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Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and other mammals, is increased to a point where it is associated with certain health conditions or increased mortality. Obesity is both an individual clinical condition and is increasingly viewed as a serious public health problem. Excessive body weight has been shown to predispose to various diseases, particularly cardiovascular diseases, diabetes mellitus type 2, sleep apnea, and osteoarthritis.[1]
Obesity is frequently the result of an addictive response to certain foods or eating behaviors. [4]
Cultural and social significanceEtymologyObesity is the nominal form of obese which comes from the Latin obēsus, which means "stout, fat, or plump." Ēsus is the past participle of edere (to eat), with ob added to it. In Classical Latin, this verb is seen only in past participial form. Its first attested usage in English was in 1651, in Noah Biggs's Matæotechnia Medicinæ Praxeos.[2] HistoryIn several human cultures, plumpness was associated with physical attractiveness, strength, and fertility. Some of the earliest known cultural artifacts, known as Venus figurines, are pocket-sized statuettes representing an obese female figure. Although their cultural significance is unrecorded, their widespread use throughout pre-historic Mediterranean and European cultures suggests a central role for the obese female form in magical rituals, and suggests cultural approval of (and perhaps reverence for) this body form. This is most likely due to their ability to easily bear children and survive famine. A large, well-fed body was occasionally considered a symbol of wealth and social status in cultures prone to food shortages or famine. Well into the early modern period in European cultures, it often served this role. But as food security was realized, it came to serve more as a visible signifier of "lust for life", appetite, and immersion in the realm of the erotic.
Contemporary cultureIn modern Western culture, the obese body shape came to be widely regarded as unattractive. Many negative stereotypes are commonly associated with obese people, such as the belief that they are lazy, stupid, or even evil, gluttony being the second of the seven deadly sins. Obese children, teenagers and adults face a heavy social stigma. Obese children are frequently the targets of bullies and are often shunned by their peers. Obesity in adulthood can lead to a slower rate of career advancement. Most obese people have experienced negative thoughts about their body image, and many take drastic steps to try to change their shape. Not all contemporary cultures disapprove of obesity. There are many cultures which are traditionally more approving (to varying degrees) of obesity, including some African, Arabic, Indian, and Pacific Island cultures. Especially in recent decades, obesity has come to be seen more as a medical condition in modern Western culture.[citation needed] Recently emerging is a small but vocal fat acceptance movement that seeks to challenge weight-based discrimination. Obesity acceptance and advocacy groups have initiated litigation to defend the rights of obese people and to prevent their social exclusion. Popular cultureImage:PigsisPigs1.jpg Obesity is often humorized in cartoons. Various stereotypes of obese people have found their way into expressions of popular culture. A common stereotype is the obese character who has a warm and dependable personality, but equally common is the obese vicious bully. (Dudley Dursley from the Harry Potter book series is a perfect example of this.) Gluttony and obesity are commonly depicted together in works of fiction. In cartoons, obesity is often used to comedic effect, with fat cartoon characters having to squeeze through narrow spaces, frequently getting stuck or even exploding. A more unusual example of obesity-related humour is Bustopher Jones, the fat cat, from the musical Cats, whose claim to fame is that he is a regular visitor to many gentlemen's clubs including Drones, Blimp's and the Tomb. Due to his constant lunching at these clubs, he is remarkably fat, "a twenty-five pounder... And he's putting on weight everyday." Another popular character, Garfield, a cartoon cat, is also obese for humor. When his owner, Jon, puts him on diets, rather than losing weight, Garfield slows down his weight gain. It can be argued that depiction in popular culture adds to and maintains commonly perceived stereotypes, in turn harming self esteem of obese people. A charge of discrimination on the basis of appearance could be leveled against these depictions.[citation needed] On the other hand, obesity is often associated with positive characteristics such as good humor (the stereotype of the jolly fat man like Santa Claus), and some people are more sexually attracted to obese people than to slender people (see chubby culture, fat admirer). Effects on healthObesity, especially central obesity (male-type or waist-predominant obesity), is an important risk factor for the "metabolic syndrome" ("syndrome X"), the clustering of a number of diseases and risk factors that heavily predispose for cardiovascular disease. These are diabetes mellitus type 2, high blood pressure, high blood cholesterol, and triglyceride levels (combined hyperlipidemia). An inflammatory state is present, which — together with the above — has been implicated in the high prevalence of atherosclerosis (fatty lumps in the arterial wall), and a prothrombotic state may further worsen cardiovascular risk. Apart from the metabolic syndrome, obesity is also correlated (in population studies) with a variety of other complications. For many of these complaints, it has not been clearly established to what extent they are caused directly by obesity itself, or have some other cause (such as limited exercise) that causes obesity as well. Most confidence in a direct cause is given to the mechanical complications in the following list:
