Definitions

Overweight

Overweight

[adj. oh-ver-weyt; n. oh-ver-weyt; v. oh-ver-weyt]

Overweight is generally defined as having more body fat (adipose tissue) than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary. As much as 64% of the United States adult population is considered either overweight or obese, and this percentage has increased over the last four decades. A series of graphics from the Centers for Disease Control and Prevention (CDC) shows the trend in which the prevalence of obesity has increased in the U.S. during the past three decades: Obesity Epidemic: U.S. Temporal Trends 1985-2004 Excess weight has reached epidemic proportions globally, with more than 1 billion adults being either overweight or obese. Increases have been observed across all age groups.

A healthy body requires a minimum amount of fat for the proper functioning of the hormonal, reproductive, and immune systems, as thermal insulation, as shock absorption for sensitive areas, and as energy for future use. But the accumulation of too much storage fat can impair movement and flexibility, and can alter the appearance of the body.

Classification

The degree to which a person is overweight is generally described by Body Mass Index. The range for overweight is a BMI of 25 to 29.9 with BMI's >= 30 classified as obesity. There are however several other common ways to measure the amount of adiposity or fat present in an individual's body.

Body Mass Index, or BMI is a measure of a persons weight taking into account their height. It is given by the formula: BMI equals body weight divided by the square of the persons height; with weight in kilograms and height in meters. BMI numbers however are typically used and written as unitless numbers. BMI provides a significantly more accurate representation of body fat content than simply measuring a persons weight. It is highly correlated with both percentage of body fat and body fat mass. It does not take into account some factors such as pregnancy, bodybuilding, or children which effect body composition however is an accurate reflection of fat percentage in the majority of the adult population.

The weight of the individual is measured and compared to an estimated ideal weight. This is the easiest and most common method, but by far the least accurate, as it only measures one quantity (weight) and often does not take into account many factors such as height, body type, and relative amount of muscle mass.

With this method, the skin at several specific points on the body is pinched and the thickness of the resulting fold is measured. This measures the thickness of the layers of fat located under the skin, from which a general measurement of total amount of fat in the body is calculated. This method can be reasonably accurate for many people, but it does assume particular patterns for fat distribution over the body which may not apply to all individuals, and does not account for fat deposits which may not be directly under the skin. Also, as the measurement and analysis generally involves a high degree of practice and interpretation, for an accurate result it must be performed by a professional and cannot generally be done by patients themselves.

This method involves passing a small electrical current through the body and measuring the body's resistance to the electrical flow. As fat and muscle conduct electricity differently, this method can provide a direct measurement of the percentage of body fat present as compared to muscle mass. In the past, this technique could only be performed reliably by trained professionals with specialized equipment, but it is now possible to buy "home kits" which allow individuals to do this themselves with a minimum of training. Despite the improved simplicity of this process over the years, however, there are a number of factors which can affect the results, including hydration and body temperature, so a fair amount of care must still be taken when applying this test to ensure that the results are in fact accurate and applicable.

Considered one of the more accurate methods of measuring body fat, this technique involves completely submerging the subject underwater and using special equipment to measure his or her weight while submerged. This weight is then compared with "dry weight" as recorded outside the water to determine overall body density. As fat is less dense than muscle, careful application of this technique can provide a reasonably close estimate of fat content in the body. This technique does, however, require expensive specialized equipment and trained professionals to administer it properly.

  • DEXA (dual energy X-ray absorptiometry)

Originally developed to measure bone density, DEXA imaging has also come to be used as a precise way to determine body fat content by using the density of various body tissues to identify which portions of the body are fat. This test is generally considered to be very accurate, but requires a great deal of expensive medical equipment and trained professionals to perform.

The most common method for discussing this subject and the one used primarily by researchers and advisory institutions is body mass index (BMI). Definitions of what is considered to be overweight vary by ethnicity. The current definition proposed by the United States National Institutes of Health (NIH) and the World Health Organization (WHO) designate whites, hispanics and blacks with a BMI of 25 kg/m2 or more as overweight. For Asians, overweight is a BMI between 23 and 29.9 kg/m2 and obesity for all groups is a BMI >30 kg/m2

BMI, however, does not account extremes of muscle mass, some rare genetic factors, the very young, and a few other individual variations. Thus it is possible for an individuals with a BMI of less than 25 to have excess body fat, while others may have a BMI that is significantly higher without falling into this category. Some of the above methods for determining body fat are more accurate then BMI but come with added complexity.

If an individual is overweight and has excess body fat it could cause health risks.

Health-related implications

While the negative health outcomes associated with obesity are accepted within the medical community, the health implications of the overweight category are more controversial. The generally accepted view is that being overweight causes similar health problems as obesity just to a lesser degree. Adams et al. estimated that the risk of death increases by 20 to 40 percent among overweight persons. and the Framingham Heart Study found that being overweight at age 40yrs reduced your life expectancy by three years.

Flegal et al., however, found that the mortality rate for individuals who are classified as overweight (BMI 25 to 30) may actually be lower than for those with an "ideal" weight (BMI 18.5 to 25).

Being overweight has been identified as a cause of cancer, and is projected to overtake smoking as the primary cause of cancer in developed countries as cases of cancer linked to smoking dwindle.

Psychological well-being is also at risk in the overweight individual. Discrimination against fat persons is common socially and legally. This may affect their ability to find a mate or employment.

Causes

Being overweight is generally caused by the intake of more calories (by eating) than are expended by the body (by exercise and everyday living). Factors which may contribute to this imbalance include:

Noncauses

Treatment

A large number of people undergo some form of treatment to attempt to reduce their weight, usually either in an attempt to improve their health, to improve their lifestyle, or for cosmetic reasons. The generally recommended treatment for being overweight is a modified or controlled diet in conjunction with increased physical exercise. For those who are obese rather than overweight, more intensive therapies such as anti-obesity drugs and/or bariatric surgery are sometimes used.

Studies suggest that reducing calorie intake by itself (dieting) may have short-term effects but does not lead to long-term weight loss, and can often result in gaining back all of the lost weight and more in the longer term. For this reason, it is generally recommended that weight-loss diets not be attempted on their own but instead in combination with increased exercise and long-term planning and weight management.

The health benefits of weight loss are also somewhat unclear. While it is generally accepted that for significantly obese patients, losing weight can reduce health risks and improve quality of life, there is some evidence to suggest that for merely overweight patients, the health effects of attempting to lose weight may actually be more detrimental than simply remaining overweight. Moreover, for all individuals, repeatedly losing weight and then gaining it back (weight cycling or "yo-yo dieting"), is believed to do more harm than good and can be the cause of significant additional health problems. This is caused by the loss of more muscle than fat.

There is no healthy, short-term solution for solving obesity, or being overweight. Changes in lifestyle, such as more exercise or dieting, must be permanent changes.

See also

References

External links

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