This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
It has been shown by investigators that the skeletal muscles may lose 40% of their weight, whereas, the heart muscle loses only 3% by the time death from starvation is reached. The decrease in the size of the muscles extends also to their cells, which similarly decrease in size. Probably there is not an actual lessening of the number of muscle cells in a fast of ordinary duration, but only a consumption of fat, glycogen, and lastly some of the muscle protein and a lessening of the size of the cells. This loss of fat and muscle might occur at any time without damage to health.
In general the skeletal muscles are affected earlier and more intensely than the smooth muscles. There seems to be no actual decrease in the number of muscle fibers, but only a diminution in the size of their cells. The cells are merely reduced in size but remain perfectly sound.
In frogs and salmon, fat is stored in the muscles during the eating period, and consumed during the fasting and hibernating period. The decrease in size is due to a loss of fat, not of muscle. Much the same phenomena are often observed in fasting patients.