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How long for ingested subtances to be used?

  1. Jan 20, 2004 #1
    Just curious how long it takes for carbohydrates to be broken down to glucose etc. and proteins to be used for all the types of synthesis they're used for once they're ingested?

    I was thinking about those sports drinks which have alot of sugar. In the past it made sense that drinking something sweet during physical activity would supply sugar for respiration, but doesn't it take something like 15 hours for digested food to reach the large intestine where absorbtion of nutrients takes place? Are there other places in the digestive system where things can be absorbed, or do liquids travel through the digestive system faster?
  2. jcsd
  3. Jan 23, 2004 #2
    It REALLY depends. A complex carbohydrate source high in fiber, like whole-grain bread takes much longer to digest than sugar water. A steak takes much longer to digest than a protein drink made up of short peptides. You get the idea.

    Fiber, fat, and insufficient amounts of liquid generally delay digestion. Also physical activity may delay digestion (blood is moved out of the colon to supply the skeletual muscles, see fight-or-flight reaction).

    As for recommendations, it depends on the kind of exercise. For your average 30-60 minute strength or endurance session, it's a good idea to be fed & rested (but not have a full stomach) before you begin; i.e. eat 2 hours prior to exercise. Immediately after exercise, suppl ythe body with easily digestable nutrients such as high-GI carbohydrates (and a protein shake after weight lifting).

    -The body needs nutrients during exercise. Dont starve yourself during the day before exercise: Feed yourself until about 2 hours before you start.
    -The need for nutrients is most critical AFTER exercise, as glycogen stores are depleted & very receptive to carbohydrates for a "refill", you need some carbs to keep blood sugar constant w/o breaking down too much muscle tissue, and muscular growth through super-compensation occurs only if nutrients are readily vailable after exercise. So your pre-exercise meal will leave your stomach and be absorbed into the bloodstream just in time.
    -a high absorbtion of nutrients shopuld be ebsured for several hours after the workout. that's what the post-exercise shake can accomplish. Also, it triggers a desirable endocrine response: After a strongly catabolic phase during workout, in which nutrient stores like glycogen stores and the amino acid pool were depleted, you want your body to switch into anabolic mode to repair the tissue damage & adapt to the stress you exposed it to so that it can handle it still better the next time. When you taste sweet things (like a drink rich in simple sugars), catabolic hormone levels are reduced and anabolic hormones like insulin and IGF-1 are released.

    Also, the night following your workout, you'll want to get a good 8 hours of sleep because much of the adaption is facilitated by somatotropin (human growth hormone, HGH) -- most of which is released when we are sleeping.


    This is just a rough guide for people training for general fitness, maybe with an emphasis on strength training. Professional athletes often have a nutrionist who calculates what they eat and when they eat it just for that one particular person to best suit their needs! The recreational athlete can always educate himself and learn about nutrition as much as he can, but fot the fine adjustments it's back to (educated) trial and error.

    Hope this answers your question ;)
  4. Jan 23, 2004 #3


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    The important ingredients in sports drinks are not the sugars, they are electrolytes. The sugar is really just there to make it palatable. They are pretty much bottles of sweat, with the urea removed, and sugar added. The electrolytes, being very simple ions, can probably get into your bloodstream in minutes I'd bet.

    I liked it better before they added all the extra flavor. Sure, Gatorade used to taste like sweat, but that made it a great diagnostic tool. When the Gatorade started to taste good, you knew you were dangerously dehydrated.

  5. Jan 23, 2004 #4
    Njorl -
    I concur. Products like Gatorade resupply the body with electrolytes, which the body loses by sweating. Since we're talking about liquids, they can pass through the stomach within 10-20 minutes and are absorbed immidiately thereafter.
    My points about macronutrients remain valid though.
  6. Jan 23, 2004 #5

    You are completing missing on the restoration of glycogen levels, which are a must post workout. The replacing of electrolites is important for muscle activity and the isotonic solution of Gatorade is perfect for replaceing the electrolites without flushing excess liquids through urination. But for recovery, glycogen is extremely important.


    Are you a nutritionist???

    Have you ever heard of protein overloading. Bodybuilders will actually use 600 to 700 grams of protein per day along with zero (as close as possible) carbs. Along with this they will shoot insulin post workout (10 - 20 ius) and instead of the usual carb shake to go along with this they take in their protein. They can do this without going into hypoglycemia, which must be a radical adjustment for the body. If consumption of carbs is over 5 to 10 grams that day, they will go into hypo after the shot of insulin and will have to consume sugars immediately in order to remain conscious

    I have seen people put on 10 to 15 lbs of pure muscle while loosing 3 to 4 percent of their body fat.

    No real point to this post, but I thought it was interesting and sicne you seem to know about nutrietion and training, I thought you might find it interesting (or maybe insane).

  7. Jan 23, 2004 #6


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    The only time I used Gatorade was when I was doing "SCA" fighting. It is re-enactment of medieval warfare. The actual workout is mild, but the heat in the armor is sometimes brutal. So, you burn few calories, but sweat buckets.

  8. Jan 23, 2004 #7
    So are you saying the sugar in gatorade and other sweet sports drinks doesn't supply you with glucose for respiration during the exercise?
  9. Jan 23, 2004 #8
    yes it will, after 10 minutes. If you are doing a long term activity you must keep your body hydrated, electrolites up, and glycogen levels up by supplementing before the levels have dropped. It is easier to maintain then it is to play catch up.

  10. Jan 23, 2004 #9
    Where does all this absorbtion happen? Does the liquid just get to the large intestine in 10 minutes or are there places along the way which specialize in absorbtion of certian things?
  11. Jan 25, 2004 #10
    No absorbtion before it reaches the stomach. But liquid does not have to be digested so it can pass the stomach relatively quickly.

  12. Jan 25, 2004 #11
    No Im not a nutrionist But I think it's pretty cool I can use my bio studies toward my weight lifting routine.

    I've heard abut proetin overloading, but never saw anyone actually do it.

    Why can't they eat any carbs? Would carb ingestion inhibit gluconeogenesis, or the passage of keto bodies into the brain..?

    I'm not saying people shouldnt do this kind of stuff, but I for one wouldnt. They'd better make sure to drink tons of water around the clock - they'll be getting a large share of their energy needs from gliconeogenesis, and that's HUGE stress on the liver. W/o enough water the urea will crystalize and then, you know... I guess you can do that if you're not doing it all the time, are under supervision, and have the time and ressources to ensure perfect planning of your nutrition throughout the day, i.e. dont have to go to work etc.
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