A low carb diet spares protein while it sheds fat. I posted a link to one paper on that. Here:
Very Low Carbohydrate Diet and Preservation of Muscle Mass
http://nmsociety.org/index.p....emid=44
bottom of page
About liver glycogen and catabolism.
Liver glycogen:
Mobilization of glucose from the liver during exercise and replenishment afterward.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Gluconeogenesis, link from wikipedia:
http://en.wikipedia.org/wiki/Gluconeogenesis
Quote:
"Gluconeogenesis is the generation of glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and glucogenic amino acids."
Glucose can be made using more than just protein. For instance glycerol, the binding agent in triglycerides (dietary fat or stored fat), can be used, sparing protein. Also, by definition, a low carb diet includes more protein and more fats. So, if protein is used, more is coming in from food. Same with fats. If glycerol is used, more is coming from food. We can also look at it the other way. If more protein and fats are coming in, then that is what will be used instead.
When I think of catabolism, I think of protein breakdown without an equivalent protein synthesis to compensate. I don't include protein intake but we should consider it in the overall balance. I'd like it if you could elaborate on what you mean by catabolism. Also, what's your specific concern so I can pinpoint what I'm looking for. I'm thinking you mean especially cortisol as the catabolic agent to avoid. Is that correct?
Role of cortisol in the metabolic response to stress hormone infusion in the conscious dog.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Quote from the abstract:
"The role of cortisol in directing the metabolic response to a combined infusion of glucagon, epinephrine, norepinephrine, and cortisol (stress hormones) was investigated."
Note that cortisol is not the only hormone that can stimulate gluconeogenesis. Glucagon is made by the pancreas (it's like the anti-insulin) and is particularly effective at sparing protein because it also stimulates fat mobilization so there's more glycerol available to do the job.
I should note that cortisol is more elevated overall and over the long term in a high carb diet than in a low carb diet because of the wildly fluctuating blood glucose levels especially during and after a high carb meal. When blood glucose level drops, cortisol is released to bring it back up. If we eat high carb all the time, blood glucose level constantly drops and cortisol is constantly being released to bring it back up. Up and down day in day out.
Acute glucocorticoid effects on glycogen utilization, O2 uptake, and endurance.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Role of cortisol on the glycogenolytic effect of glucagon and on the glycogenic response to insulin in fetal hepatocyte culture.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Divergent effects of actinomycin d on cortisol and on glucose stimulation of glycogenesis in mouse liver.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
I didn't read much of the papers I linked. I just figured from the abstracts they were somehow relevant here. Some are available in full text for free. See a link upper right.
Low carb diet and cortisol papers:
Dietary macronutrient content alters cortisol metabolism independently of body weight changes in obese men.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Duration 4 weeks.
The metabolic response to a high-protein, low-carbohydrate diet in men with type 2 diabetes mellitus.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Duration 5 weeks.
Body composition and hormonal responses to a carbohydrate-restricted diet.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Duration 6 weeks.
The effects of carbohydrate variation in isocaloric diets on glycogenolysis and gluconeogenesis in healthy men.
http://www.ncbi.nlm.nih.gov/pubmed....VDocSum
Duration 11 days.
Note the duration of the studies. From 11 days to 6 weeks. Earlier, I pointed out that a low carb diet takes some getting used to before things begin to go back to normal. The period where things don't look normal is about 2-4 weeks. Only after this period can we draw solid conclusion about most everything that goes on hormone wise.
But, if you only want to know what happens when you cycle carbs every week, then those studies should give you some good answers. I suspect that the carb cycling diets are based on the fact that the only studies available on that subject are of short duration and so can only tell us what happens during that "abnormal" period.
A note on dehydration. Water is lost during the first week or so when switching to a low carb diet. This is normal. Glycogen requires about 2-3 times its weight in water. Once the gycogen is gone, the water is not needed anymore so it's excreted. It's not a dehydration in the classical sense. It's merely a discarding of unneeded water. Dehydration is the loss of needed water.