+++
Source: from SM library's "Spell Books" section: Aji-ajian - Indonesian rare spells I've collected over the years. the translation from Indonesian to english are mine, so pls pardon the grammar and errors.

In magical art of Kejawen, fasting periods vary greatly from one day to 30 days, some spells/ajian requires longer period of regular fasting disciplines which can go on for months and even years. Fasting usually begins from dawn to sunset. Some spells/ajian requires a non stop fasting (without sleep) from a whole day (24 hours) to up to 7 days, in meditation of the intend of what the magician intend to achieve.

Different types of fasting according to Javanese art of Kejawen:

Simple Fasting: no food or drink and refrain from evil doing.
Ngrowot : vegetable based food diet during fasting.
Mutih : Food diets based on white rice with plain water without sugar nor salt.
Ngebleng : Fasting without any food nor water(without a break/allowed to exit during fasting/toilet) in a room.
Pati geni : Fasting without food nor water in a dark room (without a break/allowed to exit during fasting)
Ngalong : Food diet based only fruits during fasting period.
Ngidang : Food diet of leafs only - must be eaten using mouth with hands firmly tied behind at all times.
Nglowong : No food, no drink, no sleep however you're allowed to wonder around/travel.
Ngepel : Food diet portion of the size of one's fist (usually a fistful of white rice).
Ngasrep : Cold food and drinks only. No salt, sugar nor spice.
Mendem (ngluweng) : Meditation under earth (inside dugged hole) no food/drink.
Nguda-uda : Cutting back food/water consumptions, promote kindness, and offer daily praise and worship to God.

One translation of a kejawen spell:
AJI BRAJAMUSTI (Brajamusti Spell)
In the ancient times, Aji Brajamusti are known to be one of the top warrior's potent and reliable arsenal since this spell believed to be a powerful shield used in war. The very few person who acquired this spell successfuly were granted a physical and magical power only few can compete with. One function of Brajamusti spell were to imbue the body and hands with the power of invincibility. All kinds of weapons becomes impotent when used againts the spell owner.

To acquire Barajamusti spell (note: may be incomplete):
a. 7 days fasting every month for a period of one full year, or, 40 days fast for every one year.
b. During fasting, at a time of prayer - a mantra is to be recited for 41 or 100 times.
c. At the end of the day of fasting, recite the matra once then transfer breath to both hands. At those times the occult power within body will raise, flow freely and grow stronger.
d. Recite "ya qawiyyu ya matiin" 1000 times

Mantra of Aji Brajamusti:
”Bismillahirrohmanirrohiim, Sun matek aji ajiku Brajamusti, Terap-terap, Awe-awe, Kuru-kuru, Griya gunting drijiku, Watu item ing tanganku, Sun taj antem, Laa ilaaha ilalloh Muhammadur rasululloh."

note: spell above were originally Hindu - without the moslim conversion so the original version of the incantation may be written like this:
(God almightly) Sun matek aji ajiku Brajamusti, Terap-terap, Awe-awe, Kuru-kuru, Griya gunting drijiku, Watu item ing tanganku, Sun taj antem,(Great of thy Lord, power and glory - Muhammad prohet of God)
+++

In your opinion, how does fasting work to benefit a magical working?