ओबेसिटी

ओबेसिटी
"वर्गीकरण व पिनेयागु श्रोत"
Silhouettes and waist circumferences representing normal, overweight, and obese.
ICD-10 E66.
ICD-9 278
DiseasesDB 9099
मेडलाइन प्लस 003101
ईमेडिसिन med/1653
MeSH C23.888.144.699.500

ओबेसिटी छगू अवस्था ख। थ्व अवस्थाय् म्हय् दा अप्वया उसाँय्‌य् प्रतिकूल असर यायेगु क्षमता तै। [१] Obesity is commonly defined as a body mass index (BMI) of 30 kg/m2 or higher.[१] This definition distinguishes obesity from being pre-obese or overweight, which is classified as a BMI of 25 kg/m2 but less than 30 kg/m2.[१]

Excessive body weight is associated with various diseases, particularly cardiovascular diseases, diabetes mellitus type 2, obstructive sleep apnea, certain types of cancer, and osteoarthritis.[२][३] As a result, obesity has been found to reduce life expectancy.[३] A combination of excessive caloric intake, lack of physical activity, and genetic susceptibility is thought to explain most cases of obesity, with a limited number of cases due solely to genetics, medical reasons, or psychiatric illness.

The primary treatment for obesity is dieting and physical exercise. If this fails, anti-obesity drugs and (in severe cases) bariatric surgery may be attempted.[२][४]

As obesity is one of the leading preventable causes of death worldwide and with rates of adult and childhood obesity increasing, authorities view it as one of the most serious public health problems of the 21st century.[५] Obesity is often stigmatized in the modern Western world. However, it has been perceived as a symbol of wealth and fertility at other times in history and still is in many parts of Africa.[३][६]

Classification

An obese male with a body mass index of 46 kg/m2. Weight 146 kg (322 lbs), height 177 cm (5 ft 10 in)

Obesity, in absolute terms, is an increase of body adipose (fat tissue) mass.[१] In a practical setting this is difficult to determine directly and therefore, the common clinical methods used to estimate obesity are by body mass index (BMI) and in terms of its distribution via the waist–hip ratio.[७] The presence of obesity needs to be evaluated in the context of other risk factors such as medical conditions that could influence the risk of complications.[२]

Body fat percentage

मू पौ: Body fat percentage
On the left an abdominal CT of a person of normal weight. On the right an abdominal CT of an obese person. Note is made of 3.6 cm of subcutaneous fat.

Body fat percentage is total body fat expressed as a percentage of total body weight. It is generally agreed that men with more than 25% body fat and women with more than 33% body fat are obese.[८] Body fat percentage can be estimated from a person's BMI by the following formula:

$Body fat % = (1.2*BMI)+(0.23*age)-5.4-(10.8*gender)$
where gender is 0 if female and 1 if male

This formula takes into account the fact that body fat percentage is 10% greater in women than in men for a given BMI. It recognizes that a person's percentage body fat increases as they age even if their weight remains constant. The results have an accuracy of 4%.[९]

Direct attempts to determine body fat percent are difficult and often expensive. One of the most accurate methods is to weigh a person underwater which is known as hydrostatic weighing. Two other simpler and less accurate methods for measuring body fat therefore have historically been used. The first is the skinfold test, in which a pinch of skin is precisely measured to determine the thickness of the subcutaneous fat layer. It has not, however, been adequately evaluated in obese subjects.[९] The other is bioelectrical impedance analysis which uses electrical resistance. Bioelectrical impedance however has not been shown to provide an advantage over BMI. Therefore the routine use of these tests are discouraged.[४]

Body fat percentage measurement techniques used mainly for research include computed tomography (CT scan), magnetic resonance imaging (MRI), and dual energy X-ray absorptiometry (DEXA).[१०] These techniques provide very accurate measurements, but it can be difficult to scan the severely obese due to weight limits of the equipment and insufficient diameter of the CT or MRI scanner.[९]

BMI

मू पौ: Body mass index

Body mass index or BMI is a simple and widely used method for estimating body fat mass.[११] BMI was developed in the 19th century by the Belgian statistician and anthropometrist Adolphe Quetelet.[१२] BMI is an accurate reflection of body fat percentage in the majority of the adult population. It is less accurate in people such as body builders and pregnant women in whom body composition is affected.[२]

BMI Classification
Less than 18.5 underweight
18.5–24.9 normal weight
25.0–29.9 is overweight
30.0–34.9 is class I obesity
35.0–39.9 class II obesity
Over 40.0   class III obesity

BMI is calculated by dividing the subject's mass by the square of his or her height, typically expressed either in metric or US "Customary" units:

Metric: $BMI=kilograms/meters^2$
US/Customary and imperial: $BMI=lb*703/in^2$

where $lb$ is the subject's weight in pounds and $in$ is the subject's height in inches.

