Overweight

This article is about the medical term. For the stock market term, see overweight (stock market).

The term overweight means that a person has 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 overweight, and this percentage is increasing.Katherine M. Flegal, PhD; Margaret D. Carroll, MS; Cynthia L. Ogden, PhD; Clifford L. Johnson, MSPH (2002). "Prevalence and Trends in Obesity Among US Adults, 1999-2000". JAMA 288 (14): 1723–1727. PMID 12365955. . 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 two decades: Obesity Epidemic: U.S. Temporal Trends 1985-2004

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 overweight is generally described using an indication of the amount of excess body fat present. There are several common ways to measure the amount of fat present in an individual\'s body.(See also body fat percentage):

• Simple Weighing: 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.
• Body Mass Index (BMI): This is an adaptation of simple weighing which attempts to take into account the subject\'s general body size by dividing the weight by the height squared (the units for BMI are kg/m², but are rarely referenced, and BMI numbers are typically written and used as unitless numbers). This provides a slightly more accurate representation than simply measuring raw weight, but still ignores many factors which can affect the results, and is generally not accurate for many individuals.
• Skinfold Calipers or "pinch test": 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.
• Bioelectrical impedance analysis: 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.
• Hydrostatic Weighing: 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.

Despite the inherent inaccuracies, the most common method for discussing this subject used by researchers and advisory institutions is body mass index (BMI) numbers. Definitions of what is considered to be overweight change from time to time and sometimes from country to country, but the current definition proposed by both the United States National Institutes of Health (NIH) and the World Health Organization (WHO) designate anyone with a BMI of 25 kg/m² or more to be overweight.

BMI, however, does not account for differing amounts of muscle mass, genetic factors, or many other individual variations, and thus many individuals can have a BMI of less than 25 and still be considered overweight, while others may have a BMI that is significantly higher without falling into this categoryDympna Gallagher, Steven B Heymsfield, Moonseong Heo, Susan A Jebb, Peter R Murgatroyd and Yoichi Sakamoto (2000). "Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index". AJCN 72 (3): 694–701. PMID 10966886. .. Many of the more accurate methods mentioned above for determining body fat content can provide better indications of whether a particular individual is overweight or not.

If an individual is sufficiently overweight that excess body fat could present substantial health risks, he or she is considered to be obese. It is possible for someone to be overweight without being obese (according to the NIH and WHO, a BMI between 25 and 30 is considered to be "overweight" but not "obese"). Again, the designation of "obesity" is subject to a great deal of interpretation and many individual factors, so an individual with a BMI well below 30 may be considered to be obese depending on their particular condition, while in some cases a BMI above 30 may not actually indicate obesity (although likely still does indicate being overweight).

Health-related implications

Animals can suffer from obesity as well. This German Shepherd dog is noticeably overweight.

While the health issues associated with obesity are well accepted within the medical community, the health implications of the overweight category are more controversial. The generally accepted view has been that overweight often shares adverse risks with obesity, relative to normal weight. Adams et al. estimated that risk of death increases by 20 to 40 percent among overweight persons.Kenneth F. Adams, Ph.D., Arthur Schatzkin, M.D., Tamara B. Harris, M.D., Victor Kipnis, Ph.D., Traci Mouw, M.P.H., Rachel Ballard-Barbash, M.D., Albert Hollenbeck, Ph.D., and Michael F. Leitzmann, M.D. (2006). "Overweight, Obesity, and Mortality in a Large Prospective Cohort of Persons 50 to 71 Years Old". NEJM 355 (8): 763–788. 

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)Katherine M. Flegal, PhD; Barry I. Graubard, PhD; David F. Williamson, PhD; Mitchell H. Gail, MD, PhD (2005). "Excess Deaths Associated With Underweight, Overweight, and Obesity". JAMA 293 (15): 1861–1867. PMID 15840860. .http://www.nytimes.com/2007/11/07/health/07fat.html?_r=2&oref=slogin&adxnnlx=1194438040-WQ8KzBIizxq%20luYBavokrw&pagewanted=print.

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.http://www.livescience.com/health/080219-bad-fat.html

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. The receipt of overt remarks from childhood into old age also shape the personality of the overweight individual, either making him/her more resolute and obstinate or too willing to please others.^{[citation needed]}

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:

• Limited physical exercise and sedentary lifestyle
• Overeating
• Poor nutrition
• Genetic predisposition
• Hormonal imbalances (e.g. hypothyroidism)
• Metabolic disorders, which could be caused by repeated attempts to lose weight by weight cycling,
• Eating disorders (such as binge eating)
• Alcoholism
• Stress
• Insufficient or poor-quality sleep
• Psychotropic medication
• Smoking cessation and other stimulant withdrawal

The amount of body fat is regulated to some extent subconsciously by the brain (by controlling caloric intake through appetite and food preference). Although the exact mechanisms by which this occurs are not entirely known, one common theory suggests that each person may possess an inherent "set point" weight which the brain attempts to maintain, and that this set point may vary for each individual depending on a variety of factors including genetic predisposition, environment, and past experience.

This leads to the conclusion that some individuals may be predisposed to naturally maintaining different body weights than others, and thus it may be easier for some people to avoid being overweight, while others may find it much more difficult. It also suggests, however, that an individual\'s set point may be changeable with appropriate environment and conditioning.

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 (see Obesity).

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 overweightSørensen TI, Rissanen A, Korkeila M, Kaprio J. (2005). "Intention to Lose Weight, Weight Changes, and 18-y Mortality in Overweight Individuals without Co-Morbidities.". PLoS 2 (6): e171. PMID 15971946. .. 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

• Big Beautiful Women
• Body image
• Physical attractiveness
• Underweight

References

External links

• Obesity Epidemic: U.S. Temporal Trends 1985-2004
• Ranking of Most Overweight Countries in the World 2005
• World Health Organization fact sheet on obesity and overweight

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