Humans are omnivores, and their diets are different from those of herbivores. The two cannot be compared. Grass can't even be digested by humans. Don't mention herbivores, just that they are all mammals. Can people chew bamboo every day like pandas? Obviously not.

Protein is a necessary place to repair muscle injuries caused by sports or labor, so the growth of muscles needs protein, and the increase of muscles cannot be separated from protein.

If protein's intake is insufficient for a long time, fitness will not have sufficient effect.

Many foods contain protein, not only protein powder contains protein, but also meat, eggs and milk contain protein, but bean products such as tofu are rich in protein.