In adults, besity is typically defined by body mass index (BMI) and further evaluated in terms of fat distribution via the waist–hip ratio and total cardiovascular risk factors. BMI is closely related to both percentage body fat and total body fat.
In children, because a healthy weight varies with both age and sex, obesity is deifined not as an absolute number, but in relation to a historical normal group. As a result, obesity is a BMI greater than the 95th percentile. The reference data on which these percentiles were based date from 1963 to 1994, and thus have not been affected by the recent increases in weight across the population.
BMI itself is calculated by dividing the subject's mass by the square of his or her height, typically expressed either in metric or US 'customary' or imperial units.
The equations for BMI are thus:
Metric: BMI = kilograms / meters2
US customary and imperial: BMI = lb * 703 / in2
(lb being the weight in pounds and in being the height in inches)
Using the BMI measurement for adults, the definitions for weight class, as defined by the World Health Organization and published in 2000 are given in the table below:
| BMI Women | BMI Men | Classification |
|---|---|---|
| < 19.1 | < 20.7 | underweight |
| 19.1-25.8 | 20.7-26.4 | normal weight |
| 25.8-27.3 | 26.4-27.8 | marginally overweight |
| 27.3–32.3 | 27.8–31.1 | overweight |
| 32.3–34.9 | 31.1–34.9 | class I obesity |
| 35.0–39.9 | 35.0–39.9 | class II obesity |
| ≥ 40.0 | ≥ 40.0 | class III obesity |
The most quoted definition of Overweight for adults (a BMI of 25 kg/M2 was actually chosen to be suitable for international standardization and to be simple enough to remember and to calculate with a pencil and paper. As the table above shows, the real situation is more complex.
Some modifications to the WHO definitions have been made by particular bodies. The surgical literature breaks down "class III" obesity into further categories whose exact values are still disputed.
Any BMI ≥ 35 or 40 is severe obesity
A BMI of ≥ 35 or 40–44.9 or 49.9 is morbid obesity
A BMI of ≥ 45 or 50 is super obesity
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 while China uses a BMI of greater than 28.
The problems with BMI (a muscular person with normal body fat content may have an elevated BMI due to their increased muscle mass), and the variation between populations has led to a seciond measurement, the ratio of the circumference of the belly to that of the hips (ie measure around the belly then measure around the hips; divide the first number by the second to get the ratio).
If you’re a woman, the waist-to-hip ratio should come out as no more than 0.8. Form men, a healthy waist-to-hip ratio for is 0.95.
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Current measurements indicate that obesity is one of the leading preventable causes of death world-wide. American and European studies have shown that overall mortality risk is lowest with a BMI of between 20 and 25 kg/m2 in non-smokers and 24 to 27 kg/m2 in current smokers. A BMI above 32 has been associated with a doubled mortality rate among women over a 16-year period. On average, obesity reduces life expectancy by between six and seven years and a BMI of between 30 and 35 reduces life expectancy by two to four years. In cases of severe obesity (BMI greater than 40), life expectancy is reduced by 10 years. MorbidityObesity increases the risk of many mental and mental conditions. Most commonly these are associated metabolic disorders, such as diabetes mellitus type 2, high blood pressure, high blood cholesterol, and high triglyceride levels. Other diseases attributed to the effects of increased fat mass in the body include osteoarthritis, obstructive sleep apnea, social stigmatization. Diseases associated with an increased number of fat cells include diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease. Increases in body fat alter the body's response to insulin, potentially leading to insulin resistance. Increased fat also creates a proinflammatory state, and a prothrombotic state.
PathophysiologyThere are a number of pathophysiological effects involved in the development and maintenance of obesity. In 1994 a chemical, leptin was discovered, this is a hormone that controls appetite through its action on the central nervous system. In particular, it and other appetite-related hormones act on the hypothalamus, a region of the brain central to the regulation of food intake and energy expenditure. There are several circuits within the hypothalamus that contribute to its role in integrating appetite, the melanocortin pathway being the most well understood. The interesting thing is that deficiency in leptin signaling, either via leptin deficiency or leptin resistance, leads to overfeeding and may account for some genetic and acquired forms of obesity. Causes of ObesityCausesMost cases of obesity can be explained by a combination of excessive carlorific intake (eating too much) and lack of physical activity. Though the trend in society for increased levels of obesity can be put down to a diet rich in fats and sugars, increased reliance on mechanized transport and a more sedentary work environment. However, some recent reviews also point to ten other contributing factors for obesity, which are: (1) insufficient sleep It should be noted, however, that these are only contributing factors towards obesity and not the main underlying causes, which are still diet and exercise. |
Typical reccomendations for calorific intake to maintain a stable weight is 2500 caloreis per day for men and 2000 calories per day for women. Of course, these are general guidelines only and the exact value will depend on age, levels of physical exertion, external temperature and other factors. For example, a manual labourer working in the arctic might need 5500 caloreis per day.
A calorie is a measure of how much energy your food contains. In fact, the dietary energy supply of a 'typical' meal varies considerably between different regions of the globe and different countries. It also changes over time. For example, from the early 1970s to the late 1990s the average calories available per person per day (the amount of food bought) increased in all parts of the world except Eastern Europe.
