So it’s about efficiency. A given organism is going to have a particular conversion ratio in terms of how much mass/calories/nutrients whatever you’re measuring it has to take in to increase it’s own content an equivalent amount.

Since the vast quantity of food consumed by animals goes into energy rather than body mass they’re very inefficient. Particularly larger creatures like cows which “waste” (obviously not from the cow’s perspective) that energy breathing, moving, pumping blood, digesting, feeling and so on.

Infants are probably less efficient, as pregnancy is very stressful biologically.