The Science of Fasting

Beast said
I'm not sure how you can say that fuel/food cannot build muscle. Amino acids, the building blocks of protein, are the basis for lean tissue creation within the body. Amino acids cannot be created by the body and must come from a food source. Without that, you're not laying the foundation for any muscle growth via exercise.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2430042/

That's why I was asking if anyone doing extended fasting was concerned about the loss of lean tissue via fasting. Most research says anything beyond 16 - 18 hours becomes catabolic in nature. Beyond a certain point, the losses may minimize, but it's still loss of important tissue.

I've read stuff by pro-fasting sites that claim that you can go up to 3 days or so without losing muscle, as long as you keep working the muscle. I think they linked to a study, but I'm not sure.

I suspect it's a YMMV kind a thing.

The basic idea is your body isn't stupid... if you are using your muscles (and by that they mean actually pushing them hard, not light work), then your body will know that they are needed and burn fat, since it assumes you will need those muscle to procure more food.

I don't have links to those studies, so....