> it's that that diet / food selection is meaningless as food containing one calorie of potential will always evolve to one calorie's worth of metabolic energy

> it's that that diet / food selection is meaningless as food containing one calorie of potential will always evolve to one calorie's worth of metabolic energy through some metabolic process or another Maybe that's true evolutionarily over tens of millions of years, but it's definitely not true that cellulose calories are remotely equivalent to fat calories -- not unless you're already a ruminant, anyway. Similar issues may present themselves with other types of calories. Just because in theory we could evolve to optimally use all potential sources of energy in food doesn't mean that we actually have yet.