Usage patterns
体重を測るto measure/weigh one's body weight
I weigh myself every morning right after waking up.
体重が減るone's body weight decreases
My weight has decreased since I started dieting.
体重を落とすto lose (some) weight
I want to lose five kilograms by summer.
体重を管理するto manage/control one's weight
Athletes strictly manage their body weight.
Expressions
体重をかけるput one's weight on; shift one's weight onto