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View Full Version : Fructose and carb depletition (UD2.0)



TheGimp
05-20-2004, 04:24 PM
So everyone knows that fructose "preferentially refills liver glycogen". And glycogen depletition is all about depleting muscle glycogen. Does this mean you can get away with eating more carbs if they're mainly fructose? What does preferentially refills liver glycogen actually mean? If liver glycogen is full then muscle glycogen gets refilled?

Shao-LiN
05-20-2004, 11:11 PM
Yes, once liver glycogen stores are full, the rest will "spill over" into muscle/fat cells.

TheGimp
05-21-2004, 12:26 AM
I'm guessing this is pretty hard to answer, but how many grams are we talking before this spillover occurs? If the fructose consumption is spread out over the day can the spillover be prevented?

Shao-LiN
05-21-2004, 08:04 AM
You'd have to ask Lyle...I have no clue on the grams.

aka23
05-21-2004, 10:24 AM
I'm guessing this is pretty hard to answer, but how many grams are we talking before this spillover occurs? If the fructose consumption is spread out over the day can the spillover be prevented?

It depends on many factors. I think it would be safe to say at least 50g. 50g is a conservative limit that is usually assoicated with rats (poor model becuase they use different fat conversion pathways from humans) or men with health problems, mainly known elevated triglycerides (tendency to convert to triglycerides). Some studies suggest much higher limits:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8116555&dopt=Abstract
"Ordinary intakes of sucrose or fructose do not have any special elevating effect on plasma triglycerides in most normal and diabetic people, provided energy balance is not changed. Although biochemical theory predicts that fructose is more lipogenic than glucose, nearly all the animal reports of elevated plasma lipids with sucrose- or fructose-rich diets were obtained with diets unnaturally high in these sugars, and in rats and not other species. In humans, increased (fasting) triglycerides are observed with very high intakes, > 35% of energy from sucrose or > 20% of energy from fructose, and even then triglyceride elevation is unlikely unless the subjects are male and dietary fat is saturated."

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=756709&dopt=Abstract
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11145118&dopt=Abstract

If you are cosuming excess calories, there may be a spillover to fat. However, excess calories are probably going to end up as fat, regardless of their source. Liver glycogen can supply energy to the entire body, unlike muscle glycogen which is limited to muscles. When stores are high the body burns liver glycogen at an increased rate to prevent such a spillover. In my opinion, you do not need to worry about such a spillover unless you have a high-sugar diet, special health problems, or a special diet (such as a refeed).

aka23
05-21-2004, 10:45 AM
So everyone knows that fructose "preferentially refills liver glycogen". And glycogen depletition is all about depleting muscle glycogen. Does this mean you can get away with eating more carbs if they're mainly fructose? What does preferentially refills liver glycogen actually mean? If liver glycogen is full then muscle glycogen gets refilled?

You would want to deplete both liver and muscle glycogen to maximize fat oxidization. You cannot get away with eating more carbs if they are fructose or galactose. If anything, it would be the other way around. You might want to limit (but not eliminate) your fructose/galactose/sucrose/lactose consumption.