I'm hoping someone can point me in the right direction if this topic has been covered here or on Dr Fung's website.

Protein turnover is going on constantly and I was taught (admittedly a long time ago!), that lean tissue would be broken down to release essential amino acids during fasting so that protein synthesis of essential proteins could continue. This would likely result in loss of lean muscle mass. Yet, Dr Fung categorically states that this does not happen.

I have been unable to find a convincing explanation for why/how muscle mass would be preserved while fasting, even in the presence of growth hormone.