4·1 Percentage Body Fat
In this study, we established the relationship between BMI and BF% in Singapore Chinese, Malay and Indian adults. We compared the estimated BF% with other ethnicity, and also with an earlier study on Singapore population from 20 years ago. Comparing among ethnicities, Singapore Chinese, Malays, and Indians are found to have higher BF% compared to Caucasian. This supports the findings from the Singapore study in 2000 (24) and other reports that some Asians population have greater fat mass than Caucasians(14, 32-34). However, there are other contrasting findings from other Asian populations, such as Vietnamese(31) and Polynesian(35) population that for similar sex, age, and BMI, the BF% was lower compared to Caucasians – showing the ethnic diversity in percentage body fat in Asia.
Our finding updates the 2000 report (24) in that current cohort of Singaporeans have higher BF% at matching BMI, age and sex compared to the cohort from 20 years ago, except within the high BMI range(35-40kg/m2) and Malay men at BMI 18·5kg/m2(24). In our study, Indians have the highest BF%, followed by the Chinese, then Malays. The 2000 study reported that Indians had the highest BF%, but with Chinese having the lowest BF%(24). The difference in BF% among different ethnic groups in the same population was previously reported(34). The changes among Singaporeans may be due to changes in energy balance. Average daily energy intake increased 10·3% from 2004 to 2010 with majority (59·4%) of the population exceeding the daily recommended energy intake(36). This increase in energy intake was not offset by the subsequent 5% reduction in average daily energy intake between 2010 to 2018(37). The Chinese (578kcal) had the highest increase in energy intake (Malay: 533kcal; Indians; 429kcal)(36), which could explain Chinese overtaking the Malays in BF% ranking.
4·2 Prevalence of overweight and obesity
The population-adjusted prevalence of overweight and obesity of Singaporeans, classified using WHO international BMI categories, are 34·4% (men: 39·1%; women: 29·9%) and 12.9% (men: 14.9%; women: 11.0%) respectively (Table 4). However, using the Singapore Health Ministry BMI cut-off, the population-adjusted prevalence of overweight increase to 41·8% (men: 44.5%; women 39.3%), and obesity 26·6% (men: 30·7%; women: 22·8%) (Table 4). When adopting BF% criteria (>25% in men and >35% in women), population-adjusted obesity prevalence was substantially higher at 82.0% (men: 80·2%; women: 83·8%) (Table 4). The corresponding high population -adjusted prevalence of WC>80cm for women and >90 cm for men (59.1% overall, 55.7% for men and 62.3% for women in Table 4) suggests that central obesity account for much of this excess body fat in our population. Such substantial higher prevalence with BF% criteria had also been reported in the Vietnamese(31). It is well-known that BMI, though highly specific, has low to moderate sensitivity when defining obesity and underestimate prevalence of adult excess body fat, particularly in Asians(31, 38). While the Chinese and Koreans have proposed population-specific BF% cut-off(33, 39), there is yet no Asian consensus in BF% cut-off point. Our finding is a step towards such a consensus.
A previous study reported that the lowest all-cause mortality rate in Singapore Chinese was at BMI 18·5-19·9kg/m2, with mortality rate significantly increased at BMI ³26·0kg/m2 for non-smokers(16), which is lower than the WHO Asian recommendation(13). Using our derived equation, BF% at BMI 18·5-19·9kg/m2 equates to 20·9-23·2% in Chinese men and 32·8-34·8% in Chinese women aged 50 years. At BMI 26kg/m2, BF% equates to 30·4% in Chinese men and 40·9% in Chinese women, which is about 5% higher than the WHO BF% cut-off. Using the criteria of BF% ³30·4% in men and ³40·9% in women, 45% of men and 44% of women have increased mortality risk. These estimates are much higher than the prevalence based on BMI ³30kg/m2, but much lower than using the WHO BF% cutoff. Differences in prevalence based on BMI is expected because the relationship between BMI and body fat content varies according to body build and proportion(2). People with low relative sitting height will have a relatively low BMI compared to their BF%(40), but our Asian population have high relative sitting height(41). The smaller body frame of Singapore Chinese partially contributed to their having higher BF% at the same BMI(41). Physical inactivity is likely another contributing factor. The 2010 National Health Survey found 39·1% of Singaporeans did not meet the recommended physical activity guidelines(42). The increase in energy intake and lack of physical activity could explain the high BF% in Singaporeans. Such high BF% in Singaporeans may explain the leading contribution of cardiovascular disease and cancer to disease burden(43). Our study suggests that WHO international and local Health Ministry BMI classification still underestimated the obesity prevalence in Singapore(24). 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.
4·3 Strength and limitation
The strengths of this study are its population-based, random selection of participants and hence representativeness and validity of data. The ideal method to determine body composition is the multi-compartment model(30), however such method is inaccessible, expensive and require participants to undergo multiple test. DXA, though may have its limitations, has been used in multiple national population surveys and considered the “gold standard” for measuring body composition parameters(31, 44). There are some limitations to this study. Though due to random sampling, the ethnic distribution of the study population was similar to that of Singapore’s, the sample size of Malays and Indians were not adequately powered to make statistical comparisons between ethnic groups. Hence, our findings on ethnic differences in obesity need to be confirmed with a larger sample of Malay and Indian ethnic groups. A thorough investigation into the nutrition intake and physical activity may help understand the large discrepancy between BMI and BF%. The ideal approach to define threshold for obesity is based on the relationship between BF%, all-cause and cause-specific mortality in a long-term prospective study.
In conclusion, our study found a large discrepancy between BF% and BMI measurement in Singaporean adults. 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. Further investigation into the body build, nutrition intake, physical activity level among the different ethnic groups may help understand the relationship between BF% and BMI.