February 12, 2021
2 min read
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Chinese adults are more likely to experience detrimental cardiometabolic effects from obesity compared with Black, Mexican American and white adults across a similar weight range, according to data from two large nationwide studies.
“The waist circumference and BMI as diagnostic tools of obesity do not reflect the same level of fat mass and abdominal obesity among different racial/ethnic population[s] leading to various effects on metabolic dysfunction,” Ruizhi Zheng, PhD, of the department of endocrine and metabolic diseases, Shanghai Institute of Endocrine and Metabolic Diseases, Ruijin Hospital and Shanghai Jiaotong University School of Medicine, and colleagues wrote in the study background. “For instance, when Asians and Caucasians have [the] same level of BMI and waist circumference, Asians have significantly lower glucose disposal rates during the insulin clamp, great procoagulant tendency and dyslipidemia than that of white Caucasians. Therefore, BMI and waist circumference may have different indications of cardiometabolic risks across different racial/ethnic population[s].”
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In a cross-sectional study, Zheng and colleagues analyzed data from 98,658 adults who participated in the China Noncommunicable Disease Surveillance 2010 and 51,925 adults who participated in the U.S. National Health and Nutrition Evaluation Survey 2005-2016.
To address multicollinearity of BMI and waist circumference, researchers fitted a linear regression between waist circumference as a dependent variable and BMI as an independent variable, and then obtained “residual” waist circumference by taking the difference between the actual waist circumference and the predicted waist circumference.
“Therefore, the mutual contributions of BMI and waist circumference to adiposity were isolated, of which BMI indicated the overall adiposity and residual waist circumference represented the proportion of waist circumference not related to BMI,” the researchers wrote. “Then, we assessed and compared the associations of obesity metrics, including BMI, waist circumference and residual waist circumference, with cardiometabolic risk factors in Chinese adults and adults with other races/ethnicities.”
Within the cohort, Chinese adults and non-Hispanic Asian adults had lower BMI and waist circumference than the other race groups.
Researchers found that residual waist circumference — the proportion of waist circumference not explained by BMI — was associated with all assessed cardiometabolic risk factors among Chinese men and women (P < .001), but not among adults of other races.
When comparing standardized regression coefficients, researchers found that obesity metrics presented stronger associations with systolic and diastolic blood pressure among Chinese men and women vs. other race groups. BMI and waist circumference also had a stronger effect on triglyceride levels among Chinese men vs. Mexican American, white and Black men.
“The effects of waist circumference and BMI on diseases should not be assessed simultaneously in the same model due to strong multicollinearity of them,” the researchers wrote. “The conclusions of previous studies, which had evaluated the effects of BMI and waist circumference on outcomes simultaneously in a regression model, should be interpreted with caution.”
Perspective
Fatima Cody Stanford, MD, MPH, MPA, FAAP, FACP, FAHA, FTOS
These findings support what we already know about patients of Asian descent. A landmark study in 2004, published in the American Journal of Clinical Nutrition, was the impetus to essentially redraw the BMI guidelines for Asian populations. For Asian populations, the BMI chart has shifted downward. The range for what is considered “normal” BMI for Asian adults is much narrower because of this excess cardiometabolic risk — 23 kg/m² to 26.9 kg/m² is considered overweight, and a person with a BMI of at least 27 kg/m² has obesity.
Clinicians should know about these differences. Race is not a biological variable, but what we do know is there are differences that indeed exist, and studies like this one continue to support that.
That said, we cannot continue to use BMI as a solo tool for assessing people with obesity. We need to use waist circumference, a very easy thing to measure, even via telemedicine with a tape measure at home. This value can be combined with a scale. Put the whole picture together; do not use one number and make a gross generalization about that person. Be cognizant that Asians do have a higher cardiometabolic risk at lower BMI numbers and even lower waist circumference. That means you must be more vigilant with those populations, but this also should not dissuade someone from caring for other populations, such as Black, Latinx and white populations. Watch the trends in things like waist circumference and weight, and look at family history and individual history to help govern a decision about what the next best step is for that patient.
Fatima Cody Stanford, MD, MPH, MPA, FAAP, FACP, FAHA, FTOS
Obesity medicine physician scientist
Massachusetts General Hospital
Harvard Medical School
Disclosures: Stanford reports she is a consultant for Calibrate, Doximity, GoodRX and Novo Nordisk.
Race and Medicine
