In the linked study (doi: 10.1136/bmj.a802), Funatogawa and colleagues compare growth curves of body mass index from children to adolescents, and then to young adults, in Japanese girls in birth cohorts from 1930 to 1999.1 The authors find that obesity in childhood fails to predict obesity in adulthood. Their finding begs a wider question about the meaning and effects of excess body weight in children, and whether monitoring the prevalence of childhood obesity is worth while.

This study, which repeatedly examined cross sectional samples from the 1930s to the 1990s, found that although body mass index increased in girls aged 5-12 years in each decade, it did not translate into higher body mass indexes in women aged 17-25 years a decade or so later. If anything, as the children became fatter the young women became thinner. The interpretation given in the paper is that, for girls (but not, apparently, boys), …