More than 1.5 billion Muslims from around the world - almost a quarter of the population of the globe - were on Friday preparing to begin the fasting month of Ramadan, the most important of the Islamic calendar because it constitutes one of the five pillars of Islam.

During this month, Muslims who have reached puberty will not be able to eat, drink, smoke or have sex while the sun is on the horizon, and only menstruating and pregnant women, those with certain ailments and travelers who make a difficult journey, are exempt, although all must make up later for the missed days of fasting.

The exact hours of sunrise and sunset appear on phone screens now, but mosques continue to give timely reminders with their calls to the prayers of Fajr (sunrise) and Maghreb (sunset), while the great cities also use cannons or sirens to mark the anticipated moment of sunset.

In Muslim-majority countries, life is completely transformed during the month of fasting: businesses, public offices and schools shorten their schedules to make fasting quicker, while cafés and restaurants close during daylight hours and do their biggest business after sunset.

Paradoxically, the month of fasting is also the month in which there is a higher expenditure on food in households, and consumption indicators soar in this holy month, as well as the prices in shopping baskets.

There are very few countries that enforce fasting and punish the offender (Saudi Arabia, Bahrain, Pakistan, Afghanistan, Iran, Malaysia, Brunei and Morocco), but in most of the Muslim world Ramadan is fulfilled by will or by social pressure, and it is unusual to see a person breaking the fast in public.

The observance of fasting is one of the best thermometers to measure one's roots in the world of Islam, which is currently the fastest growing religion on a global level and one that grows in practice alongside belief.

A recent study by the prestigious Pew Research Center in the United States asked: "How much does Islam matter in your life?" and the results were overwhelming: more than 90 percent of respondents in Africa and Southeast Asia said that "it matters a lot," while the percentage was more than 80 percent in the Arab world and Turkey, and only dropped to 70 percent in the former Soviet republics.

The same study asked for more specific questions about observance, such as frequency of prayer, attendance at the mosque, reading the Qur'an, or handing over alms, and for of all of them fasting in Ramadan was by far the Islamic practice more respected among Muslims around the world.

Given the rapid population growth in the world's Muslim regions in Asia and Africa, it is estimated that Muslims will almost double their number in 2050 to 2.8 billion, which will then make them the leading religion in the world, ahead of Christianity.

If observance of the religion in Africa and Asia continues to grow, as has been occurring in recent decades, then by 2050, one in three humans will fast in Ramadan.