What Causes Weight Gain After A Kidney Transplant?

My wife s weight has been 130-138 #s for 25 years. She is 48 years young and had a kidney transplant 5 years ago. three months ago her weight started climbing rapidly. she now weighs 155 #s. She is 5 5 . She has always been very muscular. She now has no definition and her waste has gone from 28 to 34 . I am concerned that something serious is going on. She does not eat much but what she eats is high calory foods.