When there is low blood glucose levels, oxaloacetate is converted to pyruvate, and ultimately to glucose. This leads to a state where there is not enough oxaloacetate available and acetyl CoA, produced by beta oxidation, cannot be utilised in the citric acid cycle. Instead, acetyl CoA is diverted to the production of ketone bodies. Ketone bodies are used as an energy source in this case as compensation for the low blood glucose. This is so because it produces acetyl CoA which is used in the citric acid cycle.
My question is how can ketone bodies use acetyl CoA for energy if there is low oxaloacetate in the first place? Surely, ketone bodies have no energy benefit compared to fatty acid beta oxidation, if both use the same pathway to produce energy.