BMI underestimates obesity among Singaporean adults

Compared with Caucasian counterparts, Singaporeans seem to have higher percentage body fat (BF%) relative to their body mass index (BMI), a recent study suggests. As a result, measuring the prevalence of obesity using either measure leads to widely different estimates.

“[O]ur study found a large discrepancy between BF% and BMI measurement in Singaporean adults,” the researchers said. “The results confirmed that Singaporean adults have higher BF% at lower BMI compared to Caucasians and that BF% in our population have also increased over two decades.”

The population-based study included 542 community-dwelling Singaporean adults (aged 21–90 years, 43.1 percent men), in whom anthropometry and body composition were evaluated. BMI overweight and obesity were defined according to the WHO and Singapore’s Ministry of Health (MOH) Clinical Practice Guidelines. BF% obesity cutoffs were set at 25 percent for men and 35 percent for women.

The mean BMI in men and women was 25.2±4.9 and 24.5±4.2 kg/m2, respectively, suggesting that by both international and local standards, men were on average overweight, while women were overweight only when using the MOH’s guidelines. [BMC Public Health 2021;21:1030]

At these BMI values, however, BF% measurements were notably higher. In men and women, the corresponding overall BF% was 30.0±5.7 percent and 39.7±5.2 percent, making both sexes qualify for obesity.

The researchers then constructed a forward-backward stepwise linear regression model to assess the correlation between BF% and BMI. Analysis was only possible for the Chinese ethnic group as sample sizes for other ethnicities were too small.

The models found that at the same BMI, Chinese Singaporeans had markedly higher BF% estimates than White, Japanese, and Vietnamese counterparts. Notably, this discrepancy remained true across all BMI benchmarks tested, between sexes, and across all age groups.

This discrepancy between BF% and BMI, as well as the difference in local and international definitions, led to highly variable prevalence estimates for obesity and overweight.

For example, when using the WHO international BMI classification, the overall population-adjusted prevalence of overweight was 34.4 percent, while that of obesity was 12.9 percent. The MOH, on the other hand, found overweight and obesity to be slightly more common, with corresponding prevalence rates of 41.8 percent and 26.6 percent. However, when using BF%, the rate of obesity jumped to 82.0 percent.

“Our study suggests that WHO international and local Health Ministry BMI classification still underestimated the obesity prevalence in Singapore,” the researchers said. "Given the high discrepancy between prevalence of obesity using BMI versus BF%, the prediction equations for BF% from BMI provides a basis and impetus towards establishing healthy body fat ranges in Singapore.”

“Further investigation into the body build, nutrition intake, [and] physical activity level among the different ethnic groups may help understand the relationship between BF% and BMI,” they added.