Can Stress Make You Overweight? Understanding The Science
Part 1 of 2
Given the social and physical drawbacks of being overweight, it is hard to not question the role of stress and food consumption comparable to that of a state of addiction as a causative factor in our current problems with obesity. Contrary to what many in great shape would believe, a large scale study found that 46% of participants would give up a year of their life in exchange for not being obese. 15% would give up 10 years of their life, 30% would rather be divorced and 25% would rather not be able to have children.[1] Needless to say, being overweight is hardly a goal and a significant number of people speak of a very real sense of powerlessness when it comes to overeating. A powerlessness that many of us can relate to at some point in life, especially during times of extreme stress. Obesity is best perceived as a multi-headed snake- a hydra of sorts with many causative factors as opposed to a phenomenon caused by one particular behavior or set of circumstances. The causes of obesity are indeed legion, but stress induced eating that manifests itself as a compulsion to continually consume more calories than are needed, in spite of conscious and determined attempts to eat less is most certainly a factor. Unfortunately, stress is only a part of the equation, as we will see that modern high fat and high sugar foods and their easy accessibility play a very tangible role in creating a cycle of compulsive eating comparable to an addiction. [2] In this two part article we will take a hard look at the science and mechanisms behind stress induced eating and show that for some members of the general population the problem isn’t just stress- it’s the type of stress in combination with the food environment that we live in. Thanks as always for reading and I do encourage you to share this article with those who you think would benefit from reading it.
While often cited as a major factor in the current global obesity epidemic, the impact of stress on our eating habits is not as clear cut as it is often presented in the media. Most of what we hear revolves around an overly simplistic model that simply says that modern life is stressful and stress makes you eat more- which explains the growing number of overweight citizens around the world. A compelling statement but incomplete in many ways as it does not paint the whole picture. Which is one of the main issues with oversimplified sound bites- as they leave us without a full or clear understanding of the problem and you can’t find a solution if the problem isn’t fully identified. One of the first things we should consider is that stress is not a modern phenomenon or one unique to living in a developed country. In fact life was far more stressful on going back only a few hundred years when for millenia, most humans on the planet faced each day with the uncertainty of finding food and survival as a whole. Historically and in impoverished countries today where life and death are constant struggles, human beings do not overeat and become overweight as a result of the extreme stress imposed upon them. On the contrary, animals usually eat less under periods of extreme stress- not more. [3,4] So much so that decreased food intake is seen as one of the most reliable ways to determine the severity of the stress an animal is facing- so there must be other factors responsible. What numerous studies reveal, however is that animals will INCREASE their food intake when under constant stress if given access to high sugar or high fat foods.[5,6]
Understanding the role that the combination of stress and highly palatable foods play in creating an environment conducive to overeating can go a long way in helping us understand how to deal with our growing problem with obesity.
It is quite a bit of a paradox that more stress equates to eating more food, but in human studies the research shows that stress affects certain groups of individuals differently. A small group of about 30% decreases their food intake when faced with high stress situations or after surviving difficult circumstances. On the other hand, the other 70% increases food intake while under stress.[7,8] Given that we live in a world where high sugar and high fat foods are both abundant and accessible, it makes sense that the most people would eat more under stressful conditions- which would be a significant contributing factor to our problems with obesity.[11] Almost half of the respondents to an American survey reported coping by eating and or smoking as a way of dealing with the stress in their lives.[9] Another found increased food intake during periods of stress to be much higher in women.[10] Clearly it isn’t a matter of us being more stressed now than any other time in history and we will take a look at how stress and what scientist term as highly palatable foods make us eat more than we should.
Understanding Stress & The Role It Plays With Our Eating Patterns
Under life threatening or ‘challenge’ type stress- the desire to eat is actually suppressed.
