Absorption of Water vs. Other Liquids

Our good friend at Pawsitive Life asked “Does water get processed faster by the body than other liquids?”. I strongly suspect this has something to do with her continuing struggle to switch to water from Coke Zero. Please remember that nutrition is an ever-changing and controversial subject. While I’ve taken courses on sports nutrition, it remains an area of active research and there exist opposing viewpoints. That being said, here’s the final, unassailable and absolute right answer.

Trust us, we’re scientists!

“Processed” is a tricky word in this context, because water isn’t really processed at all. Being the solvent of our bodies’ internal environment, one could argue it is pressed into service as soon as it enters the mouth. More to the point, perhaps, is the question, “Does plain water quench my thirst and rehydrate me faster than other liquids?”

First off, thirst originates from a higher than normal concentration of stuff in the blood. This creates an osmotic pressure difference that is sensed by the hypothalamus (= part of brain). Water, whether pure or caramel coloured (and according to some, more delicious), is absorbed mainly in the upper small intestine, the duodenum (pronounced doo″o-de´num, for all our American friends), by following the osmotic gradient across the intestinal lining. So, whatever will quench thirst and rehydrate fastest will be the liquid that gets the water in the intestine absorbed fastest.

One might be led to believe that pure water would be the quickest across due to the highest osmotic difference. However, the literature (not to mention the marketing) suggests that water containing some sugar and sodium and with hypo-isotonic molality is absorbed fastest.

Since molality isn’t listed with the nutritional information, let’s stick to those things we can readily compare, sugar and salt. These nutrients are used or lost during exercise There is a trade-off, however. It seems that sugar delays the fluid from leaving your stomach, and therefore delays absorption. Likewise, if the liquid contains too much sodium net water flow moves into the intestine, not out of it. According to Brouns and Kovaks (Functional Drinks for Athletes, 1997), the ideal for absorption is:

  • Sugars: 60-80 g/L
  • Sodium: max 1.1 g/L

Coke Zero, containing 0 sugar and 1268 g/L of sodium falls outside the envelope (Sorry). Other sodas, juice, and energy drinks don’t work either. Chocolate milk has gained attention recently as an after-exercise drink, and in fact does comply with guidelines if taken with an equivalent amount of water. Milk also delivers quality proteins for muscle recovery within the critical 60 minute after-workout window (too bad you don’t like milk either). Not surprisingly, sports drinks such as Gatorade and Powerade are right in the sweet spot.

Bear in mind, the operative word for all these options is “sweet”. These beverages are made to be taken after endurance exercise lasting around 1 hour. If you were taking all of your daily water requirement of ~2L through Gatorade, you would also be drinking ~12 teaspoons of additional refined sugars.

Like it or not, in day-to-day life regular meals ensure that enough solutes should be present in the gut to allow rapid absorption of plain, good old fashioned water.

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3 Responses to Absorption of Water vs. Other Liquids

  1. Pingback: Tempest in a Teacup | Quick! To The Lab!

  2. pawsitivelife says:

    I knew life was against me!


  3. ElenaSC says:

    Very interesting! Thank you for sharing.


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