SB 11.18.34

āhārārthaṁ samīheta
 yuktaṁ tat-prāṇa-dhāraṇam
tattvaṁ vimṛśyate tena
 tad vijñāya vimucyate
Word for word: 
āhāra — to eat; artham — in order; samīheta — one should endeavor; yuktam — proper; tat — of the person; prāṇa — life force; dhāraṇam — sustaining; tattvam — spiritual truth; vimṛśyate — is contemplated; tena — by that strength of the mind, senses and life air; tat — that truth; vijñāya — understanding; vimucyate — one is liberated.
Translation: 
If required, one should endeavor to get sufficient foodstuffs, because it is always necessary and proper to maintain one’s health. When the senses, mind and life air are fit, one can contemplate spiritual truth, and by understanding the truth one is liberated.
Purport: 

If foodstuffs do not come automatically or by token begging, then one should endeavor to keep body and soul together so that one’s spiritual program will not be disturbed. Normally, those who are endeavoring in spiritual life cannot maintain steady concentration on the truth if their mind and body are weakened by undereating. On the other hand, extravagant consumption of food is a great impediment for spiritual advancement and should be given up. The word āhārārtham in this verse indicates eating only to keep oneself fit for spiritual advancement and does not justify unnecessary collecting or warehousing of so-called alms. If one collects more than necessary for one’s spiritual program, the surplus becomes a heavy weight that drags one down to the material platform.