Is it necessary to eat some fructose?
Is there such thing as fructose deficiency?
If you never eat fruit and only eat starch for your carb consumption in order to avoid liver glycogen repletion is there any long term concerns to eliminating fructose from the diet that anyone could think of?
It just seems to me that fruit and therefore fructose consumption is not only ubiquitous in nature (despite Eskimo territory) but also we have a taste for sugar.
The latter however may be due to childhood conditioning around sweets: think easter, christmas, birthdays, valentines day, thanksgiving, halloween, as well as convenience stores and refined carbohydrates everywhere as well as juice packs and elementary school lunches.
Sperm are obligate fructose consumers, so there's that. But your body can manufacture fructose as necessary, so it's non-essential in terms of diet.
I have searched in vain for good links to provide regarding how we make fructose. Having failed, I'll simply do my best to elaborate.
Human de novo fructose synthesis is a two-step process involving sorbitol as an intermediary between glucose and fructose, as follows:
aldose reductase sorbitol dehydrogenase
glucose ------------------------> sorbitol ------------------------------------> fructose
The first step of this reaction is the primary pathogenic process of diabetes, where glucose is irreversibly converted to sorbitol in tissues containing aldose reductase: lens, retina, Schwann cells, liver, kidney, placenta, RBCs, ovaries, and seminal vesicles.
The reason this is problematic is that very few tissues contain the sorbitol dehydrogenase enzyme necessary to convert sorbitol to fructose. These tissues are liver, ovaries, and seminal vesicles: the only tissues listed above that have no diabetic pathology. In liver, this process provides a way for sorbitol to enter the glycolytic or gluconeogenic pathways. In the seminal vesicles, it provides fuel for sperm motility. The function is not clear in ovaries.
The reason this first step is problematic in diabetes is the inability of sorbitol to effectively leave the cytoplasm of cells: this results in an altered osmotic gradient, swelling, and loss of function (cataracts, peripheral neuropathy, vascular damage, et al.).
Liver glycogen will be replenished by starch - just not as quickly as by sugar (glucose/fructose). Unless the liver or the gut needs fructose for some reason, then the answer is that fructose is probably not necessary. Sure, we have a taste for it. There is an evolutionary advantage to eating fruit when it is available. Food is life - no food is death.
No it's not, no carbohydrate is, as protein can be used to replace the missing glucose. On the other hand, fructose has a lot of advantages. Nothing powers up the liver as quickly as fructose.
For me, eliminating fructose was a mistake. The success of Ambimorph and other zero-carbers make me realize my experience should not be generalized.
Following on from the answer by interrobung.
It would seem that fructose is indeed necessary, at least for males wishing to reproduce.
Tho it would also seem that we do not actually need to source fructose from our diet;
According to the article ref below, the (male) body can produce fructose from blood glucose.
Having said that, it looks like that particular gem of information comes from a study on rats.
I found a few studies/articles that talked about the source of fructose in semen originating from the seminal vesicles and to a lesser extent from the ampullary glands. But only the one below mentioned how the fructose was produced.
"The main site of fructose formation is the seminal vesicle yet; an additional small amount comes from the ampullary glands. Fructose synthesis is hormone dependent process, it disappeared almost completely within 2 weeks after castration, while was prevented or restored by implantation of testoterone, since seminal vesicle are testosterone dependent (7).
The seminal fructose concentration is primarily an indicater of the size, storage and secretary capacity of the seminal vesicles and of human androgenic activity (8).
Biosynthesis of seminal sugar involves the conversion of blood glucose into seminal fructose (9)"
Another ref source: "The biochemistry of semen"
Looking at some studies on pregnant women (did i need to specify women?), it looks like we may all have the capacity to produce fructose endogenously.
here are a few refs:
Fructose in fetal cord blood and its relationship with maternal and 48-hour-newborn blood concentrations
"Fructose production by the sorbitol pathway, present in the fetus and newborn, is an alternative pathway in glucose metabolism probably used to maintain redox balance in the fetus.
We suggest that endogenous fructose, similar to dietary ingested fructose, under physiological conditions produces the backbone for triacylglycerol and lipid synthesis in the fetus and newborn. Therefore the route for metabolizing fructose is already present in the early steps of human development."
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