While being severely obese has many health ramifications, those who are somewhat overweight face little increased mortality or morbidity. Some studies suggest that the somewhat "overweight" tend to live longer than those at their "ideal" weight. [5] This may in part be attributable to lower mortality rates in diseases where death is either caused or contributed to by significant weight loss due to the greater risk of being underweight experienced by those in the ideal category. Another factor which may confound mortality data is smoking, since obese individuals are less likely to smoke[citation needed]. Osteoporosis is known to occur less in slightly overweight people. MetricsIn the clinical setting, obesity is typically evaluated by measuring BMI (body mass index), waist circumference, and evaluating the presence of risk factors and comorbidities.[1] In epidemiological studies, BMI alone is used to define obesity. BMIBMI, or Body Mass Index, was developed by the Belgian statistician and anthropometrist Adolphe Quetelet.[5] It is calculated by dividing the subject's weight in kilograms by the square of his/her height in metres (<math>BMI = kg/m^2</math>) or (<math>BMI=weight (lbs.)*703/height(inches)^2</math>). The current definitions commonly in use establish the following values, agreed in 1997 and published in 2000:[6]
BMI is a simple and widely used method for estimating body fat.[9] In epidemiology BMI alone is used as an indicator of prevalence and incidence. BMI as an indicator of a clinical condition is used in conjunction with other clinical assessments, such as waist circumference. In a clinical setting, physicians take into account race, ethnicity, lean mass (muscularity), age, sex, and other factors which can affect the interpretation of BMI. BMI overestimates body fat in persons who are very muscular, and it can underestimate body fat in persons who have lost body mass (e.g. many elderly).[1] Mild obesity as defined by BMI alone is not a cardiac risk factor, and hence BMI cannot be used as a sole clinical and epidemiological predictor of cardiovascular health.[10] Waist circumferenceBMI does not take into account differing ratios of adipose to lean tissue; nor does it distinguish between differing forms of adiposity, some of which may correlate more closely with cardiovascular risk. Increasing understanding of the biology of different forms of adipose tissue has shown that visceral fat or central obesity (male-type or apple-type obesity) has a much stronger correlation, particularly with cardiovascular disease, than the BMI alone.[11] The absolute waist circumference (>102 cm in men and >88 cm in women) or waist-hip ratio (>0.9 for men and >0.85 for women)[11] are both used as measures of central obesity. Body fat measurementAn alternative way to determine obesity is to assess percent body fat. Doctors and scientists generally agree that men with more than 25% body fat and women with more than 30% body fat are obese. However, it is difficult to measure body fat precisely. The most accepted method has been to weigh a person underwater, but underwater weighing is a procedure limited to laboratories with special equipment. Two simpler methods for measuring body fat are the skinfold test, in which a pinch of skin is precisely measured to determine the thickness of the subcutaneous fat layer; or bioelectrical impedance analysis, usually only carried out at specialist clinics.[citation needed] Other measurements of body fat include computed tomography (CT/CAT scan), magnetic resonance imaging (MRI/NMR), and dual energy X-ray absorptiometry (DXA).[12] GestaltIn practice, for most examples of overweight that may designate risk, both doctor and patient can see "by eye" whether excess fat is a concern. In these cases, BMI thresholds provide simple targets all patients can understand.[13] Risk factors and comorbiditiesThe presence of risk factors and diseases associated with obesity are also used to establish a clinical diagnosis. Coronary heart disease, type 2 diabetes, and sleep apnea are possible life-threatening risk factors that would indicate clinical treatment of obesity.[1] Smoking, hypertension, age and family history are other risk factors that may indicate treatment.