Assessing Prevalence and Trends in Obesity Navigating the Evidence (2016) / Chapter Skim
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Pages 27-56
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From page 27... ...
• Development, growth, and maturation that occur during child hood and adolescence can affect the assessment of obesity status. • For children and adolescents, BMI must be compared to a reference population for classification, the most common of which is the 2000 Centers for Disease Control and Prevention BMI-for-age growth charts.
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From page 28... ...
Approaches to Assessing Adiposity and Obesity Status Obesity status is assessed in clinical, research, and public health settings through a variety of approaches. Some evaluate body composition, differentiating lean body mass from adipose tissue.
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Bioelectrical Impedance Analysis In a bioelectrical impedance analysis (BIA) , an electrical current is sent through the body and the measured resistance to the current is used to calculate total body water, lean body mass, and fat mass (Kyle et al., 2004a)
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From page 30... ...
Various percent body fat cut points have been used to classify obesity using skinfold thickness. Although skinfold thickness measurements are inexpensive to perform, their reliability is particularly dependent on the training and expertise of the person taking the measurement (Oppliger et al., 1992; Shaw, 1986)
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From page 31... ...
. BMI does not differentiate between lean body mass and adipose tissue and does not reflect body fat distribution.
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From page 32... ...
The use of BMI among older adults may not adequately reflect changes in body composition, as lean body mass has a tendency to decrease and adiposity can increase as a person ages and can occur in weight-stable individuals (Ding et al., 2007; Hughes et al., 2004; Zamboni et al., 2003)
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From page 33... ...
infants and toddlers use such terminology. Given the measure of relative weight commonly used for this age group, "high weight-for recumbent length" has been used to classify high weight status in lieu of the term "obesity" (Ogden et al., 2014)
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. TABLE 2-1 Classification of Adult Weight Status Using Body Mass Index Cut Points Classification BMI Ranges (kg/m2)
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. In females but not in males, percentage of body fat increases with advancing puberty (Xu et al., 2012)
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, the 2000 CDC sex-specific BMI-for-age growth charts are most commonly used to classify the obesity status of U.S. children and adolescents.2 In its current form, obesity classification in children is statistical -- that is, it is a comparison to a distribution that previously existed in a population -- although elevated values have been associated with various health risks (Freedman et al., 2015b; Kurniawan et al., 2014; Weberruß et al., 2015; Weiss, 2007)
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SOURCE: CDC, 2010. is 120 percent of the 95th percentile on the CDC growth charts (Flegal et al., 2009)
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SOURCE: CDC, 2014. BOX 2-2 BMI-for-Age Percentiles A child's BMI is typically compared to the 2000 CDC sex-specific BMI-for age growth charts for weight status classification.
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Trends based on nationally representative data show that prevalence is substantially higher than it was 40 years ago among both children and adults (Fryar, 2014a,b) (see Figures 2-2 and 2-3)
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The differences in obesity status classification are explained earlier in this chapter. 4 Two caveats are associated with this statement.
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. For children and adolescents, evidence suggests that obesity is associated with both an increase in cardiovascular risk factors and structural cardiovascular changes, such as increase in vascular intimal thickness and retinal vascular changes (Freedman et al., 2015b; Kurniawan et al., 2014; Weberruß et al., 2015)
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Although not all comparisons are evaluations of health disparities, the assessment of health disparities typically rely on demographic characteristics (see Box 2-4)
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. Assessment of body composition also suggests that after age 11 years, males generally have higher fat-free mass than do females, and females generally have higher total body fat and percent body fat compared to males (Borrud et al., 2010)
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In comparing prevalence only by sex (irrespective of race, age, or other demographic factors) , men and women appear to have relatively similar obesity prevalence estimates (Ogden et al., 2013)
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Age also is the determinant used to transition a young adult from the reference population-based obesity classification approach to the single BMI cut point (i.e., 30 kg/m2)
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For nationally representative data based on measured heights and weights, participants are often categorized into groups that may encompass very different life stages. For example, a child age 6 years may be very different than a pubertal child age 11 years in terms of adiposity and interpretation of BMI.
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From page 47... ...
As was discussed with age, the subgroup comparisons bring to light differences in estimates of obesity prevalence across the evaluated groups. Uncovering the relationship between race, ethnicity, and obesity can be complicated by methodologic and analytic decisions.
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Chapter 3 highlights the variability in methodologies for collecting data related to socioeconomic status in studies of obesity. Childhood obesity estimates are often evaluated by a measure of familial or community-level socioeconomic status.
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The relationship between SES and obesity in adults is complex and appears to interact not only with race and ethnicity, but also with sex. Based on 2005 to 2008 nationally representative data, obesity prevalence was similar among men across income levels, but was significantly higher among non-Hispanic black and Mexican American men of higher income (Ogden et al., 2010)
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2015. Cardio metabolic risk screening among adolescents: Understanding the utility of body mass index, waist circumference and waist to height ratio.
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2009. Characterizing extreme values of body mass index-for-age by using the 2000 Centers for Disease Control and Prevention growth charts.
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2015b. Interrelationships between BMI, skinfold thicknesses, percent body fat, and cardiovascular disease risk factors among US children and adolescents.
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2001. Lower BMI cut-off value to define obesity in Hong Kong Chinese: An analysis based on body fat assessment by bioelectrical impedance.
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2007. Body mass index as a predictor of percent fat in college athletes and nonathletes.
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2013. Bioelectrical impedance analysis to estimate body composition in children and adolescents: A systematic review and evidence appraisal of validity, responsiveness, reli ability and measurement error.
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2007. Comparison of body mass index, waist circumference, and waist/hip ratio in predicting incident diabetes: A meta analysis.
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