They are not themselves essential, but variety is essential. We don’t know enough about what the human body actually needs to say with certainty that any restricted subset is definitely good for your long term health.
As for protein sources, I believe soy is the cheapest source around these parts. Next up is chicken, then various beans. So you would be right that the cheapest proteins where I’m located are vegetables, and it’s also a complete protein and very tasty, but soy allergies are very common, so you can’t expect everyone to live off soy. Beans have the problem of being incomplete (can be paired with grains to make them complete), and are quite a bit less dense so you need to eat a lot to get the same nutrients, often more than your stomach can hold.
They are not themselves essential, but variety is essential. We don’t know enough about what the human body actually needs to say with certainty that any restricted subset is definitely good for your long term health.
As for protein sources, I believe soy is the cheapest source around these parts. Next up is chicken, then various beans. So you would be right that the cheapest proteins where I’m located are vegetables, and it’s also a complete protein and very tasty, but soy allergies are very common, so you can’t expect everyone to live off soy. Beans have the problem of being incomplete (can be paired with grains to make them complete), and are quite a bit less dense so you need to eat a lot to get the same nutrients, often more than your stomach can hold.