Humans don't eat electricity or oil. Sure, they may be used to increase yields of harvests, but the limitation is still how fast plants grow and how much area they need.
Effectively we do eat oil. We replenish soil fertility with fertilisers made with oil energy, we farm large areas with machines powered by oil, etc. etc. We grow more plants faster, with shorter turn-over times, and use less human effort to do so, thanks to oil. There might be a few intermediaries but the end result is that energy from oil ends up converted into human biomass. I can guarantee you if we had never discovered oil there would be far fewer people, with far slimmer waistlines.
"is that energy from oil ends up converted into human biomass"
No, that's the whole point!
Humans surely cater to farming using oil, and we would be a lot worse without it.
But in the end food came from two sources: energy from the sunlight and CO2 (matter) from the atmosphere. (Well, then we could say we're eating car emissions).
Unless you're converting oil directly into food (let's say carbohydrates), no, all energy from plants comes from solar energy. You could of course have a giant oil powered lamp that produces light and shine that over the crop.
