Soybeans are an excellent, very-low carb source of both protein and fat. Edamame (green soybeans in the pod) are also good but are't quite as exceptional as a source of protein compared to other beans. Hemp seed and chia seed are considerably more expensive than soybeans for the same amount of protein, but are even lower in carbs. Basically they're zero-carb, if I recall correctly.

My impression regarding lipids (another word for fat) is that vegan diets can be low in Omega-3 and Omega-6 fatty acids unless people pay attention to how much they're getting. From what I understand, some vegan foods like flax seed are technically high in Omega-3, but it's not in a very biologically available form, so it may not be a good source. I've read that ahi flower oil can be an excellent source of biologically usable Omega-3, 6, and 9. It's been a while since I compared it to other potential sources such as hemp seed or chia seed, and I don't remember if those sources provide biologically usable Omega-3.