As might be expected, the United States had the highest availability with 3,654 calories per person in 1996, which increased further to 3,754 in 2003. During the late 1990s Europeans had 3,394 calories per person, in the developing areas of Asia there were 2,648 calories per person, and in sub-Saharan Africa people had 2,176 calories per person.
If you consume more calories than the body requires to maintain itself on a daily basis, then the excess calories are stored as fat. As food becomes both richer in terms of its fat and sugar content and becomes cheaper (making larger portions an option) then the population as a whole tends to become fatter. There is also a tendency in obese people to consistently under-report their actual food consumption as compared with people of normal weight.
The other main cause of obesity is a lack of exercise (the so-called 'sedentary lifestyle'). Daily work has become less manual and physically demanding (this is a world-wide trend) and currently it is estimated that 60% of the world's population gets insufficient exercise.
There is also a tendency for leisure time to be spend on sedentary activities. In both children and adults, there is an association between television viewing time and the risk of obesity.
Like the majority of human medical conditions, obesity is a result of a combination of genetic and environmental factors. Changes in the various genes controlling appetite and metabolism can pre-dispose a person to obesity when there is suffiecient energy-rich food available. A number of these genes have now been discovered. A good example being the FTP (fat mass and obesity associated gene). When two copies of this gene are present in the genome, the person carrying this variation ahs been found, on average, to be 3–4kg heavier and to have a 1.67-fold greater risk of obesity compared to those without the risk allele.
Obesity is a major feature in several syndromes, such as Prader-Willi syndrome, Bardet-Biedl syndrome, Cohen syndrome, and MOMO syndrome. (The term "non-syndromic obesity" is sometimes used to exclude these conditions.)
Part of the problem is that people, typically, crave fat-rich and sugar-rich foods. The brain is pre-programmed to find such foods pleasurable, possibly as a result of the scarcity of fats and sugars in early humans' diets.
It is known that certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase the risk of obesity. Some of these are the genetic disorders, mentioned above. There are also some congenital or acquired conditions: hypothyroidism, Cushing's syndrome, growth hormone deficiency as well as the eating disorders binge eating disorder and night eating syndrome.
Though obesity is not itself defined as a psychiatric disorder, it can be a symptom. Indeed, the risk of being overweight or obese is much higher in patients with psychiatric disorders than in those without such disorders.
Certain medications are also known to be associated with weight gain. These include: insulin, sulfonylureas, thiazolidinediones, atypical antipsychotics, antidepressants, steroids, certain anticonvulsants (phenytoin and valproate), pizotifen, and some forms of hormonal contraception.
There can be little doubt that environmental and peer-group factors affect both the levels of obesity and its perceoption (which is why a society as a whole can become more obese).
Though there is a correlation between social class and BMI, the precise effect varies globally. In developed countries, women of a high social class were less likely to be obese. No significant differences were seen among men of different social classes. In the developing world, women, men, and children from high social classes had greater rates of obesity. Among developed countries, levels of adult obesity, and percentage of teenage children who are overweight, are correlated with income inequality. A similar relationship is seen among US states: more adults, even in higher social classes, are obese in more unequal states.
Smoking has a significant effect on an individual's weight. Those who quit smoking gain an average of 4.4 kilograms for men and 5.0 kilograms for women over ten years. However, changing rates of smoking have had little effect on the overall rates of obesity.
In the United States the number of children a person has is related to their risk of obesity. A woman's risk increases by 7% per child, while a man's risk increases by 4% per child. This could be partly explained by the fact that having dependent children decreases physical activity in Western parents.
In the developing world urbanization is playing a role in increasing rate of obesity. In China overall rates of obesity are below 5%; however, in some cities rates of obesity are greater than 20%.
Malnutrition in early life is believed to play a role in the rising rates of obesity in the developing world.[120] Endocrine changes that occur during periods of malnutrition may promote the storage of fat once more food energy becomes available.
Just as over-eating and lack of excersise are the main causes of obesity, the main treatment consists of dieting (restricting calorific intake) and physical exercise (being more active).
Diet programs tend to produce weight loss over the short term, but if this is not associated with increased physical activity, that weight loss is frequently diffiecult to maintain over the long-term.
There is one madicine orlistat (Xenical), that is current widely available and approved for long term use. Weight loss however is modest with an average of 2.9 kg at 1 to 4 years and there is little information on how these drugs affect longer-term complications of obesity.
By far the most effective treatment for obesity is bariatric surgery. Surgery for severe obesity is associated with long-term weight loss and decreased overall mortality. One study found a weight loss of between 14% and 25% (depending on the type of procedure performed) at 10 years, and a 29% reduction in all cause mortality when compared to standard weight loss measures. However, due to its cost and the risk of complications, researchers are searching for other effective yet less invasive treatments.
The truth is that before the 20th century, obesity was exceedingly rare, but in 1997 the WHO formally recognized obesity as a global health epidemic. As of 2005 the WHO estimates that at least 400 million adults (9.8%) are obese, with higher rates among women than men. The rate of obesity also increases with age at least up to 50 or 60 years old and severe obesity in the United States, Australia, and Canada is increasing faster than the overall rate of obesity
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