I realise this is not your view jksinrod, but I thought I would add a little bit about glycogen just so you know the summary of the report you provided is nonsense from the very beginning!
- I'm sure he won't mind me posting this here, but these are the words of Gabriel Guzman posted on the Protein Power forum - (Gabe is a biochemist who actually knows what he is talking about here!)
"Q: Are muscle glycogen levels kept relatively constant? Meaning, is there a 'set' level of glycogen that the muscle and liver likes to keep in stock, so to speak? Or is it purely a function of how much carbohydrate you eat?
A:Yes, there is a level of glycogen in the muscle that is always kept. Although we normally talk about "glycogen depletion", in the case of the muscles, which is where most of the glycogen is stored, their content fluctuates less markedly than that of the liver.
The human body can store up to ~450 g of glycogen (THATS ONE POUND NOT TEN!), a third of that in the liver and the rest in the muscles. Is important to understand that the glycogen in the liver serves, above all, in the maintenance of the blood glucose level. Muscle glycogen, on the other hand, serves as energy reserve, and it is not involved in maintaining blood glucose levels. The reason for this is simple: muscle lacks an important enzyme that converts an intermediate into glucose. The intermediate itself cannot leave the muscles a go into the bloodstream.
Muscle glycogen is never completely degraded. So, let's say that the muscle can store up to 300 g of glycogen, at least two thirds of that remain fairly constant. Extreme situations such as prolonged fast (true starvation) results in the depletion of protein, rather than glycogen (remember that glucose produced from glycogen canot leave the muscle).
Q: Is there a blood test or some other way to measure glycogen state?
A: I don't think you can measure glycogen state in a blood test. Glycogen is never free in the blood stream. However, it is possible to measure the rate of glycogenesis and
glycogenolysis (the making and the breakdown of glycogen, respectively). There is also a recent breath test that measures liver glycogen oxidation. I think these tests are normally useful in the assessment of diseases related to glycogen storage or utilization.
Q: Does carbohydrate loading actually increase the amount of glycogen available? Or is there a maximum amount of glycogen 'space' as it were?
A: That has always been debated. Since the liver content of glycogen is the one that fluctuates the most, that is the one that is synthesized first in the well-fed state. Now, this assumes that there is enough carbohydrate in the diet for glycogen synthesis. Muscle glycogen reserves, since they don't fluctuate that much, are not likely to be altered by carbohydrate loading. This, of course, needs to be put in the right context, and here one needs to distinguish between those who constantly put an energy demand in their muscles and those who are sedentary. Sedentary people rarely deplete their muscle glycogen and since there is always a "base line glycogen", probably not even very active people can completely deplete their muscle reserves of glycogen. So, it is the liver reserves the ones supplied first. After that requirement is met, and since the muscles replenish only a fraction of what they already have, excess carbohydrate doesn' go into glycogen synthesis but to other pathways, such as fat synthesis.
Q: I'm assuming that people who eat LC create glycogen from available amino acids, and tend to replenish their stores this way after severe exercise, perhaps slower?
A: That is only if there is a need for it. Remember that the only purpose of having glycogen is to 1) maintain blood glucose levels and 2) supply energy to the muscles. Those on a carbohydrate-controlled diet still make glycogen with whatever carbohdyrate comes in the diet (note that LC may mean different things). People who don't eat carbohydrates at all (because of geographical locacion where no carbohdyrates are availabe, for example), would supply their muscles with glucose made de novo by gluconeogenesis.
Q:I would think that humans would be engineered to provide a way to create this turbo-charging fuel even if the diet didn't contain large amounts of carbs.
A: Precisely, and gluconeogenesis is one such mechanism. Evolutionary, it is important that the muscles always have some glycogen that they can use for a quick, but powerful, production of energy. That could be the difference between life and dead in a hunter-prey situation. For example, think of an animal that's feeding. It could be us sitting next to a nice fire or a deer grazing. The metabolic status in which feeding stimulates insulin release would at the same time shut down those pathways controlled by glucagon. However, if a predator appears, the animal should be able to flee the site and for that it needs a powerul generation of energy to run, thus it is necessary to have glycogen available for quick glycogenolysis, which in turn produces glucose that is used by the muscles. For liver glycogen to be replenished, it's not necessary to load excess carbohydrate."
The whole thread is here if you are interested;
http://bbs.eatprotein.com/viewtopic...hlight=glycogen
Cheers,
Malcolm
ACSM rebuttal?
, I would have to disagree here. Whilst all athletes "use up" available glycogen first, sprinters are one class of athlete who will probably perform better on higher carbs because the conversion of metabolised fat for energy is not fast enough for the sort of explosive bursts they require. Endurance athletes on the other hand, if they adjust to a low carb diet* have been shown to improve their performance by utilising fat as the predominate energy source. Another benefit of this option is reduced lactic acid production (a byproduct of glucose metabolism.)
Linear Mode
