Insulin and amino acids
As mentioned above, both insulin and amino acids have profound effects on protein
synthesis and breakdown. Insulin appears to primarily act by decreasing protein breakdown
while excess amino acids directly stimulate protein synthesis (33,34). Therefore, it might be
expected that increasing both insulin and amino acid levels would increase net muscle gain.
When carbohydrates are refed after even a few days of a ketogenic diet, the insulin
response is higher than it would be under normal dietary conditions (38). This is probably due to
the slight insulin resistance which occurs during a ketogenic diet, discussed in chapter 7.
Hyperinsulinemia also increases the transport of some amino acids into muscle (39). These
metabolic effects might contribute to muscle growth during the carb-up.
To maximize insulin levels during the carb-up, high glycemic index (GI) carbohydrates are
preferred. Additionally, one study examining carb-loading after depletion found that insulin levels
were higher with 4 large meals, versus smaller smaller hourly meals although the total amount of
carbohydrates given was the same, as was the glycogen compensation (12).
Cellular hydration
A final way that the carb-load could affect anabolism is by drawing water into the muscle
cells. It has been hypothesized that cellular hydration may affect numerous processes including
protein breakdown and synthesis (40). For example, the extreme protein losses which
accompanies illness and injury is commonly accompanied by cellular dehydration, and increasing
hydration helps to prevent protein losses (40).
As glycogen depletion causes a loss of water within the muscle, the increased hydration
seen with glycogen compensation might affect protein synthesis similarly. However, while it
seems that taking a cell from pathologically dehydrated to normal hydration improves protein
synthesis, it has not been shown that increasing cellular hydration above normal levels will
improve protein synthesis above normal. So this mechanism can be considered speculative at
best, and irrelevant at worst.
A final question
Irrespective of the mechanisms by which the carb-load might cause muscle growth, a
question which must be asked is just how much additional true contractile tissue (i.e. the part of
muscle which is not glycogen, water and electrolytes) can be synthesized during a 24-36 hour
period of carbohydrate overfeeding. In all likelihood, the answer is very little.
Section 5: Setting up a CKD
Having discussed the physiological basis of the carb-load in the previous sections, we can
now examine the specifics of developing a CKD. The low-carbohydrate phase of the CKD is