Racial and ethnic differences in measures and effects of obesity

Abstract

Epidemiologically, obesity is classified into general and central obesity. Body mass index (BMI) is commonly used because data on central obesity are scarce. For the same BMI, Asians have 3-5 percentage points higher in body fat and larger waist circumference (WC) than Caucasians. Although obesity and its indices are all continuous variables, cutoff points are needed to define overweight and obesity. The cutoff levels are lower for Asians but % body fat/BMI ratio varies within Asians, Caucasians and the same ethnic group (e.g. Chinese in different regions). Obesity increases the risks of cardiovascular diseases, type II diabetes and some cancers. Most of the evidence has come from Caucasian populations. Studies, especially prospective studies, designed to examine ethnic differences are scarce. Evidence predominantly based on BMI and western populations cannot show clear regional or ethnic differences for colorectal, breast and prostate cancer. Measures of central obesity (WC and WHR) may be more strongly associated with type II diabetes than BMI, but the relationships for hypertension and dyslipidaemia were similar. The relationships of BMI, WC and WHR with cardiovascular outcomes are broadly similar. The differences are unlikely to be of clinical and public health significance. The Asia Pacific Cohort Studies Collaboration (APCSC), a meta-analysis based on individual data, showed no significant regional (Asian and Australasian) differences. But regional differences are not racial/ethnic differences. Baseline indices may not reflect lifelong obesity status. Changes of body weight/fat before baseline and during follow up can have major impacts on disease burden and mortality. The growing obesity epidemic in the West has started a few decades ago and may take a few more decades to show its full impacts. In the East, the epidemic is at an earlier stage. Results on racial/ethnic/regional differences must be interpreted cautiously.