Our stomach is in the shape of a bag. When stomach is empty , it will shrink. While it is full with our meal, it will increase its size, to around 1.5L. Every minute, the muscle will move / squeeze 3 times automatically. This rhythm goes in line with the signal from the Vagus nerve. When we are feeling stressed, Vagus nerve will increase the signal sending over, hence the stomach wont be functioning as it is usually, causes discomfort.
After meal, it will take around 70 to 80 minutes to push all the digested food to the intestines. When the stomach is complete empty, after some time, the muscle will work harder to clear any waste to keep the stomach clean. However, if we eat late at night, or just before we sleep, the digestive system will be weaker, not being able to sleep well, the stomach wont be emptied, and we will feel more tired the next day.
While yoga, through twisting, forward and back bend , we stimulate the movement of the stomach muscle. It will enhance the digestive system greatly.
It is always good to wait until all the food to be cleared from our stomach before any yoga practice, else we will interrupt the digestion process or experiencing some heartburn sensation.