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Where Did the 8 Glasses of Water A Day Myth Come From?

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By Chris Gayomali

We have all been told at some point that proper hydration requires us to consume eight glasses of water a day. That works out to about two liters, which is an awful lot of fluid, considering the average human stomach (when unexpanded) is about the size of a balled fist.

But health researchers have refuted the eight-glasses-a-day claim as a silly myth riding a wave of flimsy scientific literature. In fact, many of the groups behind the public push for over-hydration have been exposed as having — surprise! — monetary interests in the fluid industry.

For example: In a 2011 article published in the British Medical Journal, Margaret McCartney debunked the eight glasses a day myth and noted that one water advocacy group in Europe, Hydration for Health, is not only sponsored by, but was actually created by food giant Danone. Under the company's expansive culinary umbrella? Volvic, Evian, and Badoit bottled waters.

Set aside the entangled interests of Big Bottled Water, and you'll see that study after study continues to show that the human body is remarkably resilient when it comes to quenching our thirst. Saharan nomads, for example, are capable of subsisting on very little water for days at a time in one of Earth's most hellish climates, as was first noted in 1976 by anthropologist Claude Paque.

You and I, on the other hand, may get a bit cranky in our air-conditioned offices if we forget to visit the water cooler for a morning, but it's highly, highly, highly improbable that we'd shrivel and die at the dusty hands of the dehydration monster. Consider all the other stuff we consume. Despite the widely held notion that tea and coffee dehydrate us, they actually count toward our overall water intake, says Dr. Stanley Goldfarb, a nephrologist (kidney researcher) at the University of Pennsylvania. Even though we're told it's important to drink eight glasses of water a day, "there's no evidence that benefits health in any real way and it really represents an urban myth," says Goldfarb. Even something like, say, a baked potato, is 75 percent water.

So where exactly did this eight glasses of water a day voodoo come from? The very idea of a "minimal water requirement" is actually a fairly recent notion that first appeared in dietary guidelines published in 1945 by the Food and Nutrition Board of the National Academy of Sciences. The academy spuriously suggested that "2,500 mL [2.5 liter] of fluid should be ingested on a daily basis," although a primary clinical study was never actually cited.

The idea may have been at least partly put forth by Frederick J. Stare, an influential 20th century nutritionist and founding chairman of the department of nutrition at the Harvard School of Public Health. (He passed away in 2002 at age 91.) Stare was one of the first to recommend that humans consume six or so 12-ounce glasses of water a day.

Since then, researchers have begun to see eight glasses a day as an overestimate (especially considering our diets), but there are still advocates pushing for eight glasses of pure water or more. Those proponents include Dr. Fereydoon Batmanghelidi, a medical practitioner in Virginia who claims that a lack of water is responsible for many preventable diseases. Water, after all, is still good for us. Recent studies have suggested that adequate hydration may not only give our cognition a boost, but goes a long way toward keeping chronic kidney disease at bay.

As for how much we should be drinking, there is unfortunately no hard and fast rule. (Sorry!) And when you include all the other stuff we munch on or guzzle throughout the day, we actually consume more than the recommended two liters. A 1995 Australian survey found that the diet of average adults provides more than enough daily fluid: Women take in about 2.8 liters a day, and men consume 3.4 liters a day.

Research suggests that drinking water when you start to feel thirsty is sufficient should you desire to continue existing. Clearly, it's all relative, as when you feel thirsty will be different if you're drenching yourself in spin class or spinning in your cushy chair at work. As with most things, it's probably best to listen to your body before proceeding accordingly.

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What Happens When You Flush an Airplane Toilet?
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For millions of people, summer means an opportunity to hop on a plane and experience new and exciting sights, cultures, and food. It also means getting packed into a giant commercial aircraft and then wondering if you can make it to your next layover without submitting to the anxiety of using the onboard bathroom.

Roughly the size of an apartment pantry, these narrow facilities barely accommodate your outstretched knees; turbulence can make expelling waste a harrowing nightmare. Once you’ve successfully managed to complete the task and flush, what happens next?

Unlike our home toilets, planes can’t rely on water tanks to create passive suction to draw waste from the bowl. In addition to the expense of hauling hundreds of gallons of water, it’s impractical to leave standing water in an environment that shakes its contents like a snow globe. Originally, planes used an electronic pump system that moved waste along with a deodorizing liquid called Anotec. That method worked, but carrying the Anotec was undesirable for the same reasons as storing water: It raised fuel costs and added weight to the aircraft that could have been allocated for passengers. (Not surprisingly, airlines prefer to transport paying customers over blobs of poop.)

