Does income have a non-linear impact on residents' BMI? Re-examining the obesity Kuznets curve

After more than 40 years of growth, the income of Chinese residents has greatly increased; however, the problems of overweight and obesity among residents have become increasingly prominent.

We used data from the China Family Panel Studies (CFPS) to study the relationship between residents' income and obesity using the instrumental variable (IV) method.

The impact of income on residents' body mass index (BMI) is an inverted U-shape; that is, when income is low, BMI significantly rises with income, and when per capita income exceeds 57,066 yuan in 2023 prices (equivalent to 8,098 dollars), further increases in income will lead to a decrease in BMI.

The results suggest that the impact of income on resident obesity may be related to dietary behaviour and health investment. Although income increases the likelihood of health expenditure and exercise, it has an inverted U-shaped effect on whether residents consume fish, meat, fried or pickled foods, and dine out. That is, in the low-income stage, income mainly increases consumption of unhealthy foods such as fish, meat, and fried and pickled foods, leading to a significant increase in BMI. In the high-income stage, residents reduce consumption of large amounts of fish and meat, pay more attention to healthy diet and healthcare, and increase exercise, which leads to a decline in BMI and an overall inverted U-shaped impact of income on obesity. Further heterogeneous analysis showed that income has a greater impact on obesity among rural residents, those aged 50 years and older, and those with low education levels. Finally, this study provides relevant suggestions for the prevention and control (P&C) of obesity among urban and rural residents.