2003/03/01 by Susan B Racette, Susan B. Racette, Susan S Deusinger +2 · 1 citation
Medicine · #Obesity, Physical Activity, Diet #Pharmacology and Obesity Treatment #Diet and metabolism studies
paper · pdf · doi:10.1093/ptj/83.3.276
Obesity is a worldwide epidemic1 that is characterized by excess adipose tissue and that contributes to numerous chronic diseases2 and early mortality.3,4 This epidemic has received both national and international attention because of obesity's detrimental impact on health, the enormous economic burden it imposes,5 and its increasing prevalence. The adverse health consequences associated with obesity include cardiovascular disease6,7; stroke; type 2 diabetes mellitus8; hypertension; dyslipidemia; cancers of the breast, endometrium, prostate, and colon9,10; gallbladder disease; osteoarthritis11–13 respiratory problems, including asthma14 and sleep apnea15; and perhaps depression.16,17 Furthermore, aerobic capacity and the ability to perform physical activities may be hindered by obesity,18,19 and this may have implications for physical therapists' interventions. In addition to the increased morbidity and functional limitations associated with obesity, approximately 325,000 deaths in the United States each year among nonsmokers are attributable to obesity.20 We will discuss the prevalence of obesity, its etiology in the context of our environment, and the currently available treatment modalities. The most commonly used method today for classifying an individual as overweight or obese is based on body mass index (BMI), a value that is determined by dividing body weight (in kilograms) by the square of height (in meters). In adults, overweight is defined by a BMI of ≥25.0 kg/m2, and obesity is defined by a BMI of ≥30.0 kg/m2, regardless of sex. The World Health Organization distinguishes several BMI categories based on increasing health risks (Table).21 Despite these categorizations, however, the adverse health effects of overweight and obesity occur along a continuum of increasing adiposity. The use of BMI to assess weight-related health risk has gained international acceptance because of the associations between BMI and adiposity,22 BMI and disease risk,2 and BMI and mortality.23 The simplicity of determining BMI, which can be calculated from measurements or self-reported values of height and weight, enables comparisons of various populations throughout the nation and worldwide. The major limitation of BMI is that it does not differentiate between weight that is fat (ie, fat mass) and weight that is muscle (ie, fat-free mass), and therefore may lead to misclassification of very muscular individuals as overweight. In addition, older adults may appear to have a healthy BMI despite having excess fat and reduced muscle mass.24 World Health Organization's Body Mass Index (BMI) Categories Based on Increasing Health Risks21 World Health Organization's Body Mass Index (BMI) Categories Based on Increasing Health Risks21 Waist circumference is another clinically feasible measurement that may be used independently or in addition to BMI25 to assess weight-related health risk. The World Health Organization has identified sex-specific waist circumference values that signify increased health risk (≥80 cm for women, ≥94 cm for men) and substantially increased health risk (≥88 cm for women, ≥102 cm for men).21 Waist circumference correlates well with BMI (r=.84−.88),26 requires only a tape measure, and provides an estimate of abdominal fat.27,28 Abdominal fat is more strongly associated with health risk than fat stored in other regions of the body.29 Although BMI and waist circumference are the recommended30 and most clinically feasible means of identifying patients who are overweight or obese in clinical practice, numerous body composition assessment techniques are available.31 The most accurate techniques, including hydrostatic weighing,32 dual-energy x-ray absorptiometry (DEXA),33 and isotope dilution,34 depend on sophisticated equipment generally available only in research settings. A simple, economical, and potentially reliable technique is skinfold thickness examination performed using calipers.35 The accuracy of this method, however, is compromised in individuals with extreme obesity or altered hydration status, and interobserver variability may be high,36 particularly when different calipers are used. Bioelectrical impedance analysis (BIA)37–39 is another method used to estimate adiposity by measuring resistance to a low-frequency electrical current. The premise of this method is that current flows through aqueous compartments, whereas adipose tissue, which is nonaqueous, impedes the flow. The advantages of BIA include its portability, modest cost, noninvasive nature, the brief assessment time required, and its validity and reliability in many populations.40–43 However, individual variability can be high, and the accuracy of BIA is compromised in situations of altered hydration status44 and extreme obesity.45–47 Obesity is a global problem, affecting an estimated 300 million people worldwide.48 Its prevalence is