Tuesday, May 08, 2007

Comfort Food and Stress Study

Dallman MF, Pecoraro N, et al. (2003) Chronic stress and obesity: a new view of "comfort food". Proceedings of the National Academy of Sciences Sep 30; 100(20): 11696-701.

The body reacts to stress by releasing catecholamines and glucocorticoids (GCs), hormones that control a major part of the autonomic nervous system. The Hypothalamic-Pituitary-Adrenal (HPA) axis is also a major aspect of this system, since its primary role is to balance the stress hormones mentioned above. This study's main objective was to observe how chronic stress plays a role in obesity, particularly in how chronically high levels of GCs act in three ways to cause the individual to rely upon "comfort foods," which are higher in refined carbohydrate and saturated fat. Those three ways include: one, high amounts of CRF in the amygdala; two, high stimulus salience of activities; and three, high abdominal obesity, which lowers HPA activity.

Although this study used rats as its main subjects to analyze the above three ways, the authors state that the effects of chronic stress and GCs in rats do indeed apply to humans, as well. In the first way, GCs will increase the expression of CRF (corticotropin-releasing factor) in the amygdala (the node in the emotional part of the brain). The high expression of CRF induces us to draw from "the chronic stress network" pool, which increases ACTH and corticosterone B, both hormones that respond to acute stressors and increase anxiety-like behavior. In addition, recruiting this chronic stress network over time will increase the PVT (paraventricular thalamus) secretion of glutamate, which is said to increase synaptic connections. My postulation is that drawing from the chronic stress network pool over time will deplete the components necessary to confront stressful situations, which in turn, can cause compulsive activity since the response network won't be as efficient.

The second way that chronic GC affects our bodies is via a high stimulus salience of activities, which includes exactly what I postulated—namely compulsive activity. This study defined compulsive activity as ingesting sucrose, fat, drugs and wheel-running. They found that corticosterone B specifically raised consumption of comfort foods when rats were chronically stressed, which is again, due to high GCs causing an excitatory response in the brain. With comfort food, HPA axis activity declines, meaning that the ability for the body to balance its stress hormones is greatly reduced. As a result, to lead into the third way that was mentioned, the body responds with a build-up of abdominal fat depots, which increases the inhibitory feedback signal of CRF. Since CRF receptors lie in the amygdala, this emotional cycle can continue and lead to obesity if stress levels are left unchecked.

What is essential to note is the decrease in HPA axis activity, since we decrease the ability to balance our GCs and catecholamines. In turn, the inability to balance these hormones properly can impel one to look to outside mechanisms, such as the comfort foods, the drugs, etc, to regulate the internal chaos. Ironically, eating these foods and/or doing drugs only worsens the havoc within the body, and the cycle continues. The study's authors suggest that attempting to reduce stress in one's life can help to mitigate the effects of our chronic stress-response network, and can help to improve overall mental and physical health.

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