नात्यश्नतस्तु योगोऽस्ति न चैकान्तमनश्नतः ।
न चातिस्वप्नशीलस्य जाग्रतो नैव चार्जुन ॥ १६ ॥ (6.16)
But, O Arjuna, Yoga is not possible for one who eats too much, nor for one who does not eat at all; neither for one who habitually sleeps too long, nor, surely, for one who keeps awake.
That food is appropriate for oneself which when eaten gets digested and brings about ability of the body to work.
For one who, ignoring this, eats more through greed, योगः, Yoga; न अस्ति, is not possible, because one gets diseases as a result of ills of indigestion.
Nor is Yoga possible अनश्नतः, for one who does not eat; एकान्तं, at all, because the body becomes incapable of work owing to lack of energy.
Therefore a yogi should not eat either more or less than what is appropriate for himself.
Or, the idea is that Yoga is not achieved by one who eats more or less than the quantity of food needed.
Similarly, न एव, there is surely no Yoga for one who habitually sleeps too long; or जाग्रतः, for one who keeps awake too long.
‘O Arjuna, be careful’–this is the intention.
One of the च (and) in the second line of the verse is meant for conjoining the transgressions of the limit of food; the other च in the later half of the verse is meant the unmentioned defects as have been stated in the Markandeya PuraNa.
O emperor, a yogi should not practice Yoga for the realization of the Self when his belly is inflated, when he is hungry, when he is exhausted or when his mind is troubled. Nor when it is too cold, nor when it is too hot, not when it is both cold and hot, not when it is windy–meditation should not be undertaken during these periods.
Krishna thus states the exclusions from Yoga and proceeds to speak of coming into association with Yoga for those who observes the rules.
युक्ताहारविहारस्य युक्तचेष्टस्य कर्मसु ।
युक्तस्वप्नावबोधस्य योगो भवति दुःखहा ॥ १७ ॥ (6.17)
To one whose food and movements are regulated, whose effort in works is moderate, and whose sleep and wakefulness are temperate comes Yoga which is the destroyer of sorrows.
(युक्त-आहार-विहारस्य:) आहार means what is gathered in viz. food; विहार means movement ie. walking; to one in whom these two are regulated (युक्त), of regular measure.
Similarly (युक्त-चेष्टस्यः) to one whose effort (चेष्टा) is moderate (युक्त), havin a fixed time, even in other कर्मसु, works, such as repetition of ॐ, recitation of upanishads etc.
Similarly, (युक्त-स्वप्न-अवबोधस्य:) स्वप्न here means sleep, and अवबोध means wakefulness, to one in whom those two are temperate (युक्त), regulated in time.
To him भवति, comes, योगः, Yoga; समाधि becomes accomplished through the intensity of spiritual disciplines; not to anyone else.
What is the result of Yoga that is thus accomplished through special effort?
In answer Krishna says: दुःखहा, (it becomes) a destroyer of sorrows; ie. it becomes cause of cessation of sorrows, together with their roots.
Because it leads to the Knowledge of Brahman, which is the means of destroying nescience, the source of all sorrows of mundane existence.
As for the regulation of food here it is as has been stated before in Yoga:
Half the stomach is for food together with curries; the third quarter is for water. However the fourth quarter one should leave for moment of air.
The regulation about walking is that, ‘one should not walk for more than a योजन (about 9 miles, some say it is a bit less than 5 miles).
The regulation about diligence in work consists in avoidance of garrulity (excessive talkativeness, especially on trivial matters) etc.
The regulated time for sleep and wakefulness is this–dividing the night into three parts, remaining awake during the first and the last part and sleeping in the middle part.
These are the guidelines given in the Yoga Sutra.