If we were designing a energy system to run on either fresh fuel or on stored fuel, before switching to stored, it would call for more fresh fuel. Failing to find more fresh fuel, it would start to switch to stored, while finishing the fresh fuel. It would also start to conserve energy. There is one more twist, short term storage of some rich fuel for quick stoking. This would also start to depleat a bit first, before switching to store.
This implies that before we can expect to burn fat, to any large amount, we need first to pass through hunger. This is not consistent with the "hungry? then eat" concept of today. In the previous times, it was "hungry? to bad, wait until dinner" or the next meal. Not only do we to pass through hunger, but we also need to use up a bit of glycogen. Hunger is just fuel signalling. We should treat it as such, rather than something to avoid.
Do seemingly small changes in philosophy add up to obesity of today? (together with abundance, salesmanship of the food industry, new novel food products, etc.)