Protein is a large, complex molecule that must undergo a series of processes during digestion. During digestion and absorption, protein passes through many organs. Once protein is digested, the body can utilize its nutrients to build and repair many of the cells in the body.
Menstrual cramps may be caused by:[5] 1  Endometriosis: The tissue that lines your uterus becomes implanted outside your uterus, most commonly on your fallopian tubes, ovaries or the tissue lining your pelvis. 2  Uterine fibroids: These noncancerous growths in the wall of the uterus may be the cause of pain.
The cramping that usually accompanies the menstrual period is the primary cause of this upset stomach and it can occur before, during or after a womanâs period. However, this nausea could also be caused by excess stomach acid that comes from the changes and imbalance in hormones during the menstrual cycle.