system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that humans need such complex nutrient balances while cows just chill and eat grass all day?
gpt
It's more accurate to think of humans as being able to subsist off a large variety of diets, as compared to cows which can really only subsist off one or two forms. This is partly the reason why humans as a species, like rats, were able to spread across the globe and survive in all kinds of habitats. 
We don't necessarily *need* the complex nutrient balance -- we can live long enough to reproduce and multiply off a narrow diet of whatever we can gather/kill in the near area, but in today's society where most people want to live a maximally healthy lifestyle for 80+ years, the complex nutrient rich diet is advocated.