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.
How to Best Absorb Magnesium Supplements. Magnesium is needed for hundreds of your body's basic functions, including regulating your heart and blood pressure and helping to metabolize sugar and fats. It also helps your nervous system and combats such problems as insomnia and anxiety.