Obesity and CV Risk in Ethnically and Racially Diverse Populations

Rao G, Powell-Wiley TM, Ancheta I, et al., on behalf of the American Heart Association Obesity Committee of the Council on Lifestyle and Cardiometabolic Health.
Identification of Obesity and Cardiovascular Risk in Ethnically and Racially Diverse Populations. Circulation 2015;Jul 6:[Epub ahead of print].

The following are five key points to remember about this American Heart Association Scientific Statement on obesity and cardiovascular (CV) risk in ethnically and racially diverse populations:

  1. About 36% of American adults are obese (≥30 kg/m2), which is defined as excess fat tissue accumulation that may impair health. However, simple use of the body mass index (BMI) with thresholds can miscalculate risk of obesity-related illnesses in both directions. The miscalculation is particularly problematic when applied to specific racial and ethnic groups. BMI has a high degree of specificity for adiposity, but a low sensitivity for both men and women. The level of BMI that predicts percent body fat is lower in Asians and Asian Americans, and similarly, the BMI that predicts diabetes is lower in Mexican Americans. Additionally, a BMI between 25 and 30 kg/m2 is associated with lower mortality than normal weight (BMI of 20–25 kg/m2) and a BMI of 30-35 kg/m2 is not associated with increased mortality compared with normal weight.
  2. Visceral adipose tissue (VAT) may better predict CV risk than BMI. VAT likely serves as the site of dysfunctional, hypertrophic adipocytes that promote inflammation, oxidative stress, and production of cytokines and adipokines. But simple anthropometric measures, including BMI, waist circumference (WC), and waist-hip ratio (WHR), alone or in combination with other measures of overall CV risk provides practical guidance for clinicians to risk stratify “obesity.”
  3. Elevated WC and WHR are associated with increased CV risk and premature death independent of BMI. Like BMI, both measures are correlated with overall adiposity, but they are more appropriately used as measures of abdominal obesity, which correlates with the amount of VAT. The cut points for abnormal for the National Institutes of Health (NIH)/National Heart, Lung, and Blood Institute (NHLBI) that distinguish higher and lower CV risk are >102 cm (40 inches) for men and >88 cm (35 inches) for women, which are also used by the World Health Organization (WHO) to predict a high risk for metabolic complications. Lower cut points of >94 cm (37 inches) for men and 80 cm (31.5 inches) for women are used to identify those with increased risk of metabolic complications. The NIH/NHLBI cut points provide poor sensitivity for predicting CV risk and cardiometabolic risk factors. The WHO recommends cutoffs for WHR of ≥0.90 for men and ≥0.85 for women and US DHS are ≥0.95 for men and ≥0.80 for women. Cutoffs of 0.90 and 0.80 are recommended for Asian men and women, respectively.
  4. People who are muscular, but do not have excess adiposity have higher BMI, which allows a number of people to be inappropriately diagnosed as obese, which classically occurs in athletes and also in black men and women who have more fat-free mass. In contrast, prevalence of metabolic syndrome among non-Hispanic whites with a BMI of 25 kg/m2 is comparable to the prevalence of metabolic syndrome among Asians with a BMI of just 20 kg/m2. Asians with a BMI of 24 kg/m2 have a prevalence of metabolic syndrome comparable to non-Hispanic whites with a BMI of 30 kg/m2. Asians and their caregivers may underestimate their cardiometabolic risk because of their relatively low weight and BMI in comparison to other groups.
  5. Magnetic resonance imaging (MRI) and computed tomography (CT) are the current “gold standards” for assessing body composition (i.e., % body fat) and adipose tissue distribution (i.e., VAT and subcutaneous adipose tissue volume). CT can be performed quickly, but involves exposure to ionizing radiation. MRI has the benefit of being radiation free, but is time consuming and each is too costly for clinical use. There is also valuable information available re: visceral fat from ultrasound and DEXA scans, which correlate highly with CT. Bioelectrical impedance analysis of % body fat is convenient and low cost, but much less accurate and reproducible for VAT.

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