Obesity

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. 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 both an individual clinical condition and is increasingly viewed as a serious public health problem.

Contents [hide]

1 Definition

1.1 BMI

1.2 Waist circumference

1.3 Body fat measurement

1.4 Gestalt

1.5 Risk factors and comorbidities

2 Causes

2.1 Causative factors

2.2 Evolutionary aspects

2.3 Neurobiological mechanisms

2.4 Poverty link

3 Complications

4 Therapy

5 Cultural and social significance

5.1 Etymology

5.2 History and obesity

5.3 Contemporary culture

5.4 Popular culture

6 Public health and policy

6.1 Prevalence

6.2 Environmental factors

6.3 Public health and policy responses

6.4 Non-medical consequences

7 See also

8 References

9 External links

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.[1] 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.[2] It is calculated by dividing the subject's weight in kilograms by the square of his/her height in metres (BMI = kg / m2).

The current definitions commonly in use establish the following values, agreed in 1997 and published in 2000:[3]

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) obese

BMI is a simple and widely used method for estimating body fat.[4] 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.[5]

Waist circumference

BMI 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.[6]

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)[6] 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. 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]

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. In these cases, BMI thresholds provide simple targets all patients can understand.[7]

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.[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.

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