The BMI values of the lower classes likely declined during the Great Depression.

The BMI values of inmates in the McNeil Island Penitentiary in Washington State declined between the 1860s and the 1910s birth cohorts by 1.44. Furthermore, those who were imprisoned in the 1930s had significantly lower BMI values (by between 0.72 and 1.01) than those who were incarcerated at the end of the 19th century. This corresponds to a decrease in weight of some 2.25kg (4.95lbs) for a man of average height of 173.86cm (68.5inches). The diminution in nutritional status among this lower-class sample is hardly surprising, given the high level of unemployment at the time but has not been verified until now. In marked contrast, the BMI values of Citadel cadets increased by 1.5 units in the 1930s. This divergence in BMI values is most likely due to the different social status, to the different regional origins of the two samples or to both.