In a post about triglycerides, VLDL and carbs, Ned Kock recently commented:
The reality is that very little of the glucose/fructose from carbs gets past the liver in a health person. Muscle glycogen synthase activity is elevated days after an acute glycolitic event (e.g., an intense weight training session).
The liver is a smaller glycogen tank (about 100 g) that fills up quickly, and that is used to replenish the bigger muscle glycogen tank (about 500 g). That happens over time though, and always after the needs of the brain are met.
I need to brush up more on my physiology, but thought I'd do a quick sanity check here. Does this sound right to you? It surprised me. I thought muscle glycogen would be quickly replenished via serum glucose.
The whole glycogen deal is vastly misunderstood by just about everyone in the paleo community from what I read. They are still stuck on the assumption that fructose has to be processed by the liver before it can be used or that once the liver is full fructose will be turned to fat. Its been shown in overfeeding studies that very little of the carbs become fat unless you overfeed massive amounts for days without physical activity. Its also been shown that sucrose behaves nearly identical to pure glucose(starch) in regards to glycogen muscle storage, it even seems to have some benefits over starch with lower insulin levels and faster uptake according to one study.
I doubt what ted said is true based on my personal observations but I don't really see anything in scholar on the subject. Lots of info on glycogen storage after exercise though.
"The pattern of muscle glycogen resynthesis following exercise-induced depletion is biphasic. Following the cessation of exercise and with adequate carbohydrate consumption, muscle glycogen is rapidly resynthesised to near pre-exercise levels within 24 hours. Muscle glycogen then increases very gradually to above-normal levels over the next few days. " http://ukpmc.ac.uk/abstract/MED/2011684
"When 0.35 (low glucose: N = 5), 0.70 (medium glucose: N = 5), or 1.40 (high glucose: N = 5) g.kg-1 body weight of glucose were given orally at 0, 2, and 4 h after exercise, the rates of glycogen synthesis were (mean +/- SE) 2.1 +/- 0.5, 5.8 +/- 1.0, and 5.7 +/- 0.9 mmol.kg-1.h-1, respectively. When 0.70 g.kg-1 body weight of sucrose (medium sucrose: N = 5), or fructose (medium fructose: N = 7) was ingested accordingly, the rates were 6.2 +/- 0.5 and 3.2 +/- 0.7 mmol.kg-1.h-1" http://ukpmc.ac.uk/abstract/MED/3316904
As cliff stated, muscle glycogen stores are replenished at speeds in proportion to the amount of glucose consumed.
There seems to be a lot of misinformation here about CHO intake and fat accumulation. In summary, carbs are converted to fat via a process called de novo lipogenesis. However, de novo lipogenesis occurs in negligible amounts until your entire CHO intake exceeds your total energy expenditure. The body will always prefer CHO to fat/protein for fuel, if available. Here was one study on it: http://www.ncbi.nlm.nih.gov/pubmed/10365981
Unless you're eating something like 700+g CHO a day and are actually exceeding your daily energy expenditure, you get fat not because CHO is converted to fat but rather because lipolysis is downregulated. You aren't burning the fat you eat since you're burning CHO, and it gets stored. VLCDs work for weight loss for a multitude of reasons, but the return to a primarily lipolytic state (vs. lipogenic with high carb + fat intake) is an integral factor.
To answer your actual question, you can check out studies but 24 - 48 hours is sufficient to fully replenish glycogen stores. Ned's statement doesn't jive with what most studies have shown on glycogen replenishment in athletes.
I see what you're questioning, the statement that very little glucose/fructose from carbs gets past the liver.
I'm gonna throw a wrench in this that I'm currently trying to figure out... It appears that liver glycogen isn't re-filled directly from dietary carbs the way many people seem to assume.
I need to read this paper fully, but it shows that liver glycogen is refilled (to a considerable degree at least) via gluconeogenesis.
To be honest I'm not yet sure how this relates to muscle glycogen other than it may be managed slightly differently that just eating starch and letting your muscles absorb it. Maybe not though.
Depends how much glucose you take in. As we know if you take a big hit it''s not going to stay glucose for long. And what I've seen suggests that there's questionable gain to trying to overload things post workout, and only then so as to be able to overtrain. If you have a healthy intense training frequency, then you should be able to refill your glycogen over several days from your normal paleo carb intake/gluconeogenesis if that's your thing.
There's still some CW around I think that suggests that the glucose helps with the uptake of protein, which I hear is not necessary.
So the question is, when you go for your PWO sugar rush, does the insulin preferentially shuttle glucose to the muscles? Fructose has to go to the liver first, so that's a non-issue, but glucose can be used and stored directly. However it seems to me reasonable to think that at best, muscle and liver glycogen are replenished at the same rate, and once the liver is full it's going to start converting to fat while your muscles are only 1/5th full. I think you'd be able to push on and get a lot into the muscles, but only at a cost which may seem counter-productive depending on your goals. Health or performance.