In the context of human energy use it’s also extremely simplified. Energy in can be measured in terms of food, but that assumes all calories are absorbed. It also assumes exact efficiency. It assumes average energy use etc.

As weight loss drugs show, for many who struggled with weight loss before, it’s also important how the body uses, stores and distributes the energy.

Sure, no energy is created or destroyed, but dietary makeup, hormones, metabolism gut motility, gut biome, etc all have an effect in the process.