Research in context
Evidence before this study
We searched PubMed for studies on national trends in mean body-mass index (BMI) and obesity in China, published from Jan 1, 2010, to March 1, 2021, with no language restrictions, using the search terms ((obesity[MeSH Terms] OR (body mass index[MeSH Terms])) AND adult[MeSH Terms] AND China[MeSH Terms]) AND trend*[Title/Abstract]. We identified several studies that reported a rise in mean BMI and obesity in China until 2013 in both urban and rural areas and across different education groups. Evidence on trends after 2013 in BMI and obesity in China was mainly based on studies in particular regions and from statistical models in global studies. One study reported a steady rise in mean BMI and obesity (defined as BMI ≥27·5 kg/m2) among adults aged 18–80 years during 1993–2015. Another study found increasing trends in the prevalence of obesity (defined as BMI ≥28 kg/m2) among rural men aged 15–49 years during 2010–14. The use of the Chinese BMI cutoff for obesity in these studies, which was proposed in the early 2000s, restricted the ability to compare with data in China collected before 2004 or with data from other countries. The most recent study in China that classified obesity using the conventional WHO definition covered only a 5-year period during 2013–18 and found increasing prevalence; however, this study did not examine long-term trends before 2013, nor the trend in mean BMI. Furthermore, the study used an unconventioal sampling method, leading to an unexpected much lower obesity prevalence than reported in other nationwide surveys in China. To our knowledge, there are no national studies covering a prolonged time period in the years after 2015 for mean BMI or the prevalence of obesity using internationally comparable definitions (BMI ≥30 kg/m2) in China.
Added value of this study
To our knowledge, the present study provides the most up-to-date analyses of long-term and more recent trends in mean BMI and obesity prevalence in China. By using six large national surveys during 2004–18, we examined BMI and obesity prevalence both nationally and by sex, age, urban–rural locality, education, occupation, and geographical region. Our study showed that, in contrast to previous predictions, the increase in mean BMI and obesity prevalence appeared to slow down in China after 2010, when a number of large nationwide prevention programmes targeting non-communicable diseases and obesity were rolled out. However, there were divergent trends in urban and rural areas, particularly among women. Since 2010, the increase in mean BMI and obesity prevalence slowed down substantially in urban men and women, and moderately in rural men, but continued steadily in rural women. By 2018, mean BMI was higher in rural than urban women, but remained lower in rural than urban men. Among women, the mean BMI was persistently lower in those with higher education than in those with lower education across all six surveys, but the inverse was true among men. In China, 85 million adults aged 18–69 years (48 million men and 37 million women) were obese in 2018, representing a more than three-times increase since 2004.
Implications of all the available evidence
Although the total number of adults who were obese reached 85 million in 2018, the rise in mean BMI and obesity appeared to be slowing down in urban China, while in rural China BMI and obesity continued to rise, especially among women. In addition to divergent trends in urban and rural areas, there were also large disparities in BMI and obesity trends by sex, age, and socioeconomic status. Although further monitoring is needed to assess the longer-term trends and changing patterns, the present study findings highlight the pressing need for more targeted health policies to reduce further increases in obesity in the general population, with a gradual shift towards placing more emphasis on rural populations.