The most commonly used definitions, established by the WHO in 1997 and published in 2000, provide the values listed in the table at right.[१]

Some modifications to the WHO definitions have been made by particular bodies. The surgical literature breaks down "class III" obesity into further categories.[१३]

• Any BMI > 40 is severe obesity
• A BMI of 40.0–49.9 is morbid obesity
• A BMI of >50 is super obese

As Asian populations develop negative health consequences at a lower BMI than Caucasians, some nations have redefined obesity. The Japanese have defined obesity as any BMI greater than 25[१४] while China uses a BMI of greater than 28.[१५]

Waist circumference and waist–hip ratio

मू पौ: Central obesity

The absolute waist circumference (>102 cm in men and >88 cm in women) and the waist–hip ratio (the circumference of the waist divided by that of the hips of >0.9 for men and >0.85 for women) are both used as measures of central obesity.[१६]

In those with a BMI under 35, intra-abdominal body fat is related to negative health outcomes independent of total body fat.[१०] Intra-abdominal or visceral fat has a particularly strong correlation with cardiovascular disease.[१६] In a study of 15,000 subjects, waist circumference also correlated better with metabolic syndrome than BMI.[१७] Women who have abdominal obesity have a cardiovascular risk similar to that of men.[१८] In people with a BMI over 35, measurement of waist circumference however adds little to the predictive power of BMI as most individuals with this BMI have an abnormal waist circumferences.[२]

Childhood obesity

Children with various degrees of body fat
मू पौ: Childhood obesity

The healthy BMI range varies with the age and sex of the child. Obesity in children and adolescents is defined as a BMI greater than the 95th percentile.[१९] The reference data that these percentiles are based on is from 1963 to 1994 and thus has not been affected by the recent increases in rates of obesity.[२०]

Childhood obesity has reached epidemic proportions in 21st century with rising rates in both the developed and developing world. Rates of obesity in Canadian boys have increased from 11% in 1980s to over 30% in 1990s, while during this same time period rates increased from 4% to 14% in Brazilian children.[२१]

As with obesity in adults many different factors contribute to the rising rates of childhood obesity. Changing diet and decreasing physical activity are believed to be the two most important in causing the recent increase in the rate of obesity. Physical activity among children in activities from self propelled transport, to school physical education, and organized sports has been declining in many countries.[२२] Treatments used in children are primarily lifestyle interventions and behavioral techniques. Medications are not FDA approved for use in this age group.[२१]

Effects on health

Excessive body weight is associated with various diseases, particularly cardiovascular diseases, diabetes mellitus type 2, obstructive sleep apnea, certain types of cancer, and osteoarthritis.[२][३] As a result, obesity has been found to reduce life expectancy.[३]

Mortality

Obesity is one of the leading preventable causes of death worldwide.[२३][२४][२५] Large scale American and European studies have found that mortality risk varies with BMI; the lowest risk is found at a BMI of 22.5 - 25 kg/m2[२६] in non smokers and at a BMI of 24-27 kg/m2 in current smokers and increases with changes in either direction.[२७][२८] Obesity increases the risk of death in current and former smokers as well as in those who have never smoked.[२८] A BMI of over 32 has been associated with a doubled mortality rate among women over a 16 year period[२९] and obesity is estimated to cause an excess 111,909 to 365,000 death per year in the United States.[२५][३] Obesity on average reduces life expectancy by 6–7 years.[३०][३] A BMI of 30 - 35 reduces life expectancy by 2—4 years[२६] while severe obesity (BMI >40) reduces life expectancy by 20 years for men and 5 years for women.[८]

Morbidity

A number of physical and mental conditions have been associated with obesity. These commodities are reflected predominantly in metabolic syndrome.[३] Metabolic syndrome is a combination of medical disorders, which includes diabetes mellitus type 2, high blood pressure, high blood cholesterol, and high triglyceride levels.[३१]

Obesity is related to a variety of other complications as well. Some of these are directly caused by obesity and others are indirectly related through mechanisms sharing a common cause such as poor diet or a sedentary lifestyle. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with type 2 diabetes. Excess body fat is behind 64% of cases of diabetes in men and 77% of cases in women.[९]

Health consequences can be categorized by the effects of increased fat mass (osteoarthritis, obstructive sleep apnea, social stigmatization) or by the increased number of fat cells (diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease).[३][३२] Increases in body fat alter the body's response to insulin, potentially leading to insulin resistance. Increased fat also creates a proinflammatory state, increasing the risk of thrombosis.[३२]

Medical field Condition Medical field Condition
Cardiology Dermatology
Endocrinology and Reproductive medicine Gastrointestinal
Neurology Oncology[४३]
Psychiatry Respirology
Rheumatology and Orthopedics Urology and Nephrology

Although the negative health consequences of obesity in the general population are well supported by the available evidence, health outcomes in certain subgroups seem to be improved at an increased BMI, a phenomenon known as the obesity survival paradox.[५३] The paradox was first described in 1999 in overweight and obese patients undergoing hemodialysis. Since then it has been found in a few other subgroups and explanations for its occurrence have been put forward.[५३]

