By mass, there’s relatively little carbon in living organisms and on earth

Some quick googling tells me about 60