ASSESSMENT OF OBESITY AND HEALTH RISKS

Obesity is the accumulation of excess adipose tissue within the body. he degree of adiposity and the distribution of body fat have been consistently correlated with relative risk of adverse health. Originating in the early 20th century with the Metropolitan Insurance Company weight and height-for-weight tables, assessment techniques now include a variety of methodologies that involve varying levels of accuracy in estimation and measurement of adiposity and body composition. Choosing how to measure adiposity and associated health risk depends on the setting and purpose of the assessment.

MEASUREMENT METHODS

Sophisticated adiposity assessment methodologies are generally used in research rather than large-scale screening. Technologies such as dual energy X-ray absorptiometry (DEXA), computerized tomography (CT) scanning, and air displacement-plethysmography (Bod Pod) all ofer a high level of accuracy but are expensive and time consuming. Others methods, including underwater weighting and stable isotope dilution measurement, although safe, are invasive and inconvenient in clinical settings. Bioelectrical impedance analysis and the measurement of body dimensions, such as arm circumference and subscapular skin fold thickness, estimate body fatness and are easy to perform, but lack reliability and are inaccurate with obese persons making them less than optimal for measuring obesity across populations.

BODY MASS INDEX (BMI)

Determined by the indirect calculation of weight in kilograms to the square of height in meters (kg/m2), BMI is a simple and convenient proxy measure for excess adiposity in clinical settings. Many health-related indices, such as mortality risk, heart disease, high blood pressure, and diabetes, have a graded and continuous correlation with BMI. BMI is highly correlated with the precise DEXA method of fat assessment and is thus the universal acceptance as the standard index for the deinition of overweight and obesity. hree methods are used to determine BMI: the calculation of the individual’s weight divided by the height in meters squared, the use of several Web-based computation sites, or comparison with published reference tables that plot BMI as height and weight intersect. In adults, regardless of sex or age, one set of BMI values is used to assess adiposity and health risk. Based on classiication by the National Heart Lung and Blood Institute of the National Institutes of Health (NIH), a BMI under 25 is normal, 25–29.9 is overweight, and a BMI of 30 and above is obese.

BMI is particularly useful for large population surveys and for screening purposes; however, it may not always categorize individual risk well. Although BMI represents the degree of body fat, it does not distinguish between excess weight due to fat mass and nonfat mass such as muscle, edema, or bone. For example body builders have a low percentage of body fat, but their BMI may be in the overweight range because of their large lean muscle mass. Individuals with higher fat mass may be classiied as normal BMI despite having a low bone density or muscle mass. Another limitation of BMI is that the relationship to body fatness for those of diferent gender, age, and ethnicity has not been irmly established. In a family study of 665 African American and Caucasian men and women over the age of 17, the relationship of BMI and fat mass was dependent on gender and age, particularly at lower BMI levels. For women, race was also a factor.

BMI USE IN CHILDREN

For children and adolescents, there is controversy regarding the deinition of normal BMI values due to concerns about possible interference with normal growth, self-esteem, and the desire to promote the development of healthy food behaviors and habits. During childhood, BMI changes with growth and development.

There are several periods in which sex, growth, and maturation patterns afect muscular gains and account for BMI variation, rather than adiposity. hus, several authorities have developed child BMI levels including the International Obesity Task Force, the British Child Growth Foundation, and the U.S. Centers for Disease Control and Prevention (CDC). In the United States, the CDC charts are based primarily on data collected during national health examination surveys conducted by the National Center for Health Statistics between 1963 and 1994, and as such, are not skewed by recent increases in the prevalence of overweight children. A BMI equal or greater than CDC’s 95th percentile for age and gender has a sensitivity of 49 percent and specificity of 90 percent in identifying children with three or more risk factors for cardiovascular disease.

Excess adiposity in children is known to produce a number of comorbidities in childhood as well as increasing the risk for obesity in adulthood. hus, the American Academy of Pediatrics and U. S. Preventive Services Task Force (USPSTF) recommend annual screening with the BMI growth charts for children between 24 months and 19 years of age. As in adults, the criterion-referenced BMI scale for children does not quantify body composition variations that occur with race and/or ethnicity.

