calories are equal in value, and others that exercise can undo our eating habits. Let’s break these down to determine if enough exercise, or exercise alone, would result in weight loss. These misunderstandings come from the public perception that obesity is solely an issue of inactivity and that all calories are the same.
Understanding Stress and Its Impact
Stress Models
Exposure to stressors and acute stress, is inevitable and it is common to experience stress as we strive to best use our resources to meet the requirements of our ever-demanding environment. Hans Selye, often referred to as the “father of stress”, defined stress as a nonspecific response of the body to any demand made upon it [17]. The stimulus that causes a stress response is termed a “stressor” [18] and these stressors may be classified as external or internal in nature. External stressors include stimuli such as major life changes (e.g., marriage, new home, death of a loved one), unpredictable events (e.g., car breakdown, unplanned pregnancy), or social demands (e.g., meeting new people). Internal stressors, on the other hand, refer to stimuli such as personal fears (e.g., public speaking, fear of flying), uncertainty (e.g., awaiting results of a medical test), or unrealistic perfectionistic expectations [19].
Acute stress is experienced when demands and pressures of the recent past and/or anticipated demands and pressures of the near future are present (i.e., recent and/or anticipated stressors), whereas chronic stress is associated with extended periods of unrelenting demands and pressures (i.e., long-term exposure to stressors) [19]. Individuals may respond to stressors differently depending on the type, nature and subjective interpretation of the stimuli and as a result, various stress models have been developed with the goal of better understanding the nature of the stress response.
In the GAS model, Selye [17] proposed that different types of stressors result in a similar physiological response. The GAS theory consists of three phases, the alarm stage, resistance stage and exhaustion stage. In the alarm stage, the body responds with a burst of energy to deal with the presence of a stressor (acute in nature), also known as the “fight or flight” response [21]. In addition to an increase in heart rate, breathing rate and blood glucose levels, the adrenal glands release cortisol and adrenaline (catecholamine). After this initial response to the stressor, the resistance stage involves the body remaining on guard and the adrenal cortex continuing to release glucocorticoids (cortisol) to help the body react to the stressor until the stress is resolved, or the body can no longer resist and reserves are depleted. Lastly, the exhaustion stage occurs when the stressor continues without resolution for a sufficient time period or at a sufficient intensity, such that energy reserves are depleted. Some suggest that high levels and/or prolonged stress during this stage may leave the body vulnerable to physical and mental illness or disease [22].
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Other researchers have focused more closely on the psychological aspects or nature of stress. Lazarus and Folkman [20] claim stress does not directly result from stressors; but rather, emerges because of an individual’s inability to satisfy the demands that accompany a stressor. Within their Transactional Model, these scholars emphasize that “stress” occurs as a result of an imbalance between what a situation demands and the resources an individual possesses in relation to those demands. The Transactional Model consists of a two-stage cognitive appraisal process (i.e., the primary appraisal and the secondary appraisal). In the stage of the primary appraisal, the individual identifies how personally significant and threatening the stressor is and determines whether the stressor is a “threat”, “challenge”, or “harm-loss”. More specifically, individuals appraise the stressor as a “threat” when the anticipation of harm is imminent, a “challenge” when a person anticipates opportunity gains, or a “harm-loss” when psychological damage has already been experienced. Also, specific types of emotional reactions are proposed to be associated with each different primary appraisal classification [23]. For instance, an appraisal of a stressor as a threat might stimulate the individual to feel worried, fearful, or anxious; a challenge appraisal might evoke confidence, eagerness and hopefulness; and, a harm-loss appraisal might elicit anger, disgust, disappointment, or sadness. In the secondary appraisal, which operates independently from but may happen contemporaneously with, the primary appraisal, individuals assess their coping resources and their ability to meet the demands of the stressor. As evidence of the inter-relationships between primary and secondary appraisals, it is recognized that in some situations, the secondary appraisal may actually become the cause of a primary appraisal.
Of note, most often in the literature, the term “stress” is not used to describe specific components of the transaction between the person and the environment [24] but rather to represent the overall process incorporating stressors, stress demands, appraisals and stress responses (physiological and psychological). Hence, in this review, unless referring to a specific component of the stress model, we use the term “stress” to represent the overall process.
