Skeletal Muscle Lipids

The effect of fasting on skeletal muscle lipids has been studied.The amount of phospholipid per g of muscle remained constant throughout prolonged fasting, although when death is imminent it appears that a small fall in phospholipid concentrations may occur.The distribution of lipid phosphorus among the various phospholipid subclasses was not found to be influenced by fasting.Triglyceride tended to increase in muscle during the early stages of fasting but was ultimately depleted when the period of fasting was quite prolonged.Muscle free fatty acids (FFA) were markedly increased during fasting, and evidence is presented that the changes in muscle FFA were not merely a reflection of the changes occurring in plasma FFA.The conclusion is drawn that the phospholipids of muscle are structural-functional elements that are not depleted during fasting for purposes of energy metabolism.It is also concluded that muscle triglyceride does not serve as an energy reservoir to be drawn upon rapidly during caloric deficiency, although if caloric restriction is su5ciently prolonged the triglycerides are then drawn upon to the point of nearly total depletion.