What Causes Weight Loss And Ribs Pain?

Iam am 57, and have lost 50 pounds in the past 5 months by changing my diet. Primarily follow the Southbeach program. I am please with the weight loss and most things are normal. However, recently I have experience rib pain in both the lest and right ribs. It's not excercise related. What could be the cause or is it totally unrelated. Weird thing is my wife has been following the same Southbeach program and has lost 45 lbs. She is now experiencing similar rib pain. ???