The 1977 BMI charts developed by the National Center for Health Statistics were revised, using new empirical data from five national health examination surveys, by the Center for Disease Control in 2000.

In comparing the 2000 to the 1977 charts, the CDC notes:

“For matching statures within the range shown, weights in the 2000 charts tend to be higher than weights in the 1977 charts, especially at larger statures and for girls.” This may or may not be the result of the underlying population becoming heavier, since the data sets and statistical procedures used to develop the two sets of charts were not the same. Jump to report.

While the stature for age charts match very closely, the weight for stature charts diverge. The biggest difference is for girls–the 95th percentile of weight for stature in 1977 is almost the same at heights above 110 cm as the 90th percentile of weight for stature in 2000 (Figure 104). Almost every percentile curve has moved out for girls (except the 5th percentile). The difference is less pronounced for boys, with the lower percentiles tracking closely, and only the 90th and 95th percentiles moving out in the 2000 tables (Figure 103).

So a girl that was “obese,” above the 95th percentile in 1977, would now be classified as only “overweight.” If the underlying population is becoming heavier, then heavier weights will fall in the range of “normal.”