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.
If you take a magnesium supplement, you also need to pay attention to your ratios of calcium, vitamin K2 and vitamin D, as these nutrients work together synergistically By Dr. Mercola You don't hear much about magnesium, yet an estimated 80 percent of Americans are deficient in this important mineral and the health consequences of deficiency are significant.