Originally Posted by Dare Vodusek
At least I think it works that way, but im sure Darryl will post some link saying otherwise
You're forgetting that liver glycogen is used to maintain blood glucose levels both in the fasting state and in the fed state if carbohydrate intake is insufficient to meet demand, as would be the case with a low carbohydrate diet. Once liver glycogen stores are depleted protein is diverted to energy production and so can not be used for repair or growth. And while this conversion of amino acids to glucose (gluconeogenesis) can maintain blood glucose levels at rest or during light exercise, glucose can not be produced in this way at a rate sufficient to fuel intense exercise. Therefore carbohydrate is required to provide an immediate source of energy, replenish both muscle and liver glycogen stores, and spare protein for repair and growth.
As for carbohydrate being stored as fat when glycogen stores are full, yes technically speaking that would happen if stores were full. However, our capacity to store carbohydrate as glycogen is significantly greater than our typical dietary intake, which is why you rarely find evidence of de novo lipogenesis making any real contribution to fat stores outside of overfeeding studies where subjects are fed huge amounts of simple sugars over a number of days.
Biochemistry. 5th edition - Section 30.3: Food Intake and Starvation Induce Metabolic Changes.
Substrate utilization during exercise in active people.
Edward F Coyle. Am J Clin Nutr 1995;61(suppl):968S-79S.
*All links wfs*