Obesity has been connected to mental health problems in several studies. There have been studies on laboratory animals like rats and mice that show that stress can, in some cases, lead to increases and in yet other cases to decreases in food intake.
Stress and weight in rats
In rats, however, decreased food intake and weight loss is a more reliable marker of stress severity than weight gain.
Studies have also shown that if the stressed rats are given a choice of highly palatable food, such as lard or sugar, their stress raises intake of palatable food specifically and causes weight gain.
Stress and food choices in humans
Studies in humans show that stress in around 30% of the population decreases food intake and induces loss of weight. In the same situation as the rats presented with palatable foods, it has been hypothesized that most humans in the Westernized countries live in a palatable food environment. There is an abundance of calorically dense food. This drives a majority of the population to eat more of these calorie rich foods when stressed.
Coping with stress
Studies among Americans for example show that nearly 50% of the population engage in unhealthy behaviors such as smoking as well as overeating to cope with stress. This is more common among women than men.
The concept of “comfort eating” especially driven by stress is thus an important one in the face of the growing obesity epidemic.
Pathology behind stress, comfort eating and obesity
Studies show that continued stress leads to increased levels of the stress hormone cortisol in the body. The brain contains a reward centre or pleasure centre that is gratified with highly palatable foods and other pleasurable experiences.
High levels of cortisol cause sensitization of the reward system leading to excessive intake of highly palatable food. The combination of high levels of cortisol and calorie rich foods leads to high insulin and finally fat deposition around the abdomen.
Features of an acute stress response
During an acute stress response there are several key features that include:-
increased heart rate and blood pressure
use of the blood to fuel the muscles, heart and the brain
slowing of digestion and other features such as decreased libido
suppression of appetite and food intake
While there is a chance of suppression of appetite during acute stress, it does not happen in many individuals where acute stress may lead to overeating.
Stress and the HPA axis
Stress leads to the activation of the hypothalamus pituitary adrenal (HPA) axis and the sympathetic–adrenomedullary (SAM) system. When there is stress the Corticotropin-releasing hormone (CRH) neurons in the hypothalamus initiate the stress response.
CRH stimulates the secretion of ACTH from the anterior pituitary. Adrenocorticotropic hormone (ACTH) in turn acts on the zona fasciculata of the adrenal cortex where it stimulates the release of cortisol or corticosterone.
High levels of cortisol in turn stop further stimulation of the brain to release cortisol in a negative feedback system. This is the HPA axis. The HPA axis and its negative feedback prevents long term cortisol exposure. The SAM activates the adrenal and releases Adrenaline. Cortisol induces eating while adrenaline suppresses eating.
Stress may be of two types
threat stress when the person perceives the situation to be a sure failure
challenge stress where the situation is demanding but controllable
Threat stress leads to increased activation of SAM over HPA axis and it is vice versa with challenge stress. Thus challenge stress leads to increased feeding and is linked to obesity.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)