Millions of Muslims all around the world are abstaining from food and drink as they fast from sunrise to sunset in the month of Ramadan.
The Muslim holy book, the Quran, was revealed in Ramadan, making it the most sacred month in the Islamic calendar.
Fasting in the month of Ramadan is the third of Islam's five pillars.
In some parts of the world, the fasting period in a day can be up to 21 hours long. So what effect does that have on the human body?
TRT World 's Hasan Abdullah tries to find out.