[1] Diabetes and heart disease are risk factors used in epidemiological studies of obesity. Recent research has been in the area of the relationship between obesity and addiction. There was a very interesting article on this topic in Science News Week of Sept. 3, 2005; Vol. 168, No. 10. Also, researchers at Harvard have been studying the relationship between binge eating and obesity, especially James I. Hudson, professor of psychiatry at Harvard Medical School and director of the Psychiatric Epidemiology Research Program at McLean Hospital announced results of study of binge eating disorder in February of 2007.http://www.thecrimson.com/article.aspx?ref=516775 CausesOvereatingIn its simplest conception, obesity is only made possible when the lifetime energy intake exceeds lifetime energy expenditure by more than it does for individuals of "normal weight". When food energy intake exceeds energy expenditure, fat cells (and to a lesser extent muscle and liver cells) throughout the body take in the energy and store it as fat. In all individuals, the excess energy utilized to generate fat reserves is minute relative to the total number of calories consumed. This means that very fine perturbations in the energy balance can lead to large fluctuations in weight over time. To illustrate, an obese 40 year old who carries 100 lb of adipose tissue has only consumed about 25 more calories per day than he has burned on average - or the equivalent of an apple every three days. In comparison a very lean 40-year-old who carries only 15 lb of body fat will have exceeded his daily energy expenditure by about four calories a day - the equivalent of an apple every 18 days.[citation needed] Additional factorsFactors that have been suggested to contribute to the development of obesity include:
As with many medical conditions, the caloric imbalance that results in obesity often develops from a combination of genetic and environmental factors. Polymorphisms in various genes controlling appetite, metabolism, and adipokine release predispose to obesity, but the condition requires availability of sufficient calories, and possibly other factors, to develop fully. Various genetic abnormalities that predispose to obesity have been identified (such as Prader-Willi syndrome and leptin receptor mutations), but known single-locus mutations have been found in only about 5% of obese individuals. While it is thought that a large proportion of the causative genes are still to be identified, much obesity is likely the result of interactions between multiple genes, and non-genetic factors are likely also important. Some eating disorders are associated with obesity, especially binge eating disorder (BED). As the name indicates, patients with this disorder are prone to overeat, often in binges. A proposed mechanism is that the eating serves to reduce anxiety, and some parallels with substance abuse can be drawn. An important additional factor is that BED patients often lack the ability to recognize hunger and satiety, something that is normally learned in childhood. Learning theory suggests that early childhood conceptions may lead to an association between food and a calm mental state. Tendencies of ethnic groupsCertain populations and individuals may be more prone to obesity than others, and the ability to take advantage of rare periods of abundance and use such abundance by storing energy efficiently was undoubtedly an evolutionary advantage in times when food was scarce. Individuals with greater adipose reserves were more likely to survive famine. This tendency to store fat is likely maladaptive in a society with adequate and stable food supplies. Neurobiological mechanismsImage:Fatmouse.jpg Scientists investigating the mechanisms and treatment of obesity may use animal models such as mice to conduct experiments. Flier[14] summarizes the many possible pathophysiological mechanisms involved in the development and maintenance of obesity. This field of research had been almost unapproached until leptin was discovered in 1994. Since this discovery, many other hormonal mechanisms have been elucidated that participate in the regulation of appetite and food intake, storage patterns of adipose tissue, development of insulin resistance. Since leptin's discovery, ghrelin, orexin, PYY 3-36, cholecystokinin, adiponectin, and many other mediators have been studied. The adipokines are mediators produced by adipose tissue; their action is thought to modify many obesity-related diseases. Leptin and ghrelin are considered to be complementary in their influence on appetite, with ghrelin produced by the stomach modulating short-term appetitive control (i.e. to eat when the stomach is empty and to stop when the stomach is stretched). Leptin is produced by adipose tissue to signal fat storage reserves in the body, and mediates long-term appetitive controls (i.e. to eat more when fat storages are low and less when fat storages are high). Although administration of leptin may be effective in a small subset of obese individuals who are leptin-deficient, many more obese individuals are thought to be leptin-resistant, and this resistance has been implicated in obesity in some people, is thought to explain in part why administration of leptin has not been shown to be effective in suppressing appetite in most obese subjects. Neuroscientific approaches hinge on the action of the aforementioned mediators on the hypothalamus, the part of the brain that is thought to process signals related to metabolic state and energy storage and to shift the energy balance in either a positive or negative direction, primarily by acting on appetite and energy expenditure. Lesion studies in the 1940s and 1950s identified two regions of the hypothalamus — the lateral hypothalamus (LH) and