CLOSE
ThinkStock
ThinkStock

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

ThinkStock
ThinkStock

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.

More from The Week...

A Linguistic Dissection of our Affect/Effect Problem

*

12 Things We Know About How the Brain Works

*

Silence is Golden. It Can Also Drive You Crazy

nextArticle.image_alt|e
iStock
arrow
Big Questions
Do Bacteria Have Bacteria?
iStock
iStock

Drew Smith:

Do bacteria have bacteria? Yes.

We know that bacteria range in size from 0.2 micrometers to nearly one millimeter. That’s more than a thousand-fold difference, easily enough to accommodate a small bacterium inside a larger one.

Nothing forbids bacteria from invading other bacteria, and in biology, that which is not forbidden is inevitable.

We have at least one example: Like many mealybugs, Planococcus citri has a bacterial endosymbiont, in this case the β-proteobacterium Tremblaya princeps. And this endosymbiont in turn has the γ-proteobacterium Moranella endobia living inside it. See for yourself:

Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)
Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)

I don’t know of examples of free-living bacteria hosting other bacteria within them, but that reflects either my ignorance or the likelihood that we haven’t looked hard enough for them. I’m sure they are out there.

Most (not all) scientists studying the origin of eukaryotic cells believe that they are descended from Archaea.

All scientists accept that the mitochondria which live inside eukaryotic cells are descendants of invasive alpha-proteobacteria. What’s not clear is whether archeal cells became eukaryotic in nature—that is, acquired internal membranes and transport systems—before or after acquiring mitochondria. The two scenarios can be sketched out like this:


The two hypotheses on the origin of eukaryotes:

(A) Archaezoan hypothesis.

(B) Symbiotic hypothesis.

The shapes within the eukaryotic cell denote the nucleus, the endomembrane system, and the cytoskeleton. The irregular gray shape denotes a putative wall-less archaeon that could have been the host of the alpha-proteobacterial endosymbiont, whereas the oblong red shape denotes a typical archaeon with a cell wall. A: archaea; B: bacteria; E: eukaryote; LUCA: last universal common ancestor of cellular life forms; LECA: last eukaryotic common ancestor; E-arch: putative archaezoan (primitive amitochondrial eukaryote); E-mit: primitive mitochondrial eukaryote; alpha:alpha-proteobacterium, ancestor of the mitochondrion.

The Archaezoan hypothesis has been given a bit of a boost by the discovery of Lokiarcheota. This complex Archaean has genes for phagocytosis, intracellular membrane formation and intracellular transport and signaling—hallmark activities of eukaryotic cells. The Lokiarcheotan genes are clearly related to eukaryotic genes, indicating a common origin.

Bacteria-within-bacteria is not only not a crazy idea, it probably accounts for the origin of Eucarya, and thus our own species.

We don’t know how common this arrangement is—we mostly study bacteria these days by sequencing their DNA. This is great for detecting uncultivatable species (which are 99 percent of them), but doesn’t tell us whether they are free-living or are some kind of symbiont. For that, someone would have to spend a lot of time prepping environmental samples for close examination by microscopic methods, a tedious project indeed. But one well worth doing, as it may shed more light on the history of life—which is often a history of conflict turned to cooperation. That’s a story which never gets old or stale.

This post originally appeared on Quora. Click here to view.

nextArticle.image_alt|e
iStock
arrow
Big Questions
Why Do Cats 'Blep'?
iStock
iStock

As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
iStock

If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

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

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios