How are animals that eat only one kind of food not horribly malnourished? Do they need a narrower set of nutrients than humans?

Question

How are animals that eat only one kind of food not horribly malnourished? Do they need a narrower set of nutrients than humans?

In:

Answer 1

Animals (including humans) are able to synthesize some of what their bodies need, and the things the body can’t produce on its own need to be directly ingested.

An example is vitamin c. Humans don’t produce it, so we need to eat it to avoid nasty things like scurvy. Cats and dogs need it, but their bodies can self-produce the needed amount, so they don’t need to consume any from food.

To be fair, I don’t know much beyond that, but I’d guess that animals that subsist on very narrow diets probably have a combination of relatively minimal nutritional needs (in terms of mineral/vitamin diversity) and the ability to synthesize whatever different things they do need.

edit: adding some additional info, inspired by several of the other comments below and elsewhere to the post. Also added a couple “just ok” links, which do provide some jump-off points to better sources.

“Narrow diets” might not be as narrow as they seem to us. For example, whereas humans tend to eat mainly muscle tissue (mostly protein), carnivorous animals eat muscle + organs, which provides a lot of nutrition. Also, surviving != thriving. [link](https://www.scienceabc.com/eyeopeners/if-human-health-requires-a-balanced-diet-how-do-animals-survive-on-such-narrow-diets.html)

Similar to the synthesis concept I mentioned, is a more symbiotic approach, such as that in cows. Cows eat a lot of grass, yet are able to meet their protein and nutritional needs. Their four chamber stomachs break down the grass more completely than ours, and hosts bacteria that feed on the grass as this happens, and the cow in turn ends up deriving nutritional value from the bacteria. [link](https://medium.com/a-microbiome-scientist-at-large/how-does-a-1-200-pound-cow-get-enough-protein-506797b53845)

In summary, it seems like the main reasons animals get by how they do is because: they’re still here. They’re either specialized to process their diets, and/or we’re ignorant about what they’re actually getting in their diets.