Changes in BMI parallel changes in living conditions and energy intake over time. (A) Development of body mass index standard deviation score (BMI SDS) of Jena schoolchildren (7 to 14 years of age) between 1880 and 2005. The children’s average BMI SDS values increased slightly in the time period between 1880 and 2005/06, corresponding to a BMI increase of 1.8 kg/m2 (0.14 kg/m2 per decade) in boys and of 2.1 kg/m2 (0.17 kg/m2 per decade) in girls. This increase did not occur continuously. The marked increase in average BMI SDS between 1921 and 1932 indicates nutritional normalization following the famine due to World War I. This was followed by a downward shift in mean BMI between 1932 and 1944, reflecting a deterioration in living conditions during World War II. The marked increase in BMI SDS after 1985 was associated with a substantial increase in prevalence rate of obesity , and is a result of the dramatic changes in living conditions due to the German reunification. (B): Development and association of BMI and energy intake of Jena school children (7 to 14 years of age) between 1880 and 2005 (reproduced with permission from Zellner et al.). The figure shows that BMI values as a surrogate of body fat mass paralleled the changes in energy intake over a time period of 100 years.