Bhagavad Gita Verse 16, Chapter 6

naatyashnatastu yogosti na chaikaantamanashnataha |
na chaati svapnasheelasya jaagrito naiva chaarjuna || 16 ||
 
This yoga is not for one who overeats nor for one who fasts, it is not for one who oversleeps nor for one who never sleeps, O Arjuna.
 
na : not
ati : extreme
ashnaha : eating
tu : for
yogaha : this yoga
ati : extreme
na : not
cha : and
ekaantam : ever
anashnataha : fasting
na : not
cha : and
ati : extreme
svapnasheelasya : sleeper
jaagritaha : waker
na : not
eva : only
cha : and
arjuna : O Arjuna
 
When we begin to think that we are progressing in meditation, we may begin to impose severe hardships on the body just because we have seen some others do it. Shri Krishna, in this shloka and the next one, dispels many of these misconceptions. Alternately, we may go in the other direction and begin to neglect the body. In this regard, he advocates a balanced and moderate lifestyle towards achieving our spiritual goals.
 
First let us examine the imposition of severe hardships on the body. Shri Krishna says that meditation will not be easy for one who constantly deprives his body of food and sleep. If the body is deprived of food for a long period of time, where will the mind go when we sit in meditation? It will go to food. The same thing will happen if we forcibly deprive the body of sleep. The minute we close our eyes to meditate, sleep will take over the body. Such hardships become obstacles in meditation.
 
Before the Buddha achieved enlightenment, he went through a phase where he deprived his body of food. When his body began to look like a skeleton, and when he realized that he was almost about to die of starvation, he came to the conclusion that such severe hardships do not in any way accelerate the process of enlightenment. One cannot torture the very instrument that one uses to attain liberation. Like a perfectly tuned musical instrument, the strings should not be too loose or too tightly wound.
 
The other extreme is living life improperly by overeating and oversleeping. Besides the health problems associated with overeating, the additional strain put on the digestive system will draw the mind’s attention away from meditation. Where meditation aims to negate association with the body, overeating pulls the meditator back to the body. Also, oversleeping makes the body dull and taamasic. Instead of meditation uplifting the meditator to a higher level of sattva, oversleeping will also pull the meditator down.
 
So therefore, any deviation from treating the body with care and moderation is not just an obstacle in the spiritual path, it also is an obstacle in any worldly activities. Shri Shankaraachaarya provides a simple formula for moderating our eating habits. He says that one should have a sense of how big one’s appetite is, and then divide it into four parts. Two parts of that appetite should be filled with solid food, one part with liquid and one part should be left empty.