Swami Sivananda suggests that light Sattvik food can be taken before doing Japa. Stomach mustn't be fully loaded before doing activities like Japa, Yoga.
Mentioned in his book "JAPA YOGA - A COMPREHENSIVE TREATISE ON MANTRA SASTRA"
If you are tired of repeating the Mantra at one stroke, have 3 or more
sittings, say, in the morning from 4 O'clock to 7, in the evening from
4 to 5, and at night from 6 to 8. Repeat the Mantra very, very quickly
for sometime, when you find that the mind is wandering much. The
golden rule is to repeat th Mantra neither too slow nor too quick.
Observe the happy medium. The Aksharas of the Mantra should be
pronounced properly. And also, the Mantra should be repeated
Akshara-Laksha. If there are 5 Aksharas or letter in the Mantra it
should be repeated 5 lakh times. This is Akshara-Laksha repetition.
If you sit by th side of a river, lake or well, in a temple, at the
foot or top of a mountain, in a lovely garden or solitary room, the
mind will be focused quite easily, without much effort. If you
repeat the Mantra, when the stomach is overloaded, you will feel
drowsy. Take light Sattvic food. Repeat any prayer and then sit for
Japa. The mind will then be elevated. You will find it pleasant to
rotate the beads easily. You must use yoiur common-sense throughout
your spiritual practice. For sometime you can visit holy places like
Rishikesh, Haridwar, Varanasi, etc., and there you can do Japa on the
banks of holy rivers like the Ganga. You will find marked improvement.
As the mind, while in such sacred places, is free from business,
worries and family-anxieties, you can have an efficient turn of Japa
owing to good concentration there. Record the Japa in your spiritual
And, by "sattvik light food" he means milk and fruits. This is mentioned elsewhere in the same PDF.
- Never let a day pass without meditation. Be regular and systematic. Take Sattvic food. Fruits and milk will help mental
focussing. Give up meat, fish, eggs, smoking, liguors, etc.