Yes. And the efficiency of "food calories - shit calories" varies wildly between individuals and across time for individuals. The number of calories you see in

Yes. And the efficiency of "food calories - shit calories" varies wildly between individuals and across time for individuals. The number of calories you see in a food database is calculated based on how well a few macronutrients literally burn in a lab setting. All it tells us is a way to compare input values, not usage or output.