The question is
How much amount/quantity of food to be eat per day for spiritual person?
Sri Krishna says in BG, as follows:
नात्यश्नतस्तु योगोऽस्ति न चैकान्तमनश्नतः।
न चातिस्वप्नशीलस्य जाग्रतो नैव चार्जुन।।6.16।।
But, O Arjuna, Yoga is not 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.
So spiritually inclined person should partake moderate food.
युक्ताहारविहारस्य युक्तचेष्टस्य कर्मसु।
युक्तस्वप्नावबोधस्य योगो भवति दुःखहा।।6.17।।
Yoga becomes a destroyer of sorrow of one whose eating and movements
are regulated, whose effort in works is moderate, and whose sleep and
wakefulness are temperate.