Extreme overweight, with an excessive amount of body fat; the most common nutritional disease in affluent societies. It is associated with a high mortality, and predisposes to serious diseases, including diabetes mellitis, hypertension, and coronary heart disease. It may be related to genetic factors, or to hormonal disorders such as hypothyroidism, or Cushing's syndrome. However the majority of cases are a consequence of excessive food intake and inadequate physical exercise.
ObesityClassifications and external resources
| An obese man. | ||
| ICD-9 | 278 | |
| DiseasesDB | 9099 | |
| MedlinePlus | 003101 | |
| eMedicine | med/1653 | |
| MeSH | C23.888.144.699.500 | |
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 a risk factor for certain health conditions or increased mortality. Obesity develops from the interaction of individual biology and the environment. Obesity is both an individual clinical condition and is increasingly viewed as a serious public health problem.
Definition
In the clinical setting, obesity is typically evaluated by measuring BMI (body mass index), waist circumference, and evaluating the presence of risk factors and comorbidities. In epidemiological studies BMI alone is used to define obesity.
BMI
BMI, or Body Mass Index, was developed by the Belgian statistician and anthropometrist Adolphe Quetelet.
The current definitions commonly in use establish the following values, agreed in 1997 and published in 2000:
A BMI less than 18.5 is underweight A BMI of 18.5 - 24.9 is normal weight A BMI of 25.0 - 29.9 is overweight A BMI of 30.0 - 39.9 is obese A BMI of 40.0 or higher is severely (or morbidly) obeseBMI is a simple and widely used method for estimating body fat.
BMI as an indicator of a clinical condition is used in conjunction with other clinical assessments, such as waist circumference. 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. 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.
Waist circumference
BMI does not take into account differing ratios of adipose to lean tissue; 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.
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) are both used as measures of central obesity.
Body fat measurement
An 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.
Gestalt
In practice, for most examples of overweight that may designate risk, both doctor and patient can see "by eye" whether excess fat is a concern.
Risk factors and comorbidities
The 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. Diabetes and heart disease are risk factors used in epidemiological studies of obesity.
Causes
Causative factors
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 its simplest conception, therefore, obesity is only made possible when the lifetime energy intake exceeds lifetime energy expenditure by more than it does for individuals of "normal weight".
In all individuals, the excess energy utilized to generate fat reserves is minute relative to the total number of calories consumed. 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.
Factors that have been suggested to contribute to the development of obesity include:
Genetic factors and some genetic disorders (e.g., Prader-Willi syndrome) Underlying illness (e.g. hypothyroidism) Certain medications (e.g., atypical antipsychotics) Sedentary lifestyle A high glycemic diet (i.e., a diet that consists of meals that give high postprandial blood sugar) Weight cycling, caused by repeated attempts to lose weight by dieting Eating disorders (such as binge eating disorder) Stressful mentality Insufficient sleep Smoking cessationAs 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).
Evolutionary aspects
Although there is no definitive explanation for the recent increase of obesity, the thrifty gene hypothesis provides some understanding of this phenomenon, and suggests why certain populations and individuals may be more prone to obesity than others.
Neurobiological mechanisms
Flier summarizes the many possible pathophysiological mechanisms involved in the development and maintenance of obesity.
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. 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.
Studies of the distribution of the leptin receptor in the mid-1990s cast doubt upon this dual center theory of hunger and satiety.
Poverty link
Some obesity co-factors are resistant to the theory that the "epidemic" is a new phenomenon. Comparing net worth with BMI scores, a 2004 study found obese American subjects approximately half as wealthy as thin ones.
Complications
Obesity, 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.
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. Respiratory: dyspnea, obstructive sleep apnea, hypoventilation syndrome, Pickwickian syndrome, asthma Psychological: Depression, low self esteem, body dysmorphic disorder, social stigmatization
While being severely obese has many health ramifications, those who are somewhat overweight face little increased mortality or morbidity. 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.
Therapy
The 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).
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.
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.
In a clinical practice guideline by the American College of Physicians, the following five recommendations are made:
People with a BMI of over 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss. For more severe cases of obesity, stronger drugs such as amphetamine and methamphetamine may be used on a selective basis.Much research focuses on new drugs to combat obesity, which is seen as the biggest health problem facing developed countries.
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.
All of these surgeries come with risk to the patient.
Cultural and social significance
Etymology
Obesity is the nominal form of obese which comes from the Latin obēsus, which means "stout, fat, or plump."
History and obesity
In several human cultures, obesity 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.
Obesity was occasionally considered a symbol of wealth and social status in cultures prone to food shortages or famine. Obesity can also be seen as a symbol within a system of prestige.
Contemporary culture
In modern Western culture, the obese body shape is widely regarded as unattractive. Obese bodies are rarely positively represented in mainstream media. Many negative stereotypes are commonly associated with obese people, such as the belief that they are lazy, dirty, stupid, or even evil. 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.
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 culture
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. 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.
It can be argued that depiction in popular culture adds to and maintains commonly perceived stereotypes, in turn harming self esteem of obese people.
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).
Public health and policy
Prevalence
United KingdomThe 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.
United StatesThe 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. 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." The prevalence of obesity has been continually rising for two decades. 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.
Environmental factors
While 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.
Lack of activity: obese people appear to be less active in general than lean people, and not just because of their obesity. correspondingly when obese people lost weight they did not become more active. Urban sprawl may be a factor: obesity rates increase as urban sprawl increases, possibly due to less walking and less time for cooking. Increasing affluence itself (including many of the above factors as accompaniments of affluence) may be a cause, or contributing factor since obesity tends to flourish as a disease of affluence in countries which are developing and becoming westernised . U.S. obesity statistics followed the same pattern, offset by two years. An aging population may also be a major factor, as the likelihood of becoming obese increases with age. Beyond their twenties, the older a person becomes the slower their metabolism becomes, reducing the amount of calories required to sustain the body, thus if a person does not reduce their intake of food with age, they will become obese over time. As the average age of individuals within a society increases, the rate of obesity also increases. This situation is exacerbated by the baby boom generation, which represents a disproportionately large portion of the population in many countries and is currently nearing the latter end of the typical lifespan in affluent nations, and therefore is in the high-risk zone for obesity.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. If the diet is then repeated and abandoned again, a pattern of rising and falling weight is established, known as weight cycling.
Public health and policy responses
On top of controversies about the causes of obesity, and about its precise health implications, come policy controversies about the correct approach to obesity. 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" .
When it comes to childhood obesity, personal responsibility also means parental responsibility.
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. The prior manual language, because it stated that obesity was not an illness, could prevent Medicare from covering treatments for diseases related to obesity."
Non-medical consequences
Besides increases in disease and mortality there are other implications of the present world trend in obesity. (Extra weight of obese passengers is costing airlines and consumers US$275,000,000 per annum.) Increased litigation by obese persons suing restaurants (over causation of obesity) and airlines (over airline seating width) . Note that the Personal Responsibility in Food Consumption Act of 2005 was motivated by a need to reduce litigation from obesity activists. Sizeable societal economic costs attributable to obesity, with medical costs attributable to obesity rising to 78.5 billion dollars or 9.1 percent of all medical expenditures in the U.S. as of 1998. However, such studies do not necessarily consider that earlier mortality of obese people may save health costs associated with aging.
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