Does gluconeogensis consume healthy muscle tissue? Does that change over the course of an extended fast?

Question

Gluconeogensis converts proteins to glucose, but which proteins? Just old, worn out proteins? Or does it really eat away at healthy muscle? Does the answer change over the course of a 3-14 day fast? Once ketone levels rise, does gluconeogensis return to prefasting levels?

Answer 1

Although decreased adipose (fat tissue) constitutes the majority of body mass lost under severe dietary restriction, protein is also mobilized for gluconeogenesis from organs and skeletal muscle during dietary restriction. The proportion of weight lost from adipose tissue vs lean tissue depends on the amount of stored adipose tissue available, meaning that a leaner person with less stored adipose tissue will lose a greater proportion from lean tissue during dietary restriction.