Sims 3 Jacked up. please, please help.?

ok while i was playing sims 3 . and when i make my family and stuff i can't make them fat or skinny. But when i started to play with the weight thingy, it made my sim anorexic then fat. (when i slid the meter to fat) But when my family was done, started playing it but my family went into a body part separation where her legs went back words and her waist went forward can any one explain this?