Structured stress and the US obesity epidemic--论文代写范文精选

儿童期体重过重是在美国迅速上升,尤其是在非裔美国人和拉美裔美国人。到1998年患病率增加到21.5%。肥胖症与严重疾病包括糖尿病,心脏病,高血压。下面的essay代写范文进行讲述。

Abstract 
We examine the accelerating ‘obesity epidemic’ in the US from the perspective of recently developed theory relating a cognitive hypothalamicpituitary-adrenal axis to an embedding ‘language’ of structured psychosocial stress. Using a Rate Distortion argument, the obesity epidemic is found to represent the literal writing of an image of a ratcheting pathological social hierarchy onto the bodies of American adults and children. This process, while stratified by the usual divisions of class and ethnicity, is nonetheless relentlessly engulfing even affluent majority populations. Our perspective places the common explanation that ‘obesity occurs when people eat too much and get too little exercise’ in the same category as the remark by US President Calvin Coolidge on the eve of the Great Depression that ‘unemployment occurs when large numbers of people are out of work’. Both statements ignore profound structural determinants of great population suffering which must be addressed by collective actions of equally great reform.

Introduction 
Obesity is epidemic in the United States, has been so for more than two decades, and continues to increase. Current rates of overweight and obesity in the US are 61% and 14% in adults and children respectively. Obesity in adults has nearly doubled since 1980, from 15% in 1980 to 27% by 1999 (e.g. Wellman and Friedberg, 2002). Childhood overweight is rapidly rising in the US, particularly among African Americans and Hispanics. By 1998 prevalence increased to 21.5% in African Americans, 21.8% among Hispanics, and 12.3% among non-Hispanic whites aged 4 to 12 years (Strauss and Pollack, 2001). The obesity epidemic is associated with serious health conditions including type 2 diabetes, heart disease, high blood pressure and stroke, certain types of cancer, hypoxia, sleep apnea, hernia, and arthritis. It is a major cause of economic loss, death, and suffering which shows no indications of abatement. 

Abdominal obesity and visceral fat accumulation are particularly associated with disease, and have become the focus of much research on ‘stress’ and its relation to the ‘fight-or-flight’ responses of the hypothalamic-pituitaryadrenal (HPA) axis. We paraphrase Bjorntorp (2001), who extensively summarizes the role of the HPA axis in physiological responses to stress. When the input of noxious signals is prolonged, the HPA axis reactivity changes from normal and relatively transient attempts to maintain homeostasis or allostasis with temporary peaks of cortisol secretion first, to a state of sensitization, which reacts with exaggerated cortisol secretion after a given input. 

This occurs during the most active phase of the HPA axis, which is the early morning in humans. When repeated too often and with sufficient strength of the input, the first sign of malfunction is a delayed down-winding, so that cortisol secretion stays elevated for a prolonged period of time. Subsequently, the normal diurnal pattern is disrupted, and morning values tend to be lower. This subsequently develops into a low, steady, rigid diurnal cortisol secretion with little reactivity, a ‘burned out’ HPA. In parallel, the controlling, central glucocorticoid receptors become less efficient, and down-regulated. Further challenges are followed by atrophy of the entire system, often found after long-term, severe hypercortisolaemia as in Cushing’s syndrome, melancholic depression, post traumatic stress disorder (PTSD), and the aftermath of war. 

Bjorntorp (2001) describes how elevation of cortisol is followed by visceral fat accumulation. Much research shows consequent lowered sex steroid and growth hormone secretions have the same consequence, because of the insufficient counteraction against cortisol effects, and the combination of these abnormalities powerfully directs a larger than normal fraction of total body fat to visceral deposits. In sum, increased activity of the HPA axis triggers both inhibition of both the pituitary gonadal and growth hormone axes. 

Stress may, then, synergistically cause accumulation of visceral fat, via elevated cortisol secretion and decrease of sex steroid and growth hormones. Bjorntorp concludes in particular that the deposit of central body fat, which is closely correlated with general measures of obesity, can serve as a reasonable approximation to the long-term endocrine abnormalities associated with stress and often-repeated or chronic activation of the HPA axis. That is, stress literally writes an image of itself onto the body as visceral fat accumulation, first having written an image of itself onto the HPA axis. The phenomenon can be interpreted as the transmission of a structured signal between communicating systems, in a large sense, i.e. psychosocial to HPA. Here we will adapt recent developments regarding the punctuated information dynamics of evolutionary process to the question of how the communication of the embedding psychosocial structure and the HPA axis might be constrained by certain of the asymptotic limit theorems of probability. 

We know that, regardless of the distribution of a particular stochastic process, the Central Limit Theorem ensures that long sums of independent realizations of that process will follow a Normal distribution. Similar constraints exist on the behavior of communicating structures, and are described by the limit theorems of information theory. Importation of phase transition methods from statistical physics, done much in the spirit of the Large Deviations Program of applied probability, permits concise and unified description of evolutionary and cognitive ‘learning plateaus’ which, in the evolutionary case, are interpreted as evolutionary punctuation (e.g. Wallace, 2002a, b).

‘Stress’, we aver, is not often random in human societies, but is rather a highly structured ‘language’, having both a grammar and a syntax, so that certain stressors are ‘meaningful’ in a particular context, and others are not, having little or no long-term physiological effect. We will argue that the HPA axis is, in fact, a cognitive system itself associated with a ‘dual information source’ which may also be expressed as a kind of language. It is the punctuated interaction of these two ‘languages’ which we will find critical to an understanding of how psychosocial stress affects the HPA axis, and, ultimately, writes a distorted image of itself on the human body as visceral fat deposition. This analysis presents a slightly different picture of the obesity epidemic, but one having profound implications for intervention policy.（essay代写)

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