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How quickly is water absorbed after you drink it?

October 19th, 2011

I’ve always been curious about this. Sometimes, after drinking a big glass of water, it seems like I pee it all out literally just a few minutes later. Is this just in my head, or is ingested fluid really processed that quickly? A new study by researchers at the University of Montreal, published online in the European Journal of Applied Physiology, takes a very detailed look at the kinetics of water absorption and offers some answers.

The study gave 36 volunteers 300 mL of ordinary bottled water, “labelled” with deuterium (an isotope of hydrogen than contains a proton and a neutron instead of just a proton) to allow the researchers to track how much of that specific gulp of water was found at different places in the body. They found that the water started showing up in the bloodstream within five minutes; half of the water was absorbed in 11-13 minutes; and it was completely absorbed in 75-120 minutes.

Here’s what the data looks like:

On the left, it shows how quickly the water was absorbed in the first hour, measured in the blood. On the right, it shows the gradual decay of deuterium levels over the subsequent 10 days, measured from urine samples. This, of course, shows that when I pee after drinking a glass of water, I’m not peeing out the same glass of water! Within ~10 minutes, fluid levels in my blood will have risen sufficiently to trigger processes that tell me to pee — but, according to this data, it takes about 50 days for complete turnover of all the water in your body.

The other wrinkle in this data is that the subjects showed two distinct absorption patterns (shown on the bottom and top), with about half in each group. In the top group, the water is very rapidly absorbed into the blood (possibly because these people get water out of the stomach and into the small intestine very quickly) before running into a slight bottleneck as the water is then distributed throughout the body to all the extremities. The second group, on the other hand, doesn’t hit this bottleneck: the flow of water out of the stomach and into the small intestine is slow enough that extra water doesn’t have a chance to build up in the blood before being distributed throughout the body.

So what does this all mean? I don’t have any particular practical applications in mind — I just thought it was kind of cool.

  1. Scott
    October 19th, 2011 at 21:08 | #1

    Fatal flaw in the study.

    D2O interacts completely differently with Type II and P-Type ATPases (water exchangers in nephritic microvilli and glomerular tubes), as well as any other process that is based on hydrogen bonds. The upshot is that anything with D20 is going to happen much slower than it would with H20.

    For that very reason, D20 is used in perturbance studies of reaction kinetics.

  2. AG
    October 19th, 2011 at 23:01 | #2

    I have noticed I can smell stinky pee (aspartic acid?) within minutes after eating asparagus. I’m going to have to try a delicious experiment.

  3. Rob Geurtsen
    October 20th, 2011 at 00:27 | #3

    @Scott

    Scott, what’s your source or any reliable reference regarding D20/H20.

  4. RH
    October 20th, 2011 at 08:13 | #4

    To me it signifies that a drink can hit the spot.

    The curves look like a Levy-distributions with an exceptionally heavy tail. As I understand, that is also the distribution of a particle passing a certain place at a certain time under Brownian movement.

    If it is a Levy distribution, water exits with a factor 1/x^3/2. After all the posts on allometric scaling, that suggest a surface, shrinking when the volume contained within it drops. That is exactly what it feels like :)

  5. Graydon Snider
    October 20th, 2011 at 17:39 | #5

    @Scott
    I dunno. Seems these ‘fatal flaws’ were addressed quite some time ago (am I wrong? It’s not my field):
    THE MEASUREMENT OF TOTAL BODY WATER IN THE HUMAN SUBJECT BY DEUTERIUM OXIDE DILUTION WITH A CONSIDERATION OF THE DYNAMICS OF DEUTERIUM DISTRIBUTION
    J Clin Invest. 1950; 29(10):1296–1310
    http://www.jci.org/articles/view/102366/scanned-page/1296

  6. Scott
    October 20th, 2011 at 20:50 | #6

    @Graydon

    I stand by my assertion.

    There’s simply no way to come up with a universal fudge factor that covers the millions of interactions on the molecular level in an individual based on a statistically insignifcant* sample size.

    * 4 samples? Are you kidding me? How did that get published? (See p. 1299 of the paper you cited.) They might as well just thrown four darts at a wall for their numbers.

  7. alex
    October 20th, 2011 at 21:18 | #7

    @Scott: On the other hand, can you offer any evidence to suggest that D2O and H2O are processed at significantly different rates? This isn’t something I know anything about, so I’m entirely open to being convinced. But at this point, four samples is more than zero!

  8. Milt Mac
    October 20th, 2011 at 22:04 | #8

    In 2000 Ironman world championship on the bike with a tailwind for over an hour every time I took Electrolyte in [every 30 minutes] in 7 minutes my thigh muscles would “tingle” I figured it was blood moving away from them to process the sugars

  1. October 19th, 2011 at 19:49 | #1