The first step is to identify what stress truly is as it is a term commonly used but not often understood. Stress is by definition a trigger that prompts our body to change and adapt in order to maintain some degree of equilibrium in an ever changing environment. This state of equilibrium, called homeostasis, is often short lived, as the stress of daily life requires constant adjustment on our part to be able to effectively deal with the world around us by initializing a cascade of time sensitive physiological and psychological changes that allow our bodies to adapt. Stress is not inherently a bad thing and you can thank the stress response for everything from bigger and stronger muscles, to greater endurance and a well sculpted body. (Read my article: How Muscles Get Bigger & Stronger). An important aspect of the stress response and the one that first comes to mind for most people is what is often termed the ‘flight or fight response’. We are very much a product of our evolutionary environment- which was for the most part a place of constant danger and uncertainty. When our ancestors were confronted by the threat of being devoured by a big cat or being bludgeoned to death in a territorial dispute with Lothar and the hill people, their bodies responded with behavioral, automatic and endocrinological responses that increased vigilance, increased heart rate and blood pressure while redirecting blood flow to the brain and muscles for immediate action.[11] It’s an important protective measure and one that stays with us today as we react the same way that most animals do when facing imminent danger. Under such conditions, your body diverts energy from unnecessary ‘housekeeping’ type activities like digestion and reproduction and instead uses all of its resources to focus on helping you stay alive.[12] Appetite, therefore is immediately suppressed which leads the significant decreases in food intake among individuals under stress when modern foods aren’t in the picture.[2,3] This applies today when facing an armed assailant in a dark alley just as much as it did when big cats and Lothar’s tribe were our main concerns. It’s relatively easy to envision as most of us can imagine that while standing in a dark alley at gunpoint, having a slice of chocolate cake is just about the last thing on your mind.
Understanding The Mechanisms Of Stress & How They Affect Our Eating Habits
At first glance, overeating due to stress would seem to be a bit of a paradox, and understanding how stress can make us eat more requires a deep look into the two main processes in our bodies that make up the stress response- the sympathetic adrenomedullary system and the hypothalamic–pituitary–adrenal axis.[13] The sympathetic andrenomedullary system (SAM) is activated rapidly under certain stressful conditions such as exercise or imminent danger and releases adrenaline and noradrenaline. Which increases heart rate, blood pressure, blood flow to muscles, increases metabolism and most importantly for our current focus, constricts blood flow to the gastrointestinal tract- stopping digestion and reducing appetite. This is in essence what happens during the fight or fight response- but there is another mechanism at work when we are under stress that isn’t as well known and this is the hypothalamic–pituitary-adrenal (HPA) axis.
Why Stress Triggers Overeating- Understanding The HPA Axis
Diagram of HPA axis- courtesy BrianMSweis
The hypothalamic-pituitary-adrenal axis is a complex set of interactions among the hypothalamus, the pituitary and adrenal glands that control critical adaptive measures to the stress response.[15] When you face a stressful situation, the hypothalamus (in your brain) reacts by secreting a hormone called CRH, (corticotropin-releasing hormone for those of you who like the big names) and vasopressin. CRH and vasopressin stimulate the pituitary gland to secrete ACTH (andrenocorticotropic hormone) which in turn acts on the adrenal glands to produce a class of glucocorticoids- one of which is the stress hormone cortisol. It’s important to note that all forms of stress are not the same and our body responds to different kinds of stress with different responses. Research has shown that stressors that we perceive as either an immediate danger or a challenging situation that we have the resources to cope with will stimulate a response by the SAM system. On the other hand, when faced with demanding situations that we believe we cannot cope with, or in circumstances where we face public embarrassment or a sense of failure the HPA axis is activated. This is significant since cortisol release is one of the main outcomes of HPA axis activation. Most of us are familiar with the role of cortisol as a stress hormone, but what isn’t common knowledge is that it can stimulate hunger and appetite.[2] Consequently stress that impacts us on a more emotional level are responsible for stress related eating behaviors.
Understanding The Role Of Cortisol’s Role In Stress Eating
Emotional stress triggers cortisol release and those who have high cortisol reactions to stressful situations eat more under stress than those who do not.
