Your analogy is different from the situation we're presented with here.
The question I answered is why converting to kcal is nonsensical. Yes it's just a different unit but... Kcal is nowadays used for things you eat (and exercise because it makes sense to use the same unit), it doesn't really make sense to convert radioactive material to that unit.
"If humans had the ability to perfectly extract energy from gasoline/nuclear fuel then how much would we need to survive a week?"
Saying "no you can't eat gasoline" would be a pointlessly pedantic answer.