It is a known fact that in pre-Islamic Arabia, it was a custom to train horses for battle by
making them fast and run against the wind. Fasting was prescribed to humans to learn self
"O you who believe fasting is prescribed to you as it was prescribed to those before you so that you can learn self restraint". (Quran 2:183)
The Arabic word is Taqwa is translated in many ways including God consciousness, God fearing, piety, and self restraining. Thus we are asked to fast daily for one month from dawn to dusk and avoid food, water, sex and vulgar talk during that period. In addition to this obligatory fasting, we are advised to do non-obligatory fasting on Mondays and Thursdays and the last 10 days of the month of Shaban, and 9th and 10th day of Moharram.
But why do we need to fast? It is our experience that temptations and ways of the world tend to spoil out purity and austerity. Thus we indulge in food all of the time, snacking and nibbling the whole day, leading to obesity. We drink too much coffee, or tea, or carbonated drinks. Some sexaholics can not stay away from sex unless they do it at least once or more a day. When we argue, we leave our decency aside and resort to vulgar talk and even physical fighting.
Now when one is fasting, he or she cannot do all of that. When he looks at the mouth watering food, he cannot even taste it and he has to give up snacking and nibbling as well as smoking cigarette if he does. No constant coffee, tea or Coke drinking either. Sexual passions have to be curtailed and when he is provoked to fight, he says "I am fasting that I cannot respond to your provocation".
To achieve God consciousness or God nearness, a better word, we are advised to do additional prayer and read the Quran. The medical benefits of fasting include lowering blood pressure, blood sugar, cholesterol and a small reduction in weight and psychological tranquility. These effects will last if the lessons learned during Ramadan are carried after Ramadan is over.
Thus during Ramadan, I always feel better, have more energy, I sleep less and work more. I pray more and read more of the Quran. I check my blood pressure, blood sugar and cholesterol before and after Ramadan and they are always lower at the end.
Fasting is a special act of worship which is only between humans and God since no one else knows for sure if this person is actually fasting. Thus God says in hadith qudsi that "Fasting is for Me and I only will reward it". In another hadith, the Prophet Mohammad (peace be upon him) has said "If one does not give up falsehoods in words and actions, God has no need of him giving up food and drink".