ALSPAC did not collect DXA measures of body composition at 7 or 8 years of age but did collect impedance. An equation has previously been derived to estimate body fat from impednace in adults and it has been shown that this also correlates well in chidlren but this has never been written up. We plan to examine associations between body fat estimated from impedance and boda fat estimated using DXA at all timepoints where both are available.