Fasting is a very integral part of many religions. Individual observe kinds of fast based on personal beliefs & customs.
Some people do fast regularly or some do on special occasions like festivals. In fasting, they do not eat at all, eat once or make do with fruits or a special diet of simple food.
Fasting in Sanskrit is called upavaasa. Upa means “near” + vaasa means “to stay”.
Upavaasa therefore means staying near (the Lord), meaning the attainment of close mental proximity with the Lord. Then what has upavaasa to do with food?
Our most time and energy is spent in procuring food items, preparing, cooking, eating and digesting food. During fasting days time and energy get conserved either no eating or eating simple, light food. Totally abstaining from eating make mind alert and pure. Since it is a self-imposed form of discipline it is usually adhered to with joy.
Also every system needs a break and an overhaul to work at its best. Rest and a change of diet during fasting is very good for the digestive system and the entire body.
The more you indulge the senses, the more they make their demands. Fasting helps us to cultivate control over our senses, sublimate our desires and guide our minds to be poised and at peace.
Scientifically speaking fasting atleast twice a month helps in proper cleansing of body.
Fasting should not make us weak, irritable or create an urge to indulge later. This happens when there is no noble goal behind fasting.
The Bhagavad-Gita urges us to eat appropriately – neither too less nor too much – yukta-aahaara and to eat simple, pure and healthy food (a saatvik diet) even when not fasting.