How Much Water should I drink? The basics of hydration...
Dr. Ivo Waerlop and Dr John Asthalter
Water is the elixir of life. Too much (hyper hydration) or not enough (dehydration) can both be detrimental to your performance, but how much is enough?
Our bodies consist of about 60-70% water at any point in time. Most men have a higher percentage because they have a higher percentage of muscle mass (unfortunately, adipose tissue contains little water!). We generally lose between 1.5 and 2.5 liters of fluid a day through breathing, urinating and general metabolism. The body must keep a balance of water both inside (intracellular) and outside (extra cellular) your cells. Because the body is in equilibrium, if you sweat, breathe, or urinate too much, you will lose water from your extra cellular compartment. The body will then take water from inside your cells and shift it to outside. Likewise, your brain (hopefully) will stimulate you to drink more and urinate less, helping you to fill up the extra cellular compartment again. The water will then diffuse back into the cells and equilibrium is established again. A lot of this movement of water has to do with electrolytes (charged particles in your blood and body fluids) and their movement across cell membranes. The electrolytes that are most important for us are Sodium (Na+) and Potassium (K+).
When you lose too much water, your blood becomes more viscous (remember, you are losing water, not cells. Less water plus same number of cells equals more viscous liquid). This makes your heart have to work harder to push the blood around. This takes more energy and resultantly your heart rate increases, causing a phenomenon called cardiac drift. An example is when you are exercising for a while at the same intensity and your heart rate increases over time. A loss of 2-3% of your body’s water will decrease your performance by 3-7%! The amount you lose will depend on your exercise intensity and duration as well as temperature. A 20 degree increase in temperature can increase your heart rate as much as 10 beats per minute!!
So, it seems if we drink a lot of water, all will be well. Well, yes... and no. Your body can only absorb about 24-28 ounces of water per hour, any more and it just makes you pee more. You can sweat up to 3 liters (that’s more than 96 ounces!) per hour. Hmm. looks like we will probably be in a deficit. How much we absorb depends on whether we can get the water out of our stomach and into our intestines where it can be absorbed. As you can imagine, there are some things which speed gastric emptying and some which slow it down.
Protein and fat are the 2 main things which slow the trip through the stomach down. If too much of these are in your drink or already in your stomach the water will end up sloshing around and probably leave you not feeling too good. Guess that means lots of protein before or during an endurance workout is probably a bad idea, especially if you are trying to stay hydrated! Small amounts of protein, when combined with carbohydrate can be beneficial, but that’s another subject for another day. So much for all that marketing hype!
Small amounts of carbohydrate (up to 60 grams per hour) can enhance water absorption from the intestines and speed emptying of the stomach. The body can’t process any more than this, and it will actually start to slow stuff down if you do too much.
Sodium (50-70 mg, about a pinch) also helps with water absorption. It has the added bonus of stimulating your hypothalamus to tell you to drink more. If you wait until you are thirsty, it will be too late. You need to drink before you are thirsty!
So, what’s a person to do? Here are some tips:
- Drink small amounts often, especially in hot weather. 6 ounces every 15 minutes is a good pace
- Consider adding some sugar to your water sucrose (table sugar) or maltodextrin are a good start. Remember, no more than 60 grams per hour
- If you don’t like sweet drinks while working out, consider using a gel or goo
- A little salt is a good thing. It improves the taste of the water, helps with its absorption, and stimulates the thirst mechanism.
- Research your workout drink. Ask questions. Many claims are marketing hype and not based on science or physiology.
- Consult with your chiropractor, physical therapist, doctor or trainer with questions