HEALTH RISKS AND BMI MEASUREMENT

he use of BMI is an accepted method of classifying a patient’s risk of the mortality and morbidity due to numerous chronic diseases associated with obesity, including hypertension, hypercholesterolemia, and Type 2 diabetes mellitus (T2DM). hese conditions are known to predispose individuals to cardiovascular disease and stroke and may further increase the risk of subsequent mortality. Numerous health risks that are not usually life threatening are also known to be linked to obesity, including sleep apnea, osteoarthritis, gall bladder disease, gastroesophageal relux disease, respiratory problems, and depression. In women, obesity is associated with higher levels of pregnancy complications, menstrual irregularities, stress incontinence, and hirsutism (hair growth in places where it is usually minimal or nonexistent). Breast, endometrial, prostate, and colon cancer have also been found to occur more frequently in obese individuals. For all complications, the risk is graded beginning at a BMI level of 20 and rises more steeply as BMI increases.

ABDOMINAL FAT

he distribution of body fat has significant health implications. Abdominal, particularly visceral, fat as compared to subcutaneous or retroperitoneal abdominal fat is associated with higher risk of metabolic syndrome and T2DM. Abdominal obesity, as measured by waist circumference (WC), is known to be a better predictor of health risk among those of normal weight, overweight, and obese categories than percent fat measured by DEXA or BMI. Waist circumferences >102 centimeters or >40 inches in men and >88 centimeters or >35 inches in women are associated with increased risks for T2DM, dyslipidemia, hypertension, and cardiovascular disease. CT and MRI can accurately measure the amount of visceral fat, but these methods are too expensive for routine use.

Waist circumference coupled with BMI is a better predictor of health risk than BMI alone, except for individuals with BMIs ≥35. In these individuals, the WC provides no additional predictive power as WC is likely to measure above the recommended cutoff. In those with a BMI between 25–34.9, WC is important for assessing obesity disease risk. Monitoring for changes over time provides a reference to risk increase or improvement. In older persons, who are likely to have more fat in relationship to muscle mass, measurement of WC should be considered even for those of normal weight. In addition to the gender and age differences, ethnic diferences are seen in abdominal fat and WC associations with disease risk; in particular, Asian Americans or those of Asian descent living outside Asia have increased risk at levels below the recommended cutoffs.

In children and adolescents, there are no published WC parameters for assessment of health risk. Assessing WC has potential for identifying health risk in this population and standards are likely to be developed. In 9- to 11.5-year-old boys and girls, signiicant correlations with WC and fasting insulin, high-density lipoprotein cholesterol (HDL-C), total triglyceride (TG), and C-reactive protein (CRP) have been found.

ASSESSING FOR HEALTH COMPLICATIONS OF OBESITY

he routine screening guidelines recommendations for obese persons include annual fasting lipid panel, which includes a total, low-density lipoprotein (LDL), HDLC, and triglyceride levels along with a blood glucose (fasting or random), and blood pressure measurement. Measurement of blood pressure in obese persons presents a special challenge because of the need for adult large (15 centimeters) or thigh (18 centimeters) sized cufs. Should a cuf too small be used, the patient may be inappropriately diagnosed with hypertension. The correctly sized bladder cuf will cover 40 to 50 percent of upper arm and it one to one-and-a-half times around the circumference of the arm. If there is doubt as to the appropriate size of cuf, arm circumference should be determined. Typically, an arm circumference of 23 to 33 centimeters warrants an adult cuf; 33.1 to 40 centimeters warrants an adult large cuf; and 40.1 to 50 centimeters warrants a thigh cuff.

Health conditions associated with obesity typically rise with increasing levels of obesity. Obese persons are at higher risk for numerous conditions such as asthma, nonalcoholic fatty liver disease, gout, hernias, varicose veins, thrombophlebitis, lymphedema, infertility, depression, social stigmatization, and low self-esteem. he extensive list of potential problems suggests that routine laboratory or diagnostic test assessment might not reveal the associated health complications. Instead, a thorough health history and physical exam should be employed so as to identify areas needing further diagnostic testing and treatment.

BIBLIOGRAPHY. 

M. Krekoukia, et al., “Elevated Total and Central Adiposity and Low Physical Activity Are Associated with Insulin Resistance in Children,” Metabolism (v.56/2, 2007); R. F. Kushner and J. L. Roth, “Medical Evaluation of the Obese Individual,” he Psychiatric Clinics of North America (v.28/1, 2005); A. Must, et al., “he Disease Burden Associated with Overweight and Obesity,” Journal of the American Medical Association (v.282/16, 1999); World Health Organization, “Obesity: Preventing and Managing the Global Epidemic,” paper presented at the World Health Organization, June 3–5, 1997, Geneva, Switzerland.


By Geraldine Budd, Kathleen Falkenstein (Drexel University) in "Encyclopedia of Obesity", Kathleen Keller (General Editor), Sage Publications, California, USA, 2008, excerpts p.58-60. Adapted and illustrated to be posted by Leopoldo Costa.