Can your digestive system convert fructose into glucose?
I’ve heard Dr Andrew Weil say that people can survive on intervenous feeding of glucose alone for quite some time but very little time on fructose. I believe he was implying that fructose is an inferior sugar.
But isn’t the body’s digestive system able to convert fructose into glucose in any event? Any savy nutritionists or doctors out there who can give me insight?
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Filed under: digestive system
In biochemistry is was said that fructose is converted into glucose in the liver. Now keep in mind, when someone says digestive system they are usually talking about the stomach and intestines. Lets go over a few things:
1. Fructose is just an isomer of glucose. Isomers are easily converted between each other, if you have the right enzymes.
2. Fructose is not directly used in creating energy for the body, it must first be turned into "glucose like" molecules
/—-> GA —–\GAK
FK F1P ald / \
fru ——-> fru-1-P ———- ——-> 2 GA-3-P - - - - >
\ /
\—> DHAP —-/izo
3. No energy is used in this system (thats not to say energy isn’t used in the creation of the enzymes). Once you have 2 Glyceraldehyde 3-Phosphate molecules, you are ready to begin the Krebs cycle, and its from this you get most of your ATP (the bodies energy)
Anyway, in the human body Its almost safe to say their are no closed systems. As long as molecules can be converted into something of use, you can live.
Fructose is not an inferior sugar as it does feed sperm. As well as sperm, it is easily converted into glucose almost instantly when needed.
Please note inter-venous feeding does not go through the digestive system, therefore the complex sugar fructose is not converted to the simple sugar glucose.
I am not a doctor.
In glycolysis performed on the liver, the first step is the phosphorylation which is the controlling step in setting the speed of the reaction.
The glucose 6 phosphate is isomerized to fructose 6 phosphate.(then phosphorylated again)
The enzyme the phosphorylates fructose directly to fructose 6 phosphate is NOT controlled.
What this suggests is that fructose intake can consume the available ATP within the mitochondria.
So, technically, fructose 6 phosphate can be converted to glucose 6 phosphate but the reaction is primarily in the other direction due to the energy gradient.
See:
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch15_glycolysis.jpg
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch15_reg-glycolysis.jpg
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch15_E-landscape_glycolysis.jpg