What is the purpose of fasts Hindus?
The purpose of fasting is not to starve oneself. A fast is symbolic of self-control. Since food is the most common weakness in mankind, control over eating is considered difficult. There are ample examples in the Puranas that saints and sages learnt to control their physical and mental self through fasts. Thus they purified their mind and soul and developed divine powers.
In the Yajur-Veda, 19/30, it is said:
Mankind develops the ability for progressive living through fasts that serve as diksha (initiation). From diksha one moves to dakshina, that is, whatever one does one finds success. From this, faith and devotion grow, and from them, one attains truth or one's aim in life. This is the basic conclusion.
One should not compromise with moral responsibilities and character in difficult situations. The fulfillment of these responsibilities devotedly is the purpose of making a resolve, or observing a fast. Living by resolutions and beliefs and adopting actions that lead us to our aims is important.
To overcome imperfections and tensions that are a part of modern life, the best solution is self-purification through fasting. The use of cereals in the diet produces toxins, which make one lazy and inefficient. These also neutralize spiritual energy generated through prayers and devotion to God. Through fasting, toxins are removed and the mind and body feel better. Self-confidence grows. One develops greater harmony. These, in turn, develop other abilities and powers within a person. Through patience, energy is conserved. Thus fasting helps protect a person and makes him more efficient.
In the Bhagavad Gita, it is said that the best way to control your senses and the mind is too fast.
Science too commends control over diet. By fasting once a week, one is able to rest organs within the body. This promotes good health and long life. Through fasting one also benefits emotionally and spiritually.
The purpose of the fast is not to ignore the body, but rather a means to achieve a particular aim in life. It is the firm resolution and the steps taken to achieve it that benefits the person.
Lord Buddha resolved that whatever happened, he would not leave his asana until he had attained nirvana. He was unmindful that the muscles and fat in his body would waste away. The bones would get porous. He would shrivel without food and drink. But he did not move from the asana. With this firm resolution he attained nirvana.