This is a function of higher mind; awareness, you have everything you need I would go with instinct. Science will never be able to explain how this works, just abandon all hope of scientific rescue. You have everything you need within.
You're describing magical thinking. As a counterpoint you can look at the problem of scurvy on per-industrial naval voyages. They didn't have an instinct to eat citrus, it was discovered by a long and painful period of trial and error. As another counterpoint, historically "rabbit starvation"[1] otherwise know as protein poisoning has been an issue periodically. If people innately felt the need to consume fat in particular this wouldn't happen.
