All praise are due to Allah, who enrolled the Siam for the human being. During the rest eleven month without Ramadan, fat gathers in the human bodies.Siam breaks this fat and do fitness for the faster.It controlled debating and fat.
The Siam/Ramadan is one of the pillar of Islam,. As Allah says in the Holly Quran
يا ايها الذين امنوا كتب عليكم الصيام كما كتب على الذين من قبلكم لعلكم تتقون

(Sura al Bakara-182)
O  Believer , the fast has been made obligatory on you just as it was prescribed for the folloewer
of the Prophets before you.It is expected that this will produce piety in you.

what is Siam/Ramadan?
  According to the description of the Shariah, from the very beginning of the Sub ha Sadeck
to leave  eating, drinking, ill spoken of other, sexual function and forbidden work is call Siam.
Merit of Siam:  

1.  Siam habituated man to Allah's quality. 
2. Makes a man pious.
3. Create negligence about illegal income and expect.
4. Control insulin and Sugar.
5. Decay the fat.
6. Teaches to fell hunger pain of a hungry man. 

As a Bengali poet said
                               " Ever happy man never understand
                                           Sorrow of hunger,
                                  Never know pain of snake
                                           didn't bit."