Classification of obesity - AbsoluteAstronomy.com

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...

is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health. Relative weight and body mass index (BMI)

Body mass index

The body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...

are nearly identical and are reasonable estimates of body fatness as measured by percentage body fat

Body fat percentage

A person's body mass percentage is the total weight of the person's fat divided by the person's weight and consists of essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than...

. However, BMI does not account for the wide variation in body fat distribution, and may not correspond to the same degree of fatness or associated health risk in different individuals and populations. Other measurements of fat distribution include the waist–hip ratio and body fat percentage

Body fat percentage

. Normal weight obesity is a condition of having normal body weight, but high body fat percentages with the same health risks of obesity.

BMI

Body mass index or BMI is a simple and widely used method for estimating body fat mass. BMI was developed in the 19th century by the Belgian

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

statistician and anthropometrist

Anthropometry

Anthropometry refers to the measurement of the human individual...

Adolphe Quetelet

Lambert Adolphe Jacques Quetelet was a Belgian astronomer, mathematician, statistician and sociologist. He founded and directed the Brussels Observatory and was influential in introducing statistical methods to the social sciences...

. BMI is an accurate reflection of body fat percentage in the majority of the adult population. It however is less accurate in people such as body builders

Bodybuilding

Bodybuilding is a form of body modification involving intensive muscle hypertrophy. An individual who engages in this activity is referred to as a bodybuilder. In competitive and professional bodybuilding, bodybuilders display their physiques to a panel of judges, who assign points based on their...

and pregnant women. A formula combining BMI, age and gender can be used to estimate a person's body fat percentage to an accuracy of 4%. An alternative method, body volume index

Body volume index

The Body Volume Index is a new measurement for human obesity that has been proposed as an alternative to the Body Mass Index .BMI is based on a measurement of total mass, irrespective of the location of the mass, but BVI looks at the relationship between mass and volume distribution...

(BVI), is being developed in an effort to better take into account different body shapes.

BMI	Classification
< 18.5	underweight
18.5–24.9	normal weight
25.0–29.9	overweight
30.0–34.9	class I obesity
35.0–39.9	class II obesity
≥ 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

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

or US "Customary" units:

Metric:

US/Customary and imperial:

where

is the subject's weight in pounds and

is the subject's height in inches.

The most commonly used definitions, established by the World Health Organization

World Health Organization

The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

(WHO) in 1997 and published in 2000, provide the values listed in the table at right.

Some modifications to the WHO definitions have been made by particular bodies. The surgical literature breaks down class III obesity into further categories, though the 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 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 while China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

uses a BMI of greater than 28.

Waist circumference and waist–hip ratio

In the United States a waist circumference of >102 cm in men and >88 cm in women or 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 used to define central obesity.

In the European Union waist circumference of ≥ 94 cm in men and ≥ 80 cm in non pregnant women are used as cut offs for central obesity.

A lower cut off of 90 cm has been recommended for South Asian and Chinese men, while a cut off of 85 cm has been recommended for Japanese men.

In those with a BMI under 35, intra-abdominal body fat is related to negative health outcomes independent of total body fat. Intra-abdominal or visceral fat has a particularly strong correlation with cardiovascular disease

Cardiovascular disease

Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...

. In a study of 15,000 people, waist circumference also correlated better with metabolic syndrome

Metabolic syndrome

Metabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...

than BMI. Women with abdominal obesity have a cardiovascular risk similar to that of men. 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.

Body fat percentage

Body fat percentage is total body fat expressed as a percentage of total body weight. There is no generally accepted definition of obesity based on total body fat. Most researchers have used >25% in men, and >30% in women, as cut-points to define obesity. However, the finding that metabolic disturbance increases with increasing body fat percentage suggests that focusing exclusively on cut-points of body fat percent may be of limited value.

Body fat percentage can be estimated from a person's BMI by the following formula:

where gender is 0 if female and 1 if male

This formula takes into account the fact that body fat percentage tends to be 10 percentage point

Percentage point

Percentage points are the unit for the arithmetic difference of two percentages.Consider the following hypothetical example: in 1980, 40 percent of the population smoked, and in 1990 only 30 percent smoked...

s greater in women than in men for a given BMI. It recognizes that a person's percentage body fat tends to increase as they age, even if their weight and BMI remain constant. The results of this formula have been shown to have an accuracy of 4% in one group of individuals.

There are many other methods used to determine body fat percentage. Hydrostatic weighing

Hydrostatic weighing

Hydrostatic weighing is a method for measuring the mass density of a body.-Method:The following method has the advantage of needing no volume information of the body...

, one of the most accurate methods of body fat calculation, involves weighting a person underwater. Two other simpler and less accurate methods have been used historically but are now not recommended. The first is the skinfold test, in which a pinch

Pinch (action)

A pinch is a grip of a flexible object in which a portion is taken between two fingers, until it hurts, or something of resemblance and squeezed so the gripped portion of the object is lifted from its normal level...

of skin is precisely measured to determine the thickness of the subcutaneous fat layer. The other is bioelectrical impedance analysis

Bioelectrical impedance analysis

Bioelectrical impedance analysis is a commonly used method for estimating body composition. Since the advent of the first commercially available devices in the mid-1980s the method has become popular owing to its ease of use, portability of the equipment and its relatively low cost compared to...

which uses electrical resistance. Bioelectrical impedance has not been shown to provide an advantage over BMI.

Body fat percentage measurement techniques used mainly for research include computed tomography

Computed tomography

X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

(CT scan), magnetic resonance imaging

Magnetic resonance imaging

Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

(MRI), and dual energy X-ray absorptiometry

Dual energy X-ray absorptiometry

Dual-emission X-ray absorptiometry is a means of measuring bone mineral density . Two X-ray beams with differing energy levels are aimed at the patient's bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone...

(DEXA). These techniques provide very accurate measurements, but it can be difficult to obtain in the severely obese due to weight limits of most equipment and insufficient diameter of many CT or MRI scanners.

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

Percentile

In statistics, a percentile is the value of a variable below which a certain percent of observations fall. For example, the 20th percentile is the value below which 20 percent of the observations may be found...

. 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.

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.

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. Activities from self propelled transport, to school physical education, and organized sports has been declining in many countries.

Because childhood obesity often persists into adulthood, and is associated with numerous chronic illnesses, it is important that children who are obese be tested for hypertension

Hypertension

Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

, diabetes, hyperlipidemia

Hyperlipidemia

Hyperlipidemia, hyperlipoproteinemia, or hyperlipidaemia is the condition of abnormally elevated levels of any or all lipids and/or lipoproteins in the blood...

, and fatty liver

Fatty liver

Fatty liver, also known as fatty liver disease , is a reversible condition where large vacuoles of triglyceride fat accumulate in liver cells via the process of steatosis...

.

Treatments used in children are primarily lifestyle interventions and behavioral techniques. Medications are not FDA approved for use in this age group.

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