So I’m still considering the question of gluconeogenesis in breaking down lean muscle during a fast and I’m getting two conflicting answers…
Dr Fung says that protein catabolism flattens out after the first day or so (graph by Dr Kevin Hall):
https://idmprogram.com/fasting-and-muscle-mass-fasting-part-14/
His thesis is that it’s all about whether you exercise or not - and my own experience supports that lack of exercise deteriorates lean mass… but where is the amino acid coming from to fuel the muscle gains? I’m hoping it’s loose skin, but that would require anabolism in the muscle and catabolism in the excess skin…
But other sources say that it lasts for 7 days before the body switches over
Alanine = lean mass breakdown (losing muscle)
Lactate = bi-product of glycolysis in the muscle - Cori cycle (recycled from using glycogen by muscles)
Glycerol = backbone of fats when releasing fatty acids (losing fat)
Propionyl CoA = catabolism of amino acids and fatty acids (losing fat and muscle)
I believe that the difference in duration between the two is that Dr Fung is assuming a fat adapted body and the conventional sources are carb adapted.
Otherwise, my 5 day fast is the equivalent of intentional mass loss since I would be in high level gluconeogenesis for the entire duration…That’s my understanding, at least…
what do you guys think?