Why do we fast?

Today is the first day of Ramazan (or Ramadan), the ninth month of Islamic Calender.

Just yesterday people at my office asked me, "Why do you fast?"
And before I could reply I got an answer from another colleague, a non-muslim, saying, "Prophet Mohammed(Peace be Upon Him) Ke liye." That is, "For Prophet Mohammed(pbuh)."
Another friend also said something which unfortunately I couldnt understand and he wouldnt repeat again.

This is not the first time that I was asked this question. Another answer which I have heard from a friend is, "When you fast you know what its like feeling hungry and you remember those unfortunate people on earth who are poor and hungry and then you will help them more."

Some say, "Fasting is a way of worship, in almost all religions, this way you come closer to God."

In a way all these reasons or explanations look fine, but either these reasons are empty or incomplete.

Fasting, as defined in Islam, is to 'completely' abstain from food, drinks, intimate intercourses and smoking, from the break of the dawn till the sunset for the entire month of Ramadan, which basically is of 29 or 30 days.

I said, "The primary and the only reason a muslim observes fasting is to increase the fear and/or the love of God in him."

The ordain of Fasting in Ramadan comes in the Holy Quran:
" O you who believe! Fasting is prescribed to you as it was prescribed to those before you, so that you may develop Taqwa. (self restraint) [2:183]"
When the companions of the Prophet(May Allah be pleased with them) asked what is Taqwa to Prophet Muhammad(pbuh), the Prophet (pbuh) replied "Taqwa ha huna", "Taqwa ha huna", "Taqwa ha huna" (Taqwa is here) pointing to heart (3 times).

So a muslim only fasts to attain the Taqwa, which is nothing but God Consiousness.
All other benefits comes attached to it but they are not the reason why a muslim fasts.

Some ask, "How come staying hungry in the day increases fear of God in you?"

Simply staying hungry doesn't.

Abu Huraira(May Allah be pleased with him) related that Rasulullah(pbuh) said: Many people who fast get nothing from their fast except hunger and thirst, and many people who pray at night get nothing from it except wakefulness (Darimi).

Meaning apart from abstaining from food and desires, we should abstain from backbiting, gossiping, usage of harsh words, vulgarity and all such things that nullifies fasting.
And we should follow the prayers in time and the special night prayer of Ramazan, called as Taraweeh, is also mandatory. Basically the heart and mind should be filled with humility.
Only then the true values of fasting can be attained.

I need not list the worldly advantages of fasting and control. It is known to all.

Hope this article was useful.
One suggestion at the end:
Just yesterday my friend was saying, "People who have a little knowledge never think or never take interest in things."
And I agree with him.
That is the reason why people who gave answers above never increase their knowledge database as they think they know the complete answer but in fact they don't.
So never be complacent with what you know, as there is a ocean to be known about.