system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why do humans need to eat many different kind of foods to get their vitamins etc but large animals like cows only need grass to survive?
gpt
In addition to the 'efficiently breaking down grass' thing, and the 'they eat a variety of plants' thing, there's also the fact that species typically evolve the ability to make vitamins that they can't get easily in their diet. For example, humans make vitamin D because there aren't many food sources of it, but we can't make vitamin C, but can find it in food. But other species can make their own vitamin C.

It's a trade off between needing to find a variety of food and not needing the cellular machines to make more stuff.