Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How long does it take from food intake to nutrient absorption

  1. Jan 23, 2005 #1


    User Avatar
    Gold Member

    On standardized tests, it is often advised that one should eat an energy bar during breaks to get a boost of energy. But does a person really get a boost of energy during the test? Doesn't food take several hours to digest?

    Also - is it the small intestines that absorb all the nutrients, including calories? What is a rough estimate of absorption time? And are sugars absorbed within a matter of minutes?

  2. jcsd
  3. Jan 23, 2005 #2
    well.. it doesn't take much time to digest sucrose (glucose+fructose), so as soon as the liquid mixture hits the small intestines it is absorbed. Pure glucose requires no digestion at all.

    I didn't take physiology (one of the pracs was to measure glucose levels in the blood after drinking a sports drink), but I would say it would only be a few minutes.
  4. Jan 23, 2005 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes, different nutrients take different amounts of time to digest. Sugars are easily absorbed, although will only give you a short-term boost and then the effects wear off. Fats on the other hand are much slower to digest.

    Of course, not all energy bars are equal. Some are high in sugar, others high in protein.

    With a long test, such as a standardized exam, you'd want to get some balanced nutrients into you so you both have the sugar boost to get you started as well as some slower digesting nutrients to keep you going for the long duration. A long-time favorite is a peanut butter sandwich. The peanut butter offers protein plus fats and the bread some carbohydrates. Have an orange with it if you want (the scent of orange is refreshing to me, and it also provides a healthy sugar boost with good vitamins too). No need to waste money on expensive energy bars.
  5. Jan 24, 2005 #4


    User Avatar
    Gold Member

    Thanks for the replies. From what I've seen in textbooks - food stays in the stomach for 3-4 hours (so I didn't think energy bars would help). But perhaps the smaller particles naturally get into the small intestine - so those particles that have already been small and don't need much more breakdown should give a quicker energy boost, right?

    In other words, do some foods leave the stomach earlier than other foods? I've always wondered if I should eat food just before a standardized test, or a couple of hours before.
    Last edited: Jan 24, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook