When changing the percent body fat with a change in body weight the one constant is fat-free body weight.
percent body fat =
= (fat weight in kilograms) / (weight in kilograms) * 100%
weight in kilograms =
= (fat-free body weight in kilograms) + (fat weight in kilograms)
weight in kilograms =
= (fat-free body weight) * 100 / (100 - (percent body fat))
If there is a change in the percent body fat:
final weight in kilograms after change in body fat =
= (100 - (initial percent body fat)) / (100 - (final percent body fat)) * (initial weight in kg)
