I don't think anyone here would say that you HAVE to eat animal protein. Like many others here, I was a vegetarian (never vegan) when I was younger. I was also pudgier than I am now.

We don't make our own amino acids from carbs but we can combine component amino acids in incomplete proteins to make complete protein. Unfortunately most of those incomplete protein sources are also significant sources of carbohydrates which many of us cannot handle. Good luck!