I have 2 questions for ramadhan can u help?

ramadhan mubarak and aslamoalikom i have 2 questions if i fast can i lose weight in a good way and can u tell me why dont all muslims start fast in the same time with mecca if mecca are fasting then why arent we not fasting we should all fast when mecca fast and celebrate eid with mecca and can u take days of college when in ramadhan