increasing in both developed and developing countries throughout the world. In the United States, the prevalence of obesity is greater than it has ever been, with striking increases observed during the past 2 decades.49,50 Five large-scale, national surveys conducted in the United States between 1960 and 2000 provided estimates of the extent of overweight and obesity in our nation. These surveys were the National Health Examination Survey (NHES I, 1960–1962); the first 3 National Health and Nutrition Examination Surveys (NHANES I, 1971–1974; NHANES II, 1976–1980; NHANES III, 1988–1994); and the ongoing NHANES, which began in 1999.51,52 In contrast to other surveillance studies, the NHES and NHANES involved measured heights and weights, from which BMI was calculated. The prevalence of overweight (including obesity) among adults 20 years of age and older in the United States changed relatively little between 1960 and 1980, whereas dramatic increases were observed after 1980. As shown in Figure 1, 64.5% of the adult population currently is estimated to be overweight based on data from NHANES 1999–2000,51 as compared with 46% during NHANES II (1976–1980).52 Most of this increase is attributable to a dramatic rise in the prevalence of obesity (ie, BMI of ≥30.0 kg/m2) from 15% during NHANES II to the recent estimate of nearly 31% during NHANES 1999–2000.51 Because overweight and obesity are common health problems, present among nearly 65% of adults in the United States, physical therapists will continue to encounter these individuals in clinical practice for many years to come. Percentage of adults (20–74 years of age) classified as overweight but not obese (hatched bars, body mass index=25.0–29.9 kg/m2) and obese (open bars, body mass index of ≥30.0 kg/m2) in the National Health Examination Survey I (NHES I) and 4 National Health and Nutrition Examination Surveys (NHANES).51,52 The numbers above the bars represent the total percentages of individuals classified as overweight. Obesity is pervasive, affecting people of all ages and at all socioeconomic levels. Results of the Behavioral Risk Factor Surveillance System, a cross-sectional telephone survey of adults, suggest that the prevalence of obesity among young adults 18 to 29 years of age increased 70% between 1991 and 1998.53 Consistent with the data for adults, the prevalence of overweight and obesity among children and adolescents changed very little between the 1960s and early 1980s, whereas dramatic increases were observed during the 1980s and 1990s.54 It has been estimated, using age- and sex-specific BMI criteria, that 10.4% of children 2 to 5 years of age, 15.3% of children 6 to 11 years of age, and 15.5% of adolescents 12 to 19 years of age are overweight.55 This phenomenon among children and adolescents has contributed to unprecedented rates of type 2 diabetes,56,57 a disease formerly referred to as “adult-onset diabetes” because it rarely affected youth. Increasing age is associated with an increase in obesity. Body weights of men and women in the United States increase approximately 9.1 kg between the ages of 25 and 55 years.58,59 These increases in body weight generally are not explained by increases in fat-free mass, because bone mass peaks around 30 years of age and muscle mass plateaus and later declines unless the individual engages in strengthening activities. These changes in body weight and body composition are attributable, in part, to the natural declines in growth hormone, dehydroepiandrosterone, and testosterone with aging. In addition, reductions in resting metabolism alter energy balance and contribute to weight gain. The question has been raised as to whether obesity remains a health risk among older adults. There is evidence suggesting that the optimal BMI range for adults 65 years of age and older is higher than the range for younger adults.60–62 However, a mortality follow-up study of men who participated in NHANES I and NHANES II revealed that indicators of fat mass were positively associated with mortality, whereas indicators of fat-free mass were inversely associated with mortality.63 These findings highlight the importance of body composition assessment and the potential limitation of BMI among older individuals. Excess body fat appears to continue to have adverse health effects into old age, although the relative contribution to ill health may be different than for younger individuals. Additional research is needed to enable us to better understand the relationships among obesity, morbidity, and mortality in older adults. Sex differences also are apparent in the patterns of weight gain and the development of overweight and obesity. These patterns are partially attributable to hormonal differences between men and women before menopause and to hormonal changes in women during menopause.64 During the perimenopausal and postmenopausal periods, many women experience alterations in body weight,65,66 total body fat67 and body fat distribution.68 Wing et al66 reported that premenopausal women between 42 and 50 years of age gained an average of 2.25 kg in 3 years; 