Even Muslims without serious health issues can find fasting during Ramadan, which started on Monday, a challenge as the body adjusts to going without any form of food or drink between dawn and dusk for a lunar month.

"For someone who is used to eating several meals a day and then you go to a long period between sunrise to sundown where you can't eat, that creates a whole new dynamic for your metabolism," said Dr. Memoona Hasnain, director of family medicine research at the University of Illinois at Chicago.

Though medical studies have not shown any serious adverse effects of the Ramadan fasting schedule upon healthy Muslims, doctors said they have seen patients suffer lack of sleep from waking up early for the traditional pre-dawn meal, called sahur, after staying up late for nighttime prayers and ceremonies. And counterintuitively, doctors said many of their patients actually gain weight during the fasting month.

"When you are hungry, you feel like you want to eat everything and anything," said Dr. Mohammed Zaher Sahloul.

To prevent weight gain and minimize hunger, experts recommend that Muslims eat a sahur rich with complex carbohydrates such as whole-wheat bread, and break their fast with sugar-rich food or juices.