system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If humans need such a balanced diet to stay healthy, how is it that most animals seem to get away with having a very narrow diet?

Maybe I am naive in the diet of animals but it seems to me that when you think of, say an owl, we all know that owls eat mice.  If humans were to eat just one food like that it seems to me that we would not get enough nutrients to live.  How do animals get all their nutrition?
gpt
Very few animals have extremely narrow diets, and animals tend to eat things that we don't. For example, carnivores will eat organs and entrails, while most of the time humans throw these out. Those organs often are packed with nutrients which are almost impossible to find in muscle tissue, which is most of what we think of as "meat". Plant eaters usually eat a lot more by volume and often have lots of helpful microbes in their gut to help digest their food. 

It is possible to stay alive on a very limited diet. It's healthier to eat more whole foods and get a broader range of nutrients. Also, eating "just one food" is a little misleading. If that one food is whole cooked potatoes, you can probably survive indefinitely. If that one food is white bread, you'll suffer from metabolic issues due to a lack of essential nutrients (white flour is made by removing the most nutritious parts of the grain, so it's missing a lot of good stuff)