Fasting in Sanskrit is called उपवास. उप in Sanskrit means ‘near’ and वास means ‘to say’. The literal meaning of the word is to stay near. Upvaas therefore means staying near the deity, meaning the attainment of mental proximity with the Lord.
It is mentioned in the following verse as,
उपावृत्तस्य पापेभ्यो यस्तु वासो गुणैः सह ।
उपवासः सविज्ञेयः सर्वभोगविवर्जितः ॥
Upavruttasya papebhyo yastu vaso gunaih saha
upavasah savidyeyah sarvabhogavivarjitah
Fast is observed by a virtuous person who is free from sin. In that state one should abandon all bhogas (luxuries) including eating.
Importance of fast
Fasting is done for many reasons- to please the Lord, to discipline oneself and even to protect, to cleanse the body once every week etc. It saves various types of energies, time and also effort related to food taking. But generally it is considered as a measure for removing sin in Gautama Dharmasutra.
In Brihadaranyaka Upanishada it is mentioned as the way to god.
तमेतं वेदानुवचनेन ब्राह्मणाविविदिषन्ति ।
यज्ञेन दानेन तपसाऽनाशकेन
Tametam vedanuvachanena brahmanavividishanti
Yadyena danena tapasa nashakena
Believing Vedic sacrifices, donation, penance and fast are the ways which lead us to god.
In Mahabharata it is included in the types of penance. It is foremost and important among these types. In Gruhya sutra it is said that, fast is the food cooked of the grains which are useful to sacrifice.