Chapter VI Sloka 16

naTyītStu yaegae=iSt n cEkaNtmnīt>, 
n caitSvßzIlSy ja¢tae nEv cajuRn.

n˜tyažnatastu yogo'sti 
na caik˜ntamanažnata× |
na c˜tisvapnažeelasya 
j˜grato naiva c˜rjuna ( 6|16)||

Verily Yoga is not possible for him who eats too much, nor for him who does not eat at all, nor for him who sleeps too much, nor for him who is (always) awake, O Arjuna.

Commentary: In this verse the Lord prescribes the diet for the students of Yoga. You must observe moderation in eating and sleeping. If you eat too much you will feel drowsy, and sleep will overpower you. You will get indigestion, flatulence, diseases of the bowels and the liver. If you eat too little you will get weakness and you will not be able to sit for a long time in meditation. You should eat neither more nor less than what is actually necessary for maintaining the body in a healthy and strong state.

It may mean also that success in Yoga is not possible for him who eats more than the quantity prescribed in the text books on Yoga. They prescribe: "Half the stomach must be filled with food; a quarter with water and the remaining fourth must be empty for the free movement of air."

This is the Mita-ahara or moderate diet for a student of Yoga. If you sleep too much you will become lethargic. The mind will be dull and the body will be heavy. You cannot meditate. If you sleep too little you will experience drowsiness. You will sleep during meditation. 

Keep the golden medium. You will have rapid progress in Yoga.