Why can't the brain and red blood cells use fuels other than glucose?

Question

The question is rather straight forward: I have always been curious as to why, but cannot find an explanation online.I can imagine that the mechanism is different for each, but **why does brain tissue and red blood cells use specifically and only glucose for energy metabolism?**

Answer 1

i believe the brain can use ketones for energy, but does so only in extreme cases where glucose is unavailable. red blood cells can only use glucose because they do not have mitochondria