Why does the brain use ketone bodies as metabolic fuel during starvation when th

When triacylglycerides are broken down by various lipases in fatty acids, they are insoluble in water due to their hydrophobic tail. Thus, they are transported in the blood by various proteins, including serum albumin. The blood-brain barrier is very specific on the types of proteins it allows to pass from the circulating blood to the interstitial fluid. For instance, cells of the bar-rier actively transport metabolic products such as glucose across the barrier with specific protein. However, since it generally excludes proteins from entering the cerebrospinal fluid, it limits the efficiency of delivering an amount that is sufficient for adequate energy production via beta-oxidation. Ketone bodies, which include acetone, acetoacetate, and beta-hydrobutyrate are hydrophilic (water soluble) and are generally small molecules that can pass through certain transporters of the cells lining the blood-brain barrier through specific transport systems (i.e. carrier-mediated transporters, receptor-mediated). This is why the brain uses ketone bodies to harvest energy, simply due to the fact that they are more attainable.