Beginning in the 1980s, planes used a pneumatic vacuum to suck liquids and solids down and away from the fixture. Once you hit the flush button, a valve at the bottom of the toilet opens, allowing the vacuum to siphon the contents out. (A nonstick coating similar to Teflon reduces the odds of any residue.) It travels to a storage tank near the back of the plane at high speeds, ready for ground crews to drain it once the airplane lands. The tank is then flushed out using a disinfectant.

If you’re also curious about timing your bathroom visit to avoid people waiting in line while you void, flight attendants say the best time to go is right after the captain turns off the seat belt sign and before drink service begins.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Why is Friday the 13th Considered Unlucky?
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Today, people around the globe will feel uneasy about getting out of bed, leaving their homes, or going about their normal daily routines, all because of a superstition. These unfortunate folks suffer from paraskavedekatriaphobia, a common neurosis familiar to us all: the fear of Friday the 13th. But just where did this superstitious association come from, and how did it catch on?

The truth is that no one is absolutely sure where the idea that Friday the 13th is unlucky originated. Donald Dossey, the founder of the Stress Management Center and Phobia Institute in Asheville, North Carolina, suspects the fear can be traced back to a Norse myth about 12 gods who had a dinner at Valhalla—the fabled hall where legendary Norse heroes feasted for eternity after they died—that was interrupted by a 13th guest, the evil and mischievous god Loki.

According to legend, Loki tricked Höðr (the blind god of winter and son of Odin, the supreme god in Norse mythology) into shooting his brother Baldr (the benevolent god of summer who was also a son of Odin) with a magical spear tipped with mistletoe—the only substance that could defeat him. Thus the number 13 was branded as unlucky because of the ominous period of mourning following the loss of such powerful gods by this unwanted 13th guest.

For whatever reason, among many cultures, the number 12 emerged throughout history as a "complete" number: There are 12 months in a year, 12 signs of the zodiac, 12 Gods of Olympus, 12 sons of Odin, 12 labors of Hercules, 12 Jyotirlingas or Hindu shrines where Shiva is worshipped, 12 successors of Muhammad in Shia Islam, and 12 tribes of Israel. In Christianity, Jesus was betrayed by one of his 12 Apostles—Judas—who was the 13th guest to arrive for the Last Supper. Surpassing the number 12 ostensibly unbalances the ideal nature of things; because it is seen as irregular and disrespectful of a sense of perfection, the number 13 bears the stigma of misfortune and bad luck we know today.

WHY FRIDAY?

Friday joins in the mix mostly because all of the early accounts of Jesus’s crucifixion agree that it took place on Friday—the standard day for crucifixions in Rome. As Chaucer noted in The Canterbury Tales, "And on a Friday fell all this mischance." Yet perpetuating Friday as an unlucky day in America came from the late 19th-century American tradition of holding all executions on Fridays; Friday the 13th became the unluckiest of days simply because it combined two distinct superstitions into one. According to the Oxford University Press Dictionary of Superstitions, the first reference to Friday the 13th itself wasn’t until 1913. (So despite actually occurring on Friday, October 13, 1307, the popular notion that the Friday the 13th stigma comes from the date on which the famed order of the Knights Templar were wiped out by King Philip of France is just a coincidence.)

The repercussions of these phobias reverberated through American culture, particularly in the 20th century. Most skyscrapers and hotels lack a 13th floor, which specifically comes from the tendency in the early 1900s for buildings in New York City to omit the unlucky number (though the Empire State Building has a 13th floor). Some street addresses also skip from 12 to 14, while airports may skip the 13th gate. Allegedly, the popular Friday the 13th films were so-named just to cash in on this menacing date recognition, not because the filmmakers actually believed the date to be unlucky.

So, is Friday the 13th actually unlucky? Despite centuries of superstitious behavior, it largely seems like psychological mumbo jumbo. One 1993 study seemed to reveal that, statistically speaking, Friday the 13th is unlucky, but the study's authors told LiveScience that though the data was accurate, "the paper was just a bit of fun and not to be taken seriously." Other studies have shown no correlation between things like increased accidents or injuries and Friday the 13th.

And Friday the 13th isn't a big deal in other cultures, which have their own unlucky days: Greeks and Spanish-speaking countries consider Tuesday the 13th to be the unluckiest day, while Italians steer clear of Friday the 17th. So today, try to rest a little easy—Friday the 13th may not be so unlucky after all.

Additional Source: 13: The Story of the World’s Most Popular Superstition.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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