Are only children in China more likely to be obese/overweight than their counterparts with siblings?

Family planning policy in China has resulted in a large number of one-child families. According to Becker's "quantity-quality trade-off" theory there is an inverse relationship between the number of children in a family, and spending per child. We test whether this has led to significant differences in the height, weight and BMI of only-children compared with children with siblings in China using 4414 observations derived from four recent waves (2004, 2006, 2009, and 2011) of the China Health and Nutrition Survey. We use propensity score matching and instrumental variables to control for the possible endogeneity of the number of siblings. Results show that only-children are significantly heavier (1.88 %-3.86 %), and have higher BMI (2.59 %-3.50 %). Moreover, they are more likely to be obese than children with siblings (2.33 %-3.00 %). Further analysis shows that these differences in health outcomes might be attributable to higher consumption of animal-source food (23.90-27.13 g), a higher frequency of eating western fast food (0.48-0.70 times/3-month) and drinking sweetened soft drinks (0.29-0.36 times/month), a higher share of meals eaten away from home (4.67 %-5.31 %), and more sedentary activity (20.04-34.35 minutes/week) by only children. Our study indicates that the growing share of only children due to China's family planning policies also contributes to the increasing prevalence of overweight and obesity in China. This policy has been eased in recent years, which might slow the increase in the prevalence of overweight and obesity and thus reduce the corresponding health burden for Chinese society as a whole.