If I had to nominate one pervasive myth in nutrition, it would be the popular advice that we should drink at least eight glasses of water a day. Of course our bodies need water, otherwise we would die from dehydration. But the amount needed is extremely variable and depends on a person’s body size, physical activity levels, climate and what types of food they are eating.
Water makes up about 60% of an adult’s body weight and is an essential nutrient, more important to life than any others. Water helps regulate body temperature, carries nutrients and waste products throughout the body, is involved in blood transport, and allows many metabolic reactions to occur. It also acts as a lubricant and cushion around joints, and forms the amniotic sac surrounding a foetus.
It is believed that the “eight glasses” myth was a US Recommended Dietary Allowance dating back to 1945. The guide said a suitable allowance of water for adults was 2.5 litres a day, but most of this water could be found in prepared foods. If that last, crucial part is ignored, the statement could be interpreted as clear instructions to drink eight glasses of water a day.
Even a comprehensive search of the scientific literature finds no evidence to support the eight-glasses-a-day advice. The clear reason that evidence for such prescriptive advice doesn’t exist is that a person can get all the water they need without consuming a single glass.
Drinks like soft drink, fruit juice, tea and coffee, milk, and foods like fruit, yoghurt, soups, and stews all have appreciable amounts of water that contribute to fluid intake.
Australian dietary recommendations also bust the eight-glass myth as the official Nutrient Reference Values state “there is no single level of water intake that would ensure adequate hydration and optimal health for the apparently healthy people in the population.”
Don’t be concerned about seeing coffee listed as a fluid – the “coffee makes you dehydrated” mantra is another myth that needs to be busted. Drinks such as coffee, tea and cola do have a mild diuretic effect from the caffeine but the water loss caused by this is far less than the amount of fluid consumed in the drink in the first place. It’s only alcoholic drinks which have a dehydrating effect.
So how do you know if you are drinking enough water? Well. You can check this for yourself every few hours. If your urine is lightly coloured or clear, you’re drinking enough. If it’s dark, then you should drink more. How simple is that?
Young and waterlogged says
March 25, 2015 at 2:29 amAs a newcomer to this website (first visit tonight!), I’m interested in diverse views on nutrition and health and would have found Peter’s perspective of value had he delivered it with goodwill. Instead, his comments serve to paint him as arrogant, pontificating, and mean-spirited, obfuscating the actual message. Pity, as he sounds intelligent and likely had something useful to offer, but for me, the tone was louder than the content!
On a more relevant note, I’m curious about the impact of my 2-3 litres of hot water intake a day. It’s been a habit of mine for many years now, though found I had to add electrolytes when sweating profusely (such as dancing for hours!). As I age, I wonder whether I’m doing more harm than good. I have great skin and look younger than my years (to which I credit genes and yes, the water to some degree!), but I have poor health. I do keep an eye on the colour of my urine, which is predictably pale generally. Is it likely to be negatively impacting my health to continue drinking this amount of water?
Tim Crowe says
March 25, 2015 at 6:52 amThank you for your comments. Interesting that you choose to drink warm water, but then again, this shouldn’t be any reason why it would be better or worse for a person as will be quickly equilibrated to 37 C in the body and hot tea/coffee are very common drinks for most people. The basis of adding electrolytes to drinks may assist some losses through sweat and is the basis of adding these to sports drinks (as too to improve glucose absorption). On hydration, urine colour is certainly a valid method to assess hydration on a day-to-day basis and is why there are charts such as this http://www.continencevictoria.org.au/sites/default/files/UrineColourChart.pdf produced by health organisations.
Peter says
March 19, 2015 at 10:39 pmI had some chuckles reading this one Tim.
You say: “Drinks such as coffee, tea and cola do have a mild diuretic effect from the caffeine but the water loss caused by this is far less than the amount of fluid consumed in the drink in the first place. It’s only alcoholic drinks which have a dehydrating effect.” So by this reasoning we must conclude that if drinking, say 500 ml of beer, we will void greater than 500 ml as a result, thereby dehydrating (whereas caffeinated beverages being mild leave us with a nett positive fluid gain). Funny.
And this: “So how do you know if you are drinking enough water? Well. You can check this for yourself every few hours. If your urine is lightly coloured or clear, you’re drinking enough. If it’s dark, then you should drink more. How simple is that?” Well, interestingly, both too simple and yet, not simple enough. First, it is too simple because lots of things can darken urine besides dehydration. Also, confounding lightly-coloured vs. dark with clear vs. dark just confuses the issue. Colour and clarity can each point to different issues. It is more significant that the person is actually voiding “every few hours” when it comes to your simple assessment. Second, it is too complex because you overlooked the most significant factor: thirst!
However, I stopped chuckling when I read your misinformation to Jared. Your analogous reference to infants and breast milk is entirely disingenuous. You should understand the marked differences between the digestive functions of breast-fed infants and adults consuming solid foods. You only get worse when you dismiss as “total rubbish” something of real clinical significance and something you as a scientist ought to understand. I think you have gone a little too far in your quest for fame as a myth-buster. You appear to be making up some of your own.
Maybe your limited clinical practice opportunities as a dietitian and perhaps your youth have limited your understanding. From late middle-age onward even otherwise healthy people have significantly less gastric acid and effective digestion becomes a challenge. Even simple chemistry should tell you that a diluted acid will be less effective. You need to learn to be far more careful in your pontifications about health, provide more details and qualifications, and avoid making grandiose statements. We have enough trouble dealing with misinformation without it also coming from sources people would consider credible. So come on Tim, you can do better.
Tim Crowe says
March 21, 2015 at 1:28 pmThank you for your comments, I believe you’ve misunderstood what I wrote. The diuretic effect of a given dose of caffeine as normally found in coffee is much less than the volume of water it is contained in in a cup of coffee. While the diuretic effect of alcohol in a typical drink is greater than the volume of water it is contained in.
Tim says
November 2, 2015 at 7:42 amPeter. Rude, dude.
Tim provided a rough guide countering a common trope.
His advice will work for most people, most of the time.
Peter - call 1300 6555 06 says
March 22, 2016 at 12:09 pmPeter for somebody so critical it might pay to learn how to read to understand. You missed so many points it’s not funny, yet you still felt the need to lay out this diatribe of ignorance.
Jared says
March 22, 2014 at 4:59 amTim,
You’ve got a point – “If your urine is lightly colored or clear, you’re drinking enough. If it’s dark, then you should drink more.”
I frequently hear things like – Don’t drink water just before eating / Don’t drink water while eating / Don’t drink water immediately after eating..
Are these just Myths or a Fact?
Tim Crowe says
March 25, 2014 at 8:44 amThanks for your comments Jared – yes, all that you’ve read about ‘not drinking water before/during/after’ eating is total rubbish as all linked to some strange theory that the water will affect digestion. If that was the case, infants would die of malnutrition as breast milk is 90% water and we could get little nutrition from foods with a high water content such as fruits. Water/fluid is needed as part of digestion and also has little effect on diluting any of the digestive enzymes or altering the pH of the stomach.