Yoga exercises could stimulate the passage of (green) food and/or (originally green) bile through your bowel, and then either the food or bile would color the stool green. If stools are loose and contain undigested food, you are losing nutrients this way.
Excessive use of magnesium supplements can be toxic. The upper limit -- the highest dose a person can take -- of magnesium supplements is: 65 mg/day for children ages 1-3. 110 mg/day for children ages 4-8. 350 mg/day for adults and children ages 9 and up.
Review by Dani. I began taking magnesium oxide for my constipation-predominant IBS about a week and a half ago, and so far, so good. My doctor recommended I start with 750mg (three 250mg pills) twice a day-which was too much (diarrhea). I cut back to 750mg once a day, at bedtime. This seems to be the right dosage for me.