Eustress vs. Distress
However, as discussed previously, exposure to stressors need not always be considered a “bad” thing. “Eustress”, for example, is a term introduced by Selye to represent “positive stress” and was later defined by Lazarus [26] as a positive stress response when a stressor is perceived as a challenge (i.e., primary appraisal of the Transactional Model). Indeed, in very early work, the concept of eustress was outlined within the Yerkes-Dodson curve [27]. The Yerkes-Dodson curve indicates that as stress levels increase, individuals’ performance in response to stress may also increase, to the point that an optimal level of stress is reached. Up to the point of optimal stress, individuals are proposed to adopt challenge appraisals and perceive that they have the resources to cope with the stressors. There is empirical support for this notion where some level of stress can drive perseverance in situations such as meeting work deadlines or striving to perform at one’s best in sport [28,29].
There are instances, however, in which exposure to stressors stimulates a negative stress response. In these situations, “distress” reflects a negative stress response, where the stressor is appraised as a threat or a harm-loss. According to the Yerkes-Dodson curve [27], performance levels may decline when levels of stress exceed the optimal point on the curve. Beyond this optimal level of stress, stressors are likely to be perceived as overwhelming or excessive and individuals may appraise these stimuli in a more negative light, resulting in them questioning whether they have the necessary resources to cope effectively. Poorly managed, overwhelming stress can result in exhaustion (i.e., last stage of the GAS model), psychological breakdown (e.g., depression, anxiety, insomnia) and other detrimental health consequences (e.g., high blood pressure, weakened immune system and diseases that adversely affect the cardiovascular, neuroendocrine and central nervous systems) [32,33,34,35,36]. The significance of these implications is underscored by the prevalence of stress among the population; as many as 35 percent of Australians have reported significant levels of stress in their lives at a single time point [37]. More alarmingly, about 75% of adults reported moderate to high levels of stress-most likely in the form of distress-in the 2014 Stress in America survey [38]. Besides affecting many adults, stress is also a pervasive health concern for teenagers and stress among adolescents may contribute to serious long-term health implications if not adequately addressed [39].
Stress-Induced Eating
Stress can directly increase the risk of chronic diseases and health problems but can also indirectly influence these outcomes via its effects on health-related behaviour [40,41]. For instance, sleep habits, substance use (including alcohol and smoking) and food choices are behaviours often negatively affected by stress [42]. For instance, stress is considered one of the major contributors to the initiation and continuation of alcohol and drug use as well as addiction relapse [43,44]. Cole and colleagues [45] found that life stressors and perceived levels of stress were positively correlated with alcohol drinking behaviour. Despite the significant and detrimental impact of stress on alcohol consumption and drug use, the primary focus of this present paper is on the influence of stress on food intake and food choices.
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With reference to the relationship between stress and food intake, 30% of respondents in the 2013 Stress in America survey reported skipping a meal when stressed, with 41% of the people who skipped meals reporting that they did so at least on a weekly basis [39]. Interestingly, the results of the same survey showed that 38% of adults reported overeating or increasing the consumption of unhealthy food because of stress; and approximately half of these adults (49%) reported engaging in these behaviours once or more each week [39]. As reflected in the above statistics, there appears to be individual variation in terms of the exact nature of the relationship between stress and food intake. Some investigators have reported that individuals report or display higher caloric intake during stressful periods [46,47,48,49], others have failed to find any overall difference in energy intake between stressful and non-stressful situations [50,51,52] and some have reported decreases in appetite and food intake when exposed to an acute stressor [53]. The reasons for this are likely multi-factorial and with factors such as gender, body mass index, restraint in eating [54] and even the time of the day [55] potentially moderating stress-induced eating.