20% of these women gained at least 4.5 kg (approximately 10 lb). Based on the NHANES III data set, approximately 70% of women between 45 and 54 years of age is overweight or obese.69 Although increasing adiposity appears to be common after menopause, a great deal of evidence suggests that this phenomenon is neither desirable nor necessarily inevitable.70 In addition to age and sex, race and ethnicity are factors in the prevalence of obesity. Substantial disparities exist among white, black, and Hispanic women, with a higher prevalence of obesity observed among the latter 2 groups.71–74 Some of this difference appears to be attributable to lower rates of physical activity among black women75–77 and Hispanic women.76 Interestingly, however, the health risks associated with obesity also are influenced by race, with black individuals at lower risk and Asians at higher risk compared with whites at the same BMI.78 Additional factors influencing body weight include income and education level, which are inversely associated with overweight and obesity among adolescents and adults. The observed trends in body weight in the United States during the past decade are contrary to the Healthy People objectives of reducing the prevalence of overweight and obesity.79 Healthy People 2000,80 a national health initiative introduced in 1990 by the US Department of Health and Human Services, contained specific goals to be achieved by the year 2000 that would improve the health of Americans. One of these 10-year goals was to reduce the prevalence of overweight among adults from 26% to 20%. Not only was this goal not achieved, but the prevalence of obesity increased 61% between 1991 and 2000.50 A new set of health objectives, Healthy People 2010: Understanding and Improving Health,71 was introduced in 2000, with a greater focus on overweight and obesity. Objectives to be achieved by 2010 include: increasing the proportion of adults who have a healthy body weight to 60% (from approximately 35% in 2000; healthy weight is defined by a BMI between 18.5 and 24.9 kg/m2), reducing the proportion of adults who are obese to 15% (from 31% in and reducing the proportion of children and adolescents who are overweight or obese to (from approximately 15% in These body weight goals have been based on the health that are to our nation these current body weight trends are us from than to these and of the obesity epidemic by physical therapists and other health are as the Healthy People Obesity is the of and factors that in energy and fat The relative contribution of each of these factors has been and although an in the of body weight, the World Health Organization on that and factors (ie, with excess energy are for the dramatic increase in obesity during the past 2 The contribution to obesity has been by of et in which rates for of overweight were as among than at age 20 A follow-up of these individuals the of in body weight study adult revealed a between the weight and BMI, whereas was observed with the These highlight the importance of little or et estimated that factors for to of the variability in also have been in the development of et that the of body weight and fat as well as the of fat gained in to greater than between the of the to overweight or One of the by which body weight is in the of energy It is estimated that approximately of the in energy physical is attributable to is evidence the of in body weight Despite the of in the of body weight, the with which obesity has in the United States and other countries suggests that factors the in the current obesity alterations not occur in the relatively of time during which obesity epidemic and factors are and is recent evidence from and (ie, who are not but who are the same age and were raised from that factors have a greater on BMI than was the current obesity epidemic appears to be the of and factors with The development of obesity is on an between energy and energy during an of The may be as excess energy relative to energy or as energy relative to energy Figure 2 that energy balance can be achieved only when energy and energy are In with the first of (ie, energy be or excess energy is stored as in adipose The of are to energy when are in excess and to energy from this when energy during and of as little as 10 will lead to a weight gain each which can clinically for gain during is characterized by a by which can increase several to increases in In an the ability to excess energy in adipose tissue was for because energy be from this in of this is when is and In addition to as by and growth factors that fat metabolism through One of these is a identified in and by in proportion to total fat Because more obesity is associated with also whereas of patterns The of in include reducing energy and increasing energy Because these effects generally would in weight resistance has been as the by which with Despite the effects of in and the of in of does not appear to a in the etiology of obesity in very of patterns contribute substantially to the development of obesity. 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