What is the primary energy source for the myocardium after fasting?

The primary energy source for the myocardium after fasting is fatty acids. During fasting, the body shifts its metabolic pathways to utilize fatty acids as the main fuel source. This is primarily due to decreased insulin levels and increased levels of free fatty acids in the bloodstream. The heart is highly efficient in utilizing fatty acids through beta-oxidation to generate adenosine triphosphate (ATP).

In the post-absorptive state, the liver increases the production of ketone bodies from fatty acids, which can also serve as an alternative energy source, but the myocardium predominantly relies on oxidizing fatty acids. This preference is supported by the high mitochondrial density in cardiac muscle cells, which are adapted for fatty acid oxidation.

While glucose can be utilized as an energy source, its availability drops during fasting periods, making fatty acids the favored substrate. Amino acids and lactate, although they can be used for energy in specific circumstances, do not serve as primary energy sources for the myocardium in the fasting state. Therefore, fatty acids are established as the key energy substrate for the heart after fasting, reflecting the heart’s reliance on aerobic metabolism and its preference for fatty acids over other substrates.