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Media Fail: Busting the Water “Myth” 

A few years ago an editorial in the Journal of the American Society of Nephrologyi started a flurry of media reports claiming that the widely accepted suggestion that one should drink 8 glasses of water a day was baseless—basically an urban myth.

The authors of the editorial concluded “nobody really knows” where the ‘8 x 8’ recommendation (64-ounce daily target) got started,ii and, “there is no single study—and therefor no single outcome—that has led to these recommendations.” The implication was that there is no wisdom behind drinking eight glasses of water a day. Really?

Did we just throw out the baby with the bath water? The short answer is yes! True there isn’t a specific study that the recommendation can be traced back to--but that's true for pretty much all nutrition guidelines! So, let us consider what we do know:

The latest Institute of Medicine (IOM) report on Water and Electrolytes (2004)iii (which "establishes nutrient recommendations on water, salt and potassium to maintain health and reduce chronic disease risk") designates an “adequate intake” (AI) for males (3.7 liters) and females (2.7 liters). These amounts are for total daily fluids (not exclusively water), and it’s expected that 20% of the value comes from food. (The IOM is part of the National Academy of Sciences, a nongovernment nonprofit science organization that addresses health and health care.)

The IOM AI (for the most part) simply balances what we naturally lose in fluid each day. A sedentary 150-pound man loses about 3 quarts of water daily, while a sedentary 120-pound woman loses about 2.5 quarts—through urine, sweat, stools, and evaporation. The full IOM report includes over 360 references including "water-balance" studies, and U.S. survey data (where the median fluid intake was an important end-point).

The IOM report notes that fluid requirements vary widely among individuals: individual fluid needs vary with body weight and gender, but also increase dramatically with activity level, increasing ambient temperatures, and with higher humidity levels. This tells us that active people, and those in warmer climates may have higher requirements than the AI, while folks who are sedentary, or live in colder climates may have lower requirements than the AI.

Long story short, however, is that the IOM recommendation for FLUID intake is not all that different than the seemingly discredited recommendation for “8 glasses of water a day” (although it need not be all from water).

In fact, the IOM AI guideline is actually higher—take a look (this is 80% of the AI, as 20% is expected to be taken in from food):

So how much water, and what else, should we be drinking? Aproposed guidance system” for beverage consumption was published in the American Journal of Clinical Nutrition in 2006ivauthored by six top research scientists in the nutrition field, including Harvard’s Walter Willett.

The recommendations from this group of experts are that the majority of our fluid intake be from water, unsweetened tea or coffee. They were cautious regarding artificially sweetened beverages, writing that, “FDA-approved noncaloric sweeteners are considered safe, although other than FDA surveillance data there is [actually] no evidence from long-term studies in humans… [regarding safety].”

Here’s their proposal to guide the American people on fluid intake. These categories add up to 98-fluid ounces/day (which is equivalent to 80% of the 3.7 liter IOM AI for men).

Level 1 — Water, 20-50 fluid oz/day.

Level 2 — Unsweetened tea and coffee, 0-40 fluid oz/day (can replace water, however caffeine is a limiting factor </= 400mg/day ~32 fluid oz coffee/day).

Level 3 — Low-fat or skim milk, and soy beverages, 0-16 fluid oz/day.

Level 4 — Artificially sweetened beverages, 0-32 fluid oz/day.

Level 5 — Caloric beverages with some nutrients, 0-8 fluid oz. 100% fruit juice/day, 0-1 alcoholic drink/day for women, and 0-2 alcoholic drinks/day for men (one drink = 12 fluid oz beer, 5 fluid oz wine, or 1.5 fluid oz distilled spirits), and 0 fluid oz of whole milk per day.

Level 6 — Calorically sweetened beverages, 0-8 fluid oz/day.

The bottom line:

  • The idea of getting 8 glasses of FLUIDS per day is not out of whack with expert guidance.

  • Water still reigns as the fluid of choice, while unsweetened tea and coffee are strong second-placers (they’re both rich in health-promoting antioxidants).

While I didn't cover the details today, adequate hydration has been shown to improve both cognitive and physical performance, and may be a factor in avoiding bladder and colorectal cancers and other health issues.

And finally, the IOM did not set an upper limit for fluid intake as problems from excess water intake are not generally seen in healthy people with the exception of endurance athletes (who need to drink electrolyte replacements, not just water). See more on "water intoxication" (hyponatremia) here.

All the Best!

Related: Is what you're drinking helping or hindering your weight loss efforts?


i Negoianu D., Goldfarb S. J Am Soc Nephrol 2008;19:1041-1043.

ii Valtin, H. Am J Physiol Regul Inegr Comp Physiol 2002;283:R993-R1004

Reader Comments (1)

In addition, fluid recommendations in nursing homes and for tube-fed patients are ~1ml per calorie. 2000 ml (for the "average" 2000 calorie intake) is pretty darn close to 8 cups a day!

October 31, 2012 | Unregistered CommenterLaurie Beebe, MS, RD, LD

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