ventromedial hypothalamus (VMH) — as the brain's hunger and satiety centers, respectively. Specific lesions to a mouse's LH suppressed its appetite while damaging the VMH caused overeating. Studies of the distribution of the leptin receptor in the mid-1990s cast doubt upon this dual center theory of hunger and satiety. Leptin's effect on the arcuate nucleus melanocortin system is now considered central to the regulation of feeding and metabolism. Poverty linkSome obesity co-factors are resistant to the theory that the "epidemic" is a new phenomenon. In particular, a class co-factor consistently appears across many studies. Comparing net worth with BMI scores, a 2004 study[15] found obese American subjects approximately half as wealthy as thin ones. When income differentials were factored out, the inequity persisted — thin subjects were inheriting more wealth than fat ones. A higher rate of lack of education and tendencies to rely on cheaper fast foods is seen as a reason why these results are so dissimilar. Another study finds women who married into higher status are predictably thinner than women who married into lower status. TherapyThe mainstay of treatment for obesity is an energy-limited diet and increased exercise. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass on average (excluding study drop-outs). While not all dieters will be satisfied with this outcome, studies have shown that a loss of as little as 5% of body mass can create enormous health benefits. A more intractable therapeutic problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their body mass in studies, 80-95% will regain that weight within two to five years. It appears that the homeostatic mechanisms regulating body weight are very robust (see leptin, for example), and vigorously defend against weight loss. Much important research is now being devoted to determining what factors can improve the currently dismal weight loss maintenance rates. Recent scientific research has cast some doubt over whether or not dieting actually improves health, with some studies indicating that dieting may in fact be more detrimental than remaining overweight.[16] In a clinical practice guideline by the American College of Physicians,[17] the following five recommendations are made:
Much research focuses on new drugs to combat obesity, which is seen as the biggest health problem facing developed countries. Nutritionists and many doctors feel that these research funds would be better devoted to advice on good nutrition, healthy eating, and promoting a more active lifestyle. Medication most commonly prescribed for diet/exercise-resistant obesity is orlistat (Xenical, which reduces intestinal fat absorption by inhibiting pancreatic lipase) and sibutramine (Reductil, Meridia, an anorectic). In the presence of diabetes mellitus, there is evidence that the anti-diabetic drug metformin (Glucophage) can assist in weight loss — rather than sulfonylurea derivatives and insulin, which often lead to further weight gain. The thiazolidinediones (rosiglitazone or pioglitazone) can cause slight weight gain, but decrease the "pathologic" form of abdominal fat, and are therefore often used in obese diabetics. Increasingly, bariatric surgery is being used to combat obesity. The most common weight loss surgery in Europe and Australia is the adjustable gastric band where a silicone ring is placed around the top of the stomach to help restrict the amount of food eaten in a sitting. This surgery has been FDA approved in the United States since 2001 but has been being used in other parts of the world since the early 1990s. It is considered the safest and least invasive of the available weight loss surgeries such as Roux-en-Y gastric bypass surgery (RNY), biliopancreatic diversion, and stomach stapling (also known as "vertical banded gastroplasty", VBG). Unlike those more invasive techniques the band surgery does not cut into or reroute any of the digestive tract and is completely reversible. Removing the implant returns the stomach to its pre-surgical norm. All of these surgeries can be done laparoscopically. The more invasive of the surgeries usually bypass or remove some portion of the patient's intestines which causes malabsorption and dumping. All of these surgeries come with risk to the patient. For instance a recent study by the U.S. Department of Health and Human Service showed a 40% complication rate within 180 days of bariatric surgery.[18] Moreover these surgeries do not guarantee either successful weight loss or reduced morbidity and mortality. Patients are also required to make lifelong changes to their diet if they are to keep the lost weight off in the long term. Therefore, as with any major surgery, patients needs to carefully evalute the long term ramifications of their choice. Public health and policyImage:Bmi30chart.png Graphic chart comparing obesity percentages of the total population in OECD member countries. Prevalence
The Health Survey for England predicts that more than 12 million adults and 1 million children will be obese by 2010 if no action is taken.[19][20] The prime minister has urged people to take more responsibility for their fitness and diet.[21]
