An Ethnic Comparison Study Of Fat And Fat Distribution Between Chinese And U.S.Whites

Background and objectiveThe Chinese BMI cutoffs to define overweight (BMI≥24kg/m2) and obesity (BMI≥28kg/m2) has recently been challenged by several large prospective studies, which support the use of the WHO definition(Overweight:BMI>25kg/m2; Obesity: BMI≥30kg/m2) for Chinese men and women. Obesity is defined as an excess of body fat, not an excess of body weight, and BMI is only a surrogate for body fatness. Furthermore, the WHO definition is based primarily on data from whites. Thus, this dissertation aims to investigate whether ethnic specific BMI cutoffs are needed for Chinese in view of body composition and ethnic comparison between Chinese and whites.MethodsCross-sectional study of1029Chinese from Hangzhou, China and207whites from New York, USA, were voluntarily recruited. Total and regional fat were determined by dual-energy X-ray absorptiometry. Sex-and ethnicity-specific polynomial regression analyses were applied to identify the Chinese BMI cutoffs corresponding to whites for having the same percent body fat (%BF) or percent trunk fat (%TF). Sex-specific BMI prediction formulas were first developed in Chinese using both the linear and quadratic forms of%BF, trunk to legs fat ratio (TLFR), age, and height as independent variables, and then applied to the whites to estimate fat and fat distribution adjusted BMI cutoffs for Chinese. Analysis of covariance (ANCOVA) was used to assess the ethnic differences in fat, fat distribution, and metabolic risk factors.ResultsPolynomial regression analyses showed that Chinese men and women had higher%BF and higher TF%than whites. Corresponding to the white BMIs of25and30kg/m2, cutoffs of22.8and27.8kg/m2were found in Chinese men, and24.3and32.3kg/m2in Chinese women, for having the same levels of%BF. These cutoffs were further reduced to21.4and25.3kg/m2in men, and to21.0and24.7kg/m2in women, when Chinese BMIs were linked to white BMIs for having the same%TF, indicating that central fat distribution differs to a great extent between Chinese and whites. After applying the Chinese-derived BMI prediction formula in whites, linear regression analyses shows that lower cutoffs of22.4and25.7kg/m2in men, and22.5and26.2kg/m2in women, were also identified in Chinese people corresponding to the white BMIs of25and30kg/m2after adjusting for age, height,%BF, and TLFR.Ethnic differences in metabolic risk factors were also identified. Compared with whites, higher metabolic risks were detected in Chinese for a given BMI after adjusting for age and height. Further adjustment for%BF did not change these ethnic disparities. However, after adjusting for%TF, the ethnic differences decreased and become insignificant in triglyceride, high-density lipoprotein cholesterol, and blood pressure (except for systolic blood pressure in men). For fasting plasma glucose, the ethnic differences persisted after adjustment for%BF, but decreased significantly from0.910to0.686mmol/L among men, and from0.629to0.355mmol/L among women, when the analyses were further controlled for%TF. ConclusionCompared with total fatness, fat distribution differs to a greater extent between Chinese and white people, and could in part account for the higher metabolic risk observed in Chinese men and women. Our results support the use of lower BMI cutoffs to define overweight and obesity in Chinese.