Obesity is a medical condition in which excess body fat has
accumulated to the extent that it may have a negative effect on health. People
are generally considered obese when their body mass index (BMI), a measurement
obtained by dividing a person's weight by the square of the person's height, is
over 30 kg/m2, with the range 25–30 kg/m2 defined as overweight. Some East
Asian countries use lower values. Obesity increases the likelihood of various
diseases and conditions, particularly cardiovascular diseases, type 2 diabetes,
obstructive sleep apnea, certain types of cancer, osteoarthritis and
depression.
Obesity is most commonly caused by a combination of
excessive food intake, lack of physical activity, and genetic susceptibility. A
few cases are caused primarily by genes, endocrine disorders, medications, or
mental disorder. The view that obese people eat little yet gain weight due to a
slow metabolism is not generally supported. On average, obese people have a
greater energy expenditure than their normal counterparts due to the energy
required to maintain an increased body mass.
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Obesity is mostly preventable through a combination of
social changes and personal choices. Changes to diet and exercising are the
main treatments. Diet quality can be improved by reducing the consumption of
energy-dense foods, such as those high in fat or sugars, and by increasing the
intake of dietary fibre. Medications can be used, along with a suitable diet,
to reduce appetite or decrease fat absorption. If diet, exercise, and medication
are not effective, a gastric balloon or surgery may be performed to reduce
stomach volume or length of the intestines, leading to feeling full earlier or
a reduced ability to absorb nutrients from food.
Obesity is a leading preventable cause of death worldwide,
with increasing rates in adults and children. In 2015, 600 million adults (12%)
and 100 million children were obese in 195 countries. Obesity is more common in
women than men. Authorities view it as one of the most serious public health problems
of the 21st century. Obesity is stigmatized in much of the modern world
(particularly in the Western world), though it was seen as a symbol of wealth
and fertility at other times in history and still is in some parts of the
world. In 2013, the American Medical Association classified obesity as a
disease.
CLASSIFICATION
Obesity is a medical condition in which excess body fat has
accumulated to the extent that it may have an adverse effect on health. It is
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,
a healthy weight varies with age and sex. Obesity in children and adolescents
is defined not as an absolute number but in relation to a historical normal
group, such that 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. BMI is
defined as the subject's weight divided by the square of their height.
BMI is usually expressed in kilograms per square metre,
resulting when weight is measured in kilograms and height in metres. To convert
from pounds per square inch multiply by 703 (kg/m2)/ (lb/sq. in).
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EFFECTS ON HEALTH
Excessive body weight is associated with various diseases
and conditions, particularly cardiovascular diseases, diabetes mellitus type 2,
obstructive sleep apnea, certain types of cancer, osteoarthritis and asthma. As
a result, obesity has been found to reduce life expectancy.
Mortality
Relative risk of death over 10 years for white men and women
who have never smoked in the United States by BMI.
Obesity is one of the leading preventable causes of death
worldwide. A number of reviews have found that mortality risk is lowest at a
BMI of 20–25 kg/m2 in non-smokers and at 24–27 kg/m2 in current smokers, with
risk increasing along with changes in either direction. This appears to apply
in at least four continents. In contrast, a 2013 review found that grade 1
obesity (BMI 30–35) was not associated with higher mortality than normal
weight, and that overweight (BMI 25–30) was associated with "lower"
mortality than was normal weight (BMI 18.5–25). Other evidence suggests that
the association of BMI and waist circumference with mortality is U- or
J-shaped, while the association between waist-to-hip ratio and waist-to-height
ratio with mortality is more positive. In Asians the risk of negative health
effects begins to increase between 22–25 kg/m2. A BMI above 32 kg/m2 has been
associated with a doubled mortality rate among women over a 16-year period. In
the United States, obesity is estimated to cause 111,909 to 365,000 deaths per
year, while 1 million (7.7%) of deaths in Europe are attributed to excess
weight. On average, obesity reduces life expectancy by six to seven years, a
BMI of 30–35 kg/m2 reduces life expectancy by two to four years, while severe
obesity (BMI > 40 kg/m2) reduces life expectancy by ten years.
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Morbidity
Obesity increases the risk of many physical and mental
conditions. These comorbidities are most commonly shown in metabolic syndrome,
a combination of medical disorders which includes: diabetes mellitus type 2,
high blood pressure, high blood cholesterol, and high triglyceride levels.
Complications are either directly caused by obesity or
indirectly related through mechanisms sharing a common cause such as a 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 underlies 64% of cases of diabetes in men and 77% of
cases in women.
Health consequences fall into two broad categories: those
attributable to the effects of increased fat mass (such as osteoarthritis,
obstructive sleep apnea, social stigmatization) and those due to the increased
number of fat cells (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.
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