Water: Why you should drink it, and how much you need

21 01 2013

35bytuI have received a few comments about the amount of water that I drink (3-4 L per day), and wanted to quickly touch on the subject of water. We all know that it’s important to drink water, but how much? And why is it so important? Hopefully this article will answer your questions!

 

Fast facts about water and the human body

Water makes up 60% of our total bodyweight.

Water is necessary for the transfer of proteins, as well as the transfer of nutrients into cells, and waste products away from cells.

Water lubricates our joints and acts as a shock-absorber for our eyes and spinal cord.

Water is critical in regulating body temperature.

Water is a very important source of minerals (fluoride, calcium, magnesium, etc).

The human body produces roughly 200-300 mL of usable water daily, and even more so in growth stages.

We get roughly 1 L of water daily from the foods we consume. More if you eat raw veggies and fruit, less if your diet is more processed.

Water loss

We lose water through a few different avenues:

– Through expired air and through evaporation (different than sweating) we lose roughly 650-850 mL daily

– Through sweating (caused by exercise and/or hot climates) we can lose several liters of water. The highest recorded rate ever is 3.7 L per hour. Insane.

– Through feces & urine we excrete, minimally, 400-500 mL per day- normal kidney function requires this basic amount. Again though, this is an absolute minimum, and the amount of water we ingest will increase the amount that we excrete.

What happens when we lose water?

Aside from the things we feel and the things that happen physically when we lose water (headaches, fatigue, thirst, dizziness, flushing, nausea, fainting), here is what happens to your body physiologically:

0.5% loss = Increased strain on the heart

1% loss = Reduced aerobic endurance

3% loss = Reduced muscular endurance

4% loss = Reduced muscle strength, reduced motor skills, heat cramps

5% loss = Heat exhaustion, cramping, fatigue, reduced mental capacity

6% loss = Physical exhaustion, heatstroke, coma

10-20% = DEATH

Most people use thirst as their cue to get a drink, but thirst does not actually even occur until 1-2% of body water is lost. As you see above, even this small loss can cause stress on the body and limit physical performance. This is why thirst is a terribly weak gauge for the amount of water you should drink.

How much water do we need?

There are 2 main ways to determine fluid intake needs. You can either calculate by metabolic rate (for every 100 kcal of metabolic rate, 80-110 mL of water should be ingested) or by body weight (for every kg of bodyweight, 30-40 mL of water should be ingested). I suggest using the body weight method, as it is easier to do off the top of your head.

Myself, for example: 78 kg x 40 mL = 3.12 L

Since I get roughly 1 L of water from my food, this tells me that I need to drink at least 2.12 L of water daily. This is right on par with most literature, which states that the average person should consume 3 L of water daily. Again though, this is an estimate, and it’s always important to listen to your body. Other important factors to consider include: Body size (the bigger you are, the more water you need), exercise (if you exercise intensely, your daily fluid needs could double), outside temperature (if it’s warmer, you can need up to 500 mL more water regardless of activity level), and diet (high-carb diets help you store more fluids whereas high-protein diets stimulate additional fluid losses due to an increase in urea- a bi-product of protein breakdown).

Long story short, most people will be fine if they consume 2 L of water per day, along with a healthy diet (from which you would get an additional 1 L). Extremely active and/or large people will need to increase their water consumption accordingly.

For athletes and gym-goers

– Make sure you being hydrating before starting an activity/exercise. 500 mL in the 30 minutes before exercise should be the goal.

– During an activity, you should be consuming roughly 250 mL every 15 minutes. Ideally, the beverage will contain a low concentration (6-8%) of carbohydrates and/or electrolytes (eg, sodium, potassium, chloride, calcium and magnesium). This works out to roughly 70 g of carbs + electrolytes in 1 L of water.

– Post-exercise you should again consume extra water. Ideally, this will also contain 10-12% carbs and electrolytes. The maximum rate of fluid absorption by the body is 1.5 L, so feel free to drink this amount each hour until you feel you are rehydrated.

– I would also recommend adding some protein (or preferably, BCAAs) to your during- and post-exercise beverages. This will, among other things, enhance muscle protein synthesis and decrease protein breakdown.

Conclusion

I currently drink 3-4 L per day and get another 1 L from the food that I eat. I exercise intensely 3-4 times per week, and have a high protein diet (increased water loss).  Although I would probably be fine consuming  only 2 L on non-exercise days, I find that my body functions optimally with this increased water consumption- and that’s the name of the game- listening to your body.

As I mentioned in my post about Nutrition on-the-go, I recommend that you all go out and invest in a good water bottle. My Nalgene and I are inseparable. I’m looking at mine right now. I am not thirsty.

If you have any additional questions about why you need water, or about how much water you should personally be consuming, don’t hesitate to contact me!

Happy hydrating!

DW