Fact or Fiction? You Must Drink 8 Glasses of Water Daily

    Do healthy people really need liquids even when they are not thirsty?

    Virtually every health-conscious person can quote the recommendation: Drink at least eight eight-ounce glasses of water per day. Other beverages-coffee, tea, soda, beer, even orange juice-don't count. Watermelon? Not a chance.

    There's no denying that water is good for you, but does everyone really need to drink 64 ounces or more every day? According to Heinz Valtin, a retired professor of physiology from Dartmouth Medical School who specialized in kidney research and spent 45 years studying the biological system that keeps the water in our bodies in balance, the answer is no.

    Valtin says that for people who have specific health concerns, such as kidney stones or a tendency to develop urinary tract infections, drinking lots of water can be beneficial. But after an extensive search in 2002 for the origins of what is commonly referred to as the "8 x 8" guideline and a review of associated health claims, he reports finding no scientific evidence supporting the notion that healthy individuals need to consume large quantities of water. In 2008 Dan Negoianu and Stanley Goldfarb reviewed the evidence for the Journal of the American Society of Nephrology. They came to a similar conclusion: "There is no clear evidence of benefit from drinking increased amounts of water."

    In fact, Valtin found that the 8 x 8 guideline may have originated from a misunderstanding. In 1945 the Food and Nutrition Board, now part of the National Academy of Sciences's Institute of Medicine, suggested that a person consume one milliliter of water （about one fifth of a teaspoon） for each calorie of food. The math is pretty simple: A daily diet of around 1,900 calories would dictate the consumption of 1,900 milliliters of water, an amount remarkably close to 64 ounces. But many dieticians and other people failed to notice a critical point: namely, that much of the daily need for water could be met by the water content found in food.

    The Board revisited the question of water consumption in 2004. Its panel on "dietary preference intakes for electrolytes and water" noted that women who appear adequately hydrated consume about 91 ounces （2.7 liters） of water a day and men about 125 ounces （3.7 liters）. These seemingly large quantities come from a variety of sources-including coffee, tea, milk, soda, juice, fruits, vegetables and other foods. Instead of recommending how much extra water a person should drink to maintain health, the panel simply concluded that "the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide."

    真實的謊言：一天必須喝八杯水嗎？

    健康人即使不口渴也需要補充水分嗎？

    幾乎每個關(guān)注健康的人都知道這樣一條建議：每天至少飲八大杯8盎司玻璃杯的水。其它飲料，諸如咖啡 ,茶，蘇打水，啤酒，甚至橙汁 還不計算在內(nèi)。西瓜就更不包括了。

    水確實對人有益。但人們真的每天需要喝至少六十四盎司的水？生理學(xué)專家海因茨。瓦爾汀認為情況并非如此。這位特茅斯醫(yī)學(xué)院的退休教授專門從事腎臟研究，花了45年時間研究人體生物系統(tǒng)，看我們身體內(nèi)的水分如何保持平衡。

    瓦爾汀認為，對于患腎結(jié)石或者可能尿路感染，確實擔心身體健康的人來說，多喝水有好處。但是在2002年對所謂" 8 × 8 "準則的源頭經(jīng)過廣泛的追索和對健康產(chǎn)生影響的提法仔細審查后，他認定健康人也需要多喝水的提法缺乏科學(xué)依據(jù)。2008年丹。 尼戈亞盧（Negoianu）及史坦利。戈德法布在美國腎病學(xué)會 發(fā)表了對有關(guān)證據(jù)的評論。他們得出了類似的結(jié)論： "沒有確切證據(jù)證明多喝水有利健康。 "

    事實上，瓦爾汀發(fā)現(xiàn)， 8 × 8準則可能源于一種誤解。1945年，食品和營養(yǎng)委員會（現(xiàn)在是美國國家科學(xué)院下屬的醫(yī)學(xué)研究所的一部分）提出，一個人消費一卡路里的食物需要1毫升的水（約五分之一茶匙）.很簡單可以算出：一天吃飯吸收約1900卡路里意味著要引用1900毫升水，剛好等于64盎司。但許多營養(yǎng)師和有關(guān)人士忽略了一個關(guān)鍵點，即：人體每天所需的水分大多可由食物自身含有的水提供。

    該委員會2004年重新審視了人體攝入水分的問題。其小組關(guān)于"飲食偏好攝入的電解質(zhì)和水"指出，女性雖然看起來更"水靈",她們每天需要攝入約91盎司（ 2.7公升）的水，而男子每天約125盎司（ 3.7公升） .這些看似大量的水分其實來源廣泛，包括咖啡，茶，牛奶，汽水，果汁，水果，蔬菜和其他食品。該小組并沒有建議應(yīng)該額外引用多少水才能保持健康，而是認為 "絕大多數(shù)的健康人感覺口渴才去喝水就足以充分滿足他們的每天的水需求。 "