The “drink more water” message is everywhere – water bottles are practically a fashion accessory – but when it comes to water, is more really… more?
The scientific evidence behind the ‘eight glasses a day’ isn’t actually all that compelling – Heinz Valtin, MD, puts it rather eloquently, “Despite the seemingly ubiquitous admonition to “drink at least eight 8-oz glasses of water a day” rigorous proof for this counsel appears to be lacking”1. Not a single study indicates that normal, healthy people require the suggested 8 glasses (2 litres) of water a day2, indeed it’s unclear where such a blanket recommendation even came from. Furthermore, studies show that there is no legitimate evidence that water ‘flushes toxins’, aids weight loss or even helps the skin3. Of course, and lest the message of this article be misconstrued, it’s not that water is bad for you, it’s just that it’s a bit of an urban myth that we need quite so much to keep well-hydrated.
Glucose (C6H12O6) + oxygen (6O2) → energy + carbon dioxide (6CO2) + water (6H2O)
Cellular respiration, where glucose is burned for energy (as above), produces byproducts of carbon dioxide and water. That is to say, each and every cell in your body produces water, each and every day. We need water, absolutely, but it’s not true that the water we drink (or eat, in food) is the only way by which our bodies remain hydrated.
Adequate salt and glucose are also needed for hydration, not just plain water alone. Too much water alone can cause cells to become overhydrated and swell, which is particularly dangerous for brain cells. Traditionally, remedies such as salted, sugared water, salted rice water, coconut juice and carrot soup (ie fluid + salt + glucose) were recommended for cases of dehydration. Hyponatremia (low sodium status) is a serious concern in the case of over-hydration with plain water, especially in people who are actively avoiding sodium in their diet (see this post about the importance of adequate salt).
The thing is, there’s nothing magical about a glass of water as opposed to fluid from any other food or beverage. Almost all foods contain some water and can contribute to our daily water intake, for example:
Melons are 80-92% water
Eggs are 74% water
Potatoes are 75% water
Cheese is 40-70% water
Beef is 60-70% water
Fresh fruits are naturally packed with water along with glucose and potassium, which is an essential electrolyte also lost daily through sweat and urination. Water- and nutrient-rich fruits, vegetables and other foods may be a superior source of hydration than just plain water, and a well-balanced diet means that the recommended ‘8 glasses a day’ is just overkill.
So, how much water do we really need?
There is no universal requirement for water intake – gender, height and weight and metabolic rate play significant roles. If you’re consuming lots of water-rich fruits and vegetables, you’ll need less than if you’re living on lots of nuts and processed grains. If you live in a hot, humid or high-altitude climate, your requirements will be much higher. Also, people who imbibe, particularly wine and spirits, should be aware that the alcohol is dehydrating, and a glass of water before and after alcohol can’t hurt fluid intake or the chances of avoiding a headache the next day.
Athletes will certainly have increased water needs post-exercise (and will also require more glucose, sodium and other electrolytes), however for your average Joe Bloggs, a glass of water with a little added sea salt along with a piece of fruit will probably suffice for rehydration after a sweat session.
For coffee-lovers, it’s worth noting that research has well and truly shown that caffeine is not dehydrating – your daily coffee actually contributes to your fluid intake, rather than increasing water requirements as is commonly assumed4.
As a guide, your urine should not be colourless (a sign of over-hydration), nor should it be too yellow. Excessive thirst can be a symptom of hyperglycemia among other conditions (without being an indication of dehydration), so if you’re experiencing a thirst that truly can’t be quenched, consult your doctor. Also, if you’re chugging whole glasses of water all at once without consuming adequate salt and glucose, you’re not really going to be hydrating your cells but simply diluting your urine5. Sip slowly and frequently for better effect.
The take-home message? Don’t go lapping up all the hydration hype and needlessly forcing yourself to drink copious amounts of water in the name of good health. Most people, believe it or not, do pretty well to just drink when they’re thirsty.
Glucose (C6H12O6) + oxygen (6O2) → energy + carbon dioxide (6CO2) + water (6H2O)
Cellular respiration, where glucose is burned for energy (as above), produces byproducts of carbon dioxide and water. That is to say, each and every cell in your body produces water, each and every day. We need water, absolutely, but it’s not true that the water we drink (or eat, in food) is the only way by which our bodies remain hydrated.
Adequate salt and glucose are also needed for hydration, not just plain water alone. Too much water alone can cause cells to become overhydrated and swell, which is particularly dangerous for brain cells. Traditionally, remedies such as salted, sugared water, salted rice water, coconut juice and carrot soup (ie fluid + salt + glucose) were recommended for cases of dehydration. Hyponatremia (low sodium status) is a serious concern in the case of over-hydration with plain water, especially in people who are actively avoiding sodium in their diet (see this post about the importance of adequate salt).
The thing is, there’s nothing magical about a glass of water as opposed to fluid from any other food or beverage. Almost all foods contain some water and can contribute to our daily water intake, for example:
Melons are 80-92% water
Eggs are 74% water
Potatoes are 75% water
Cheese is 40-70% water
Beef is 60-70% water
Fresh fruits are naturally packed with water along with glucose and potassium, which is an essential electrolyte also lost daily through sweat and urination. Water- and nutrient-rich fruits, vegetables and other foods may be a superior source of hydration than just plain water, and a well-balanced diet means that the recommended ‘8 glasses a day’ is just overkill.
So, how much water do we really need?
There is no universal requirement for water intake – gender, height and weight and metabolic rate play significant roles. If you’re consuming lots of water-rich fruits and vegetables, you’ll need less than if you’re living on lots of nuts and processed grains. If you live in a hot, humid or high-altitude climate, your requirements will be much higher. Also, people who imbibe, particularly wine and spirits, should be aware that the alcohol is dehydrating, and a glass of water before and after alcohol can’t hurt fluid intake or the chances of avoiding a headache the next day.
Athletes will certainly have increased water needs post-exercise (and will also require more glucose, sodium and other electrolytes), however for your average Joe Bloggs, a glass of water with a little added sea salt along with a piece of fruit will probably suffice for rehydration after a sweat session.
For coffee-lovers, it’s worth noting that research has well and truly shown that caffeine is not dehydrating – your daily coffee actually contributes to your fluid intake, rather than increasing water requirements as is commonly assumed4.
As a guide, your urine should not be colourless (a sign of over-hydration), nor should it be too yellow. Excessive thirst can be a symptom of hyperglycemia among other conditions (without being an indication of dehydration), so if you’re experiencing a thirst that truly can’t be quenched, consult your doctor. Also, if you’re chugging whole glasses of water all at once without consuming adequate salt and glucose, you’re not really going to be hydrating your cells but simply diluting your urine5. Sip slowly and frequently for better effect.
The take-home message? Don’t go lapping up all the hydration hype and needlessly forcing yourself to drink copious amounts of water in the name of good health. Most people, believe it or not, do pretty well to just drink when they’re thirsty.
