I have 2 daughters who have both lost weight. Now one weighs about 120 (lost about 20lbs +), the other 145 (lost about 30 lbs +). Neither are having their periods now. They have gone at least 2 months without one. I don't want to over react, but should I be concerned? Will this all regulate once their bodies have time to adjust?
Assuming that they are not PREGNANT I would say the reason is probably because they are losing weight too quickly.
An EXTREMELY low body-fat percent can stop menses but your girls don't sound at that level.
I almost always skip my period whenever I go on a diet. I went on my first diet when I was about 16 and now I'm 21. Whenever I stabilize or even sometimess gain weight I always return to my normal cycle. However, I've never missed then about two or three. I've always wondered if it was normal but I don't think it's a problem. I would suggest though if they miss more than about three or four I would see a doc.