It's bad enough that these guys have to play in the Amazon. The weather in Brazil is so preposterously hot and humid that FIFA instituted cooling breaks so players wouldn't keel over and die during games. But what are the World Cup's Muslim players supposed to do now that Ramadan is here? The month-long religious fast—which lasts from Saturday, June 28th through the evening of Monday, July 28—puts some of the game's top players in a difficult, potentially dangerous situation, possibly more so at Brazil's World Cup than in other pro sports settings.

In addition to abstaining from eating and drinking, observant Muslims are also supposed to refrain from smoking and sexual relations from dawn to sunset.1 But those fall more or less in line with what a lot of teams require anyway. The decision to fast, though, won't just affect one or two guys. Three players on Belgium's squad—Marouane Fellaini, Adnan Januzaj and Eden Hazard—as well as France's Karim Benzema and Paul Pogba could potentially be affected. Others, like Germany's Mesut Ozil will make exceptions for the World Cup.2 (Algeria's team, made up exclusively of Muslim players, reportedly received an exemption before Monday's loss to Germany; their coach said fasting was a ''private issue and players will do exactly as they wish.'') It's the first time in twenty-eight years that the religious fast overlaps with the World Cup—the last time it happened was in Mexico in 1986—and nobody really knows what to expect. So just how dangerous is it to play soccer while observing Ramadan?

Most of our knowledge comes by way of anecdotal reports from athletes in other sports, like Hakeem Olajuwon, who claimed his basketball game actually improved when he fasted. But it turns out there are a handful of studies examining how Ramadan affects soccer players, and the results are fascinating.

In one study, players from two Algerian professional soccer teams were put through a series of mental and physical tests before and after Ramadan. Players were asked about all kinds of things—from sleeping habits to the quality of their workouts—and they were asked to evaluate match performance.


Researchers found that foot speed, agility, dribbling speed, and endurance all declined significantly during Ramadan, which supports findings from a number of other studies showing that both aerobic and anaerobic activity diminish while fasting. Interestingly, nearly 70% of the Algerian players thought that their training and match performance were adversely affected during the month-long fast, which led investigators to speculate that Ramadan was affecting both performance and mood. These guys weren't playing as well and they knew it.

This isn't something that's really talked about, and with good reason. The annual observance of Ramadan is one of the Five Pillars of Islam. The act of fasting is said to cleanse the soul by freeing it from harmful impurities while teaching observers how to better practice self-discipline and sacrifice. It's not exactly the ideal time to complain about soccer performance. But fasting unquestionably alters both the body and mind of elite athletes.

Studies also show that in addition to altering mood, people have more trouble performing mental activities during Ramadan because they're less alert. (This may explain the high incidence of traffic accidents during the month). A recent study tried to explain this surprisingly complex phenomenon by examining sleep-wake patterns in soccer players who were fasting. Researchers discovered that athletes sleep nearly ninety minutes less per night during Ramadan. It's unclear precisely why this happens but it appears that hunger makes circadian rhythms go haywire.


For most species (including ours) food availability and hibernation are intricately intertwined. Altering the former will influence the latter. When food consumption is inconsistent, the body switches into a mode that requires less sleep, so it can, in theory, spend more time hunting for calories. It's an animal instinct, largely out of our control, and it's remarkably beneficial to most species, just not the one that skips a meal to play soccer. So fasting soccer players are not only thirsty, hungry, and moody, they're also exhausted.

These fasting issues are intriguing, but ultimately far less concerning than the potential for life-threatening dehydration while playing in Brazil's oppressive heat and humidity. If a player is unable to adequately hydrate during vigorous exercise, he can develop dangerous fluctuations in blood sodium levels, resulting in a potentially lethal condition called hypernatremia.3 In just a few hours an overheated athlete without access to water can develop hypernatremia, lose consciousness, and slip into a coma. (In my practice, I typically encounter this nightmare scenario in elderly or disabled patients who are unable to take in water as their thirst dictates).

All of this makes one thing clear: It's remarkably dangerous to compete at an elite level in sweltering heat without access to food or water, but people have done it and will continue to do it. We don't know how many World Cup players are currently fasting—most haven't announced their plans—but it's considered obligatory for adult Muslims during Ramadan, except those who are suffering from an illness, traveling, pregnant, breastfeeding, diabetic, or menstruating. As a physician, I can't help but wish "playing soccer in the Amazon" could be added to that list.


1The word Ramadan is derived from the Arabic root ramiḍa or ar-ramaḍ, which means scorching heat or dryness. In some Muslim countries, failing to fast, or, eating and drinking in public during the days of Ramadan are considered crimes.

2Some players have declared they won't fast during the World Cup. Ozil said he won't take part in Ramadan because he "is working."


3I've previously written about how a fluid imbalance throws sodium concentration out of whack and can cause the brain to shrink or swell.

Matt McCarthy is an assistant professor of medicine at Weill Cornell Medical College in Manhattan. You can follow him on Twitter here.