To identify whether the obesity epidemic is entirely a recent phenomenon or a continuation of longstanding trends, researchers supported by the Pediatric Growth and Nutrition Branch analyzed data from a longitudinal study of more than 1,100 children who were born between 1930 and 1993.
For those cohorts:
Among the boys, all of the increase began after the birth year 1970. Among girls, obesity began to rise after birth year 1980, but overweight was already rising as early as the 1930s and 1940s.
The results show that although some rise in body weight is a longstanding trend, most of the child obesity epidemic is recent and sudden (PMID: 23512972).