In people with heart failure, those with a BMI between 30.0–34.9 had lower mortality then those with a normal weight. This has been attributed to the fact that people often lose weight as they become progressively more ill.[५४] Similar findings have been made in other types of heart disease. People with class I obesity and heart disease do not have greater rates of further heart problems than people of normal weight who also have heart disease. In people with greater degrees of obesity, however, risk of further events is increased.[५५][५६] Even after cardiac bypass surgery, no increase in mortality is seen in the overweight and obese.[५७] One study found that the increased survival could be explained by the more aggressive treatment obese people receive after a cardiac event.[५८]

Causes

At an individual level, a combination of excessive caloric intake, lack of physical activity, and genetic susceptibility is thought to explain most cases of obesity, with a limited number of cases due solely to genetics, medical reasons, or psychiatric illness.[५९][६०] On a societal level increasing rates of obesity are felt to be due to an easily accessible and palatable diet,[६१] increased reliance on cars, and mechanized manufacturing.[६२][६३]

A 2006 review identifies ten other possible contributors to the recent increase of obesity: (1) insufficient sleep, (2) endocrine disruptors (environmental pollutants that interfere with lipid metabolism), (3) decreased variability in ambient temperature, (4) decreased rates of smoking, because smoking suppresses appetite, (5) increased use of medications that can cause weight gain (e.g., atypical antipsychotics), (6) proportional increases in ethnic and age groups that tend to be heavier, (7) pregnancy at a later age (which may cause susceptibility to obesity in children), (8) epigenetic risk factors passed on generationally, (9) natural selection for higher BMI, and (10) assortative mating leading to increased concentration of obesity risk factors (this would not necessarily increase the number of obese people, but would increase the average population weight).[६४] There is substantial but not conclusive evidence for these mechanisms, and the authors specify that they are probably less influential than the ones discussed in the previous paragraph (but still important).

Diet

 Map of dietary energy availability per person per day in 1979-1981 (kcal/person/day).[६५]      no data      <1600      1600-1800      1800-2000      2000-2200      2200-2400      2400-2600      2600-2800      2800-3000      3000-3200      3200-3400      3400-3600      >3600 Map of dietary energy availability per person per day in 2001–2003 (kcal/person/day).[६५]      no data      <1600      1600–1800      1800–2000      2000–2200      2200–2400      2400–2600      2600–2800      2800–3000      3000–3200      3200–3400      3400–3600      >3600
मू पौ: Diet and obesity

The per capita dietary energy supply varies markedly between different regions and countries. It has also changed significantly over time.[६६] From the early 1970s to the late 1990s the average calories available per person per day (the amount of food bought) has increased in all part of the world except Eastern Europe. The United States had the highest availability with 3654 calories per person in 1996.[६७] This increased further in 2002 to 3770.[६८] During the late 1990s Europeans had 3394 calories per person, in the developing areas of Asia there were 2648 calories per person, and in sub-Sahara Africa people had 2176 calories per person.[६७][६९]

USDA chart showing the increase in soda consumption and the decrease in milk consumption from 1947 to 2001.[७०]

The widespread availability of nutritional guidelines[७१] have done little to address the problems of overeating and poor dietary choices.[७२] In the period of 1971–2000, obesity rates in the United States increased from 14.5% to 30.9%.[७३] During the same time period, an increase occurred in the average amount of calories consumed. For women, the average increase was 335 calories per day (1542 calories in 1971 and 1877 calories in 2004), while for men the average increase was 168 calories per day (2450 calories in 1971 and 2618 calories in 2004). Most of these extra calories came from an increase in carbohydrate consumption rather than an increase in fat consumption.[७४] The primary sources of these extra carbohydrates are sweetened beverages, which now accounts for almost 25 percent of daily calories in young adults in America.[७५] Consumption of sweetened drinks is believed to be contributing to the rising rates of obesity.[७६][७७]

A comparison of a cheeseburger 20 years ago (left) which had 333 calories with a modern cheeseburger (right) contains 590 calories.

As societies become increasingly reliant on energy-dense, large portion, fast-food meals, the association between fast food consumption and obesity becomes more concerning.[७८] In the United States consumption of fast food meal has tripled and calorie intake from fast food has quadrupled between 1977 and 1995.[७९]

Agricultural policy and techniques in the United States and Europe have led to lower food prices. In the United States, subsidization of corn, soy, wheat, and rice through the U.S. farm bill has made the main sources of processed food cheap compared to fruits and vegetables.[८०]

There is little evidence to support the commonly expressed view that some obese people eat little yet gain weight due to a slow metabolism. On average obese people have a greater energy expenditure than thin people. This is because it takes more energy to maintain an increased body mass.[४५] Obese people also under report how much food they consume compared to those of normal weight.[९] Tests of human subjects carried out in a calorimeter support this conclusion.[८१]

Sedentary lifestyle

मू पौ: Exercise trends

A sedentary lifestyle plays a significant role in obesity.[९] Worldwide there has been a large shift towards less physically demanding work,[८२][८३][८४]
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