system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why is eating enough protein considered to be crucial in order to build muscle as human while a lot of animals with huge muscles in fact don't eat any protein?

Depending on the source you are being told that you need to eat 1.5 to 2 grams if protein per kg of body weight / 0.8 - 1grams of protein per lbs of bodyweight. Protein sources are meat, fish, nuts and oats and milk and it's products.

Now have a look at elephants, rhinos and even gorillas as they are somewhat similar to human. They eat grass, plants and fruits. This nutrition provides little to zero protein. How can these animals maintain and even build their muscles?
gpt
Protein and the building blocks of protein exist in plants, but human tummys are not super efficient at acquiring them. We also can't eat a lot of food without getting sick. Herbivores have digestive systems that are designed to breakdown plant material and are much better at acquiring those nutrients than we can. This is why cows have several stomachs and herbivores have longer small intestines than carnivores. They also eat a far larger volume of vegetation than what humans could manage.

On top of that, most herbivores will actually eat meat when they can get it.