Under normal circumstances when the HPA axis stimulates cortisol secretion, there is what is referred to as a negative feedback loop which shuts down further cortisol production. When cortisol is released under stressful conditions, it feeds back to the brain which in turn triggers a signal to shut off further cortisol secretion.[16] This negative feedback loop is designed to keep levels within a stable operating range and to ensure that we are not exposed to prolonged periods of high cortisol levels- which, as we will see, can have rather negative effects.[16] Elevated levels of cortisol can increase how much you eat, as evidenced in the increased calorie intake in studies of individuals taking prednisone (a corticosteroid) for medical conditions.[17] Several studies have shown that individuals with severe eating pathologies, such as anorexia, bulimia and binge eating disorders have either greater basal cortisol levels and or a larger cortisol reaction to stressful situations.[18,19] In a study comprised of medical students, those who identified themselves as eating more under stress had far higher urinary cortisol and insulin levels during the high stress periods of medical exams when compared to those who did not identify as stress eaters. Their cortisol levels were also much higher during exams when compared to periods of relatively low stress during the summer vacation breaks and not surprisingly, those self-identified stress eaters with higher cortisol levels gained more weight than the control subjects during exams.[7]
In another study of individuals who had high cortisol responses to emotional stressors it was observed that the high cortisol responders were more likely to increase their calorie intake after being stressed when compared to those who had low cortisol reactions to stressful situations.[20] The choice of foods when under stress among those with high cortisol responses is also of interest as their tendencies were towards the consumption of high fat and calorically dense foods.[20] Several other human and animal studies confirm the observation that a high cortisol reaction to stress can accurately predict increased calorie intake under stress. With the food selection being high calorie foods that are high in fat and or sugar perhaps as a way to blunt their stress response and reduce feelings of anxiety. [21,22,23] An important factor that we will explore in greater detail in part 2 of our article on the relationship between stress induced eating & food addiction.
The Role Of Cortisol in Fat Accumulation
Not only does cortisol make us overeat- it also increases visceral abdominal fat accumulation.
Unfortunately, the problems with high cortisol reactivity doesn’t end with creating an environment conducive to overeating, as high cortisol levels may also be responsible for increased visceral abdominal fat accumulation.[24,25] Unlike subcutaneous fat located beneath the skin and muscles and which serves a role as a way of storing energy and maintaining body temperature, visceral abdominal fat is packed between your organs and is associated with increased risk of type 2 diabetes, insulin resistance, and cardiovascular disease.[26,27,28] 9,10,11- Wiki] While a tendency to consume more calories can and does increase body fat- abnormally high cortisol levels seem to influence fat distribution- as it makes our bodies store more intra-abdominal fat around the organs as opposed to subcutaneously. A highly controlled laboratory study found that women with high cortisol reactivity to stress have higher hip to waist ratios compared to those with low cortisol reactivity. Another study found that women who had higher cortisol responses to food intake had higher visceral abdominal fat distribution as compared to those who had normal cortisol responses, [29,30,31] so clearly there is a correlation between cortisol stress response and where and how body fat is stored.
There are several possible explanations, one being that there are far more glucocorticoid receptors in visceral abdominal fat compared to other regions [32], but cortisol also play a part in disrupting fat metabolism. Under normal conditions, cortisol appears to stimulate fat burning,[33] however when combined with high levels of insulin (as in the case of eating high sugar foods), increased cortisol levels do just the opposite and increase fat accumulation by stimulating the fat storage hormone lipoprotein lipase. Making matters even worse, cortisol also blunts the fat burning effects of growth hormone.[34,35] What is of concern is that the greater intra- abdominal fat perpetuates the cycle of fat accumulation as it also serves to produce more cortisol.[36] The reaction of a number of people in our population to stress is thus a poignant factor in the current number of obese individuals- and in the second installment of our series on stress and eating we will take a look at how this cycle can create a model of addictive behavior. Thanks as always for reading and do stay tuned for part two!
Read Part 2 Here: Food Addiction: Understanding The Science
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