The prevalence of overweight and obesity in the United States makes obesity a leading public health problem. The United States has the highest rates of obesity in the developed world. From 1980 to 2002, obesity has doubled in adults and overweight prevalence has tripled in children and adolescents.[22] From 2003-2004, "children and adolescents aged 2 to 19 years, 17.1% were overweight...and 32.2% of adults aged 20 years or older were obese."[22] The prevalence in the United States continues to rise.[22] The prevalence of obesity has been continually rising for two decades.[23] This sudden rise in obesity prevalence is attributed to environmental and population factors rather than individual behavior and biology because of the rapid and continual rise in the number of overweight and obese individuals.[24] The current environment produces risk factors for decreased physical activity and for increased calorie consumption. These environmental factors operate on the population to decrease physical activity and increase calorie consumption. Environmental factorsWhile it may often appear obvious why a certain individual gets fat, it is far more difficult to understand why the average weight of certain societies have recently been growing. While genetic causes are central to understanding obesity, they cannot fully explain why one culture grows fatter than another. This is most notable in the United States. In the years from just after the Second World War until 1960 the average person's weight increased, but few were obese. In the two and a half decades since 1980 the growth in the rate of obesity has accelerated markedly and is increasingly becoming a public health concern. There are a number of theories as to the cause of this change since 1980. Most believe it is a combination of various factors.
Interestingly an increase in the number of Americans who exercise and diet occurred before the increase in obesity, and some scholars have even argued that these trends actually encouraged obesity. Nearly all diets fail, with participants resuming their previous eating habits or even engaging in binge eating. Many then see an overall increase in their weight. If the diet is then repeated and abandoned again, a pattern of rising and falling weight is established, known as weight cycling. Similarly those who work out but then stop can end up being heavier than those who never exercised. Public health and policy responsesOn top of controversies about the causes of obesity, and about its precise health implications, come policy controversies about the correct approach to obesity. The main debate is between "personal responsibility" advocates, who resist regulatory attempts to intervene in citizen's private dietary habits, and "public interest" advocates, who promote regulations, on the same public health grounds as the restrictions applied to tobacco products. In the U.S., a recent bout in this controversy involves the so-called Cheeseburger Bill, an attempt to indemnify food industry businesses from what some consider to be frivolous lawsuits by obese clients. "Personal responsibility" advocates work on the basis that, as the microbiologist Rene Dubos once said, health ought not to be considered an end in itself, but "the condition best suited to reach goals that each individual formulates for himself" [8]. Any other definition permits authorities to curtail the autonomy of the self-determining individual, imposing quantity over quality of life onto them, undermining his civil liberties. As much as principled doctors, personal responsibility arguments have also been offered by food producer lobbies. In 1961, for example, as President John F Kennedy raised concerns about a lack of fitness in American society, a spokesman for the U.S. Dairy industry, Frank R. Neu, wrote advertorials warning We May Be Sitting Ourselves To Death.[28] Not food regulation, but personal exercising, is mooted as the solution. When it comes to childhood obesity, personal responsibility also means parental responsibility. A survey by the nonpartisan group Public Agenda found 68 percent of American parents said it was "absolutely essential" to teach their children good eating habits, but only 40 percent believe they had succeeded. Fewer parents say it is essential to teach their children about physical fitness (51 percent), but more believe they have succeeded (53 percent). Overall, parents said they found it difficult to protect their children from negative social messages on a range of topics, including bad nutrition.[29] On July 15, 2004, the United States Department of Health and Human Services announced a new policy from HHS' Centers for Medicare & Medicaid Services (CMS) removing language in the Medicare Coverage Issues Manual stating that obesity is not an illness. According to the press release "This step allows members of the public to request that Medicare review medical evidence to determine whether specific treatments related to obesity would be covered by Medicare. By law, Medicare covers specified medically necessary services for illness and injury. The prior manual language, because it stated that obesity was not an illness, could prevent Medicare from covering treatments for diseases related to obesity."[30] Non-medical consequencesBesides increases in disease and mortality there are other implications of the present world trend in obesity. Among these are:
See also
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