Despite the discrepancies reported in previous studies regarding the overall amount of energy intake in response to stress, researchers typically report a shift in food choices-in both humans and animals-toward foods high in fat and sugar content under stressful conditions. In animal studies, it has been observed that animals increase food intake when in a mildly or moderately stressful environment and when provided with access to highly palatable food that is high in fat and sugar [56,57,58]. This observation is consistent with human studies examining food choice in response to stress [59,60,61,62]. Indeed, when provided with choice, foods consumed during times of both chronic and acute stress typically favor those that are energy-dense, with increased fat and/or sugar content [63,64,65]. This shift in food choice, toward the consumption of more pleasurable or palatable foods in stressful situations, appears to occur regardless of alterations in the total caloric intake [6,66,67,68,69,70]. This phenomenon is also observed under controlled laboratory circumstances, with an increase in the intake of “comfort” foods when both humans and animals are placed under acute physical or emotional stressors [64,65,70,71,72,73,74], even when individuals have high satiety and have no homeostatic need for calories [64,75]. The precise mechanisms through which stress influences food intake are likely multi-faceted and may be both physiological and psychological in nature.
The Myth of "Out-Exercising" a Poor Diet
The idea that one can simply "out-exercise" a bad diet is a common misconception. While exercise is undoubtedly beneficial for overall health, relying solely on physical activity to compensate for poor dietary choices is not an effective or sustainable strategy for weight management or disease prevention. It can require an hour or more to burn through calories that take only minutes to consume.
Calories Are Not Created Equal
While 100 calories from fruits and vegetables and 100 calories of brownies are both 100 calories, they are not equal. The fruits and vegetables will include more vitamins and nutrients, and likely the volume of these foods will be a larger amount than the brownie, making you feel full for longer. Overeating, even of high-quality nutrient-dense foods, can still result in weight gain. When looking at making caloric restrictions, we’ll want to plan to eat more nutrient-dense items, so that you feel more satisfied and get more nutrients while consuming fewer calories.
Focusing solely on calories is also a mistake, because not all calories are equal. Counting calories or carbs can be tedious and become all-consuming. But not all carbs are bad, just as not all calories are equal. For example, 50 calories of sugar is not the same as 50 calories of nuts if your body needs protein following a hard workout.
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Exercise and Diet: A Synergistic Relationship
Exercise and diet cannot replace each other, as they both serve different roles. While both positively impact health, they do so in different ways. The diet helps us to feel good and get the nutrients we need to maintain our proper body functions. Exercise goes beyond weight control. Taking part in regular physical activity helps in other areas like heart health, muscle mass, bone strength, diabetes management, improving mental health, and more. They work so much together, it really is a marriage that makes them both a part of the regular recommendations for heart health.
Physical Activity has many benefits beyond weight control, including strengthening muscles, bone density, diabetes management, and improving mental health. Physical activity improves several health indicators such as blood pressure, resting heart rate, waist circumference, visceral fat, insulin sensitivity, leptin sensitivity, blood lipid levels, physical fitness, body composition, and also psychological health indicators such as an improved mood [5,6]. In addition, due to physiological aging, muscle and strength loss (i.e., sarcopenia) occur due to a lack of physical stimuli.
The Importance of a Balanced Approach
Maintaining both diet and exercise is hard. It’s estimated over 2/3rds of Americans are in the overweight/obese category, and only about 50% of Americans meet physical activity recommendations of 150 min/week of moderate-intensity exercise (2). We’re very good at overestimating the calories expended during exercise, and underestimating the calories we consume. So, how do we aim for a balance of diet and exercise? That’s just it, it takes balance, self-care, and patience. Aim for both, and balance where you can. Workday consuming your time and energy? Try to get out for a short walk and get the movement where you can, but every day doesn’t need to be a hard workout. These same days, aim for making healthy diet choices. Set yourself up with some meal planning and healthy, accessible snacks so you’re not caught in a pinch. Do you have a fun celebration coming up, that good food is likely going to be a part of? Enjoy the good food and celebrations, and try to get your work out earlier in the day. Don’t aim for perfection, it’s not all or nothing. Working on your health is a life-long process, not a destination.
“To truly live a healthful lifestyle requires both diet and exercise,” said Deborah Rohm Young, Ph.D, director of behavior research at Kaiser Permanente Southern California.
The Role of Physical Activity in Regulating Eating Behaviors
Physical activity and diet are two predominant determinants of population health status that may influence each other. Physical activity has been identified as a behavior that may lead to a healthier diet and regulates eating behaviors.
Motivation and Eating Styles
Self-determination theory, proposed by Deci and Ryan [10], states that humans have a natural inclination to act in line with their motivational state in a given setting. This theoretical paradigm focuses on contextual circumstances and the causes and consequences of self-determined behavior. This framework distinguished self-determined motivation from non-self-determined motivation based on the quality of motivation rather than quantity [10]. Self-determined motivation assumes that the behavior is performed due to the positive values inherent in the behavior, while the person integrates the behavior into his/her daily lives, and includes identified regulation, integrated regulation, and intrinsic motivation, the three most self-determined forms of motivation present on the motivational continuum. This motivation is described as participating in a conduct that is viewed as being congruent with intrinsic goals or outcomes and stems from the individual’s identity, such as healthy eating. Individuals that engage in self-determined motivational actions have a sense of choice, interest, and satisfaction and, as a result, tend to persist in the healthy eating behavior. Non-self-determined motivation assumes that the performance of the behavior is adjacent to coercive or self-imposed assumptions and it includes introjected regulation, external regulation, and in some instances, amotivation, the three least self-determined forms found on the motivational continuum based on the assumptions of the self-determination theory. Individuals who participate in a controlled behavior feel a sense of obligation and pressure and tend to stick with the conduct only as long as the external or self-imposed contingency is present. The action is likely to be abandoned if the stimulus is removed. Individuals who operate on the basis of a regulated incentive are thus less likely to be self-determined in the long run [10].
In a recent study, physical activity was positively associated with a greater correspondence between food need and food intake; that is, a greater perceived control in following the sensation of hunger and satiety. These results confirm previous studies which suggested physical activity as an entry point to a healthier diet [11]. Approaches that intuitively and cognitively stimulate the homeostatic regulation of food intake through hunger and satiety signals have been explored and have gained recognition. Physical activity has been highlighted as behavior that leads to a healthier diet and is essential in regulating weight in various populations, including individuals of a normal weight. This behavior influences physiological processes such as appetite control and psychological aspects such as self-efficacy and body image, leading to greater self-determined motivation and, consequently, improvements in dietary self-regulation [3,11].
The Impact of Physical Activity Levels
Higher levels of physical activity may have greater effects on eating behavior motivation. Physical activity may lead to a higher rate of weight loss success, in part because of its effects on eating behavior, such as more flexible food constraints and a lower pattern of emotional eating [13]. On the other hand, a lower involvement in physical activity is associated with extrinsically motivated eating behavior and is associated with a higher body mass index (BMI) as described by Castro et al. Further studies are needed to explore the mechanisms involved in appetite control that account for differences between individuals, such as body composition, postprandial satiety, hunger signaling peptides, insulin and possibly leptin sensitivity, gastric emptying, and the basal metabolic rate [15]. The possible role of appetite-controlling peptides such as CCK, GLP-1, PYY, ghrelin, or recently discovered nesfatin-1 (see Prinz et al. [16]) could have its basis on physical active behaviors due to the implications of physiological changes due to exercise. The effect of exercises on the levels of appetite-related hormones and appetite have also been described [17], suggesting that physically active behaviors can lead to motivations that are in line with healthy habits since physiological changes occur at the same degree [18]. It is known that as people become more physically active, they move from an unregulated to a regulated zone of appetite control and better match their energy expenditure to their needs [1,6]. However, the levels of physical activity that can induce the greatest physiological and behavioral changes concerning motivation and eating behaviors remains understudied [14].
Practical Strategies for Balancing Diet and Exercise
Focus on Whole Foods: Strive to consume as many whole foods as you can. Whole foods are minimally processed - they include vegetables, whole grains, nuts, seeds, beans, lentils, milk, unprocessed meats and fish.
Prioritize Inclusions Over Exclusions: Focus on what to include in your diet - whole grains, fruits, nuts, seeds, vegetables, etc. - may be more important than focusing on what to avoid.
Practice Mindful Eating: Pay attention to your body's hunger and satiety cues. Eat when you're hungry and stop when you're full.
Plan Ahead: Meal planning and preparation can help you make healthier choices, especially when you're short on time or feeling stressed.
Find Activities You Enjoy: Choose physical activities that you find enjoyable, which will make it more likely that you'll stick with them long-term.
Seek Professional Guidance: Consider consulting a registered dietitian or certified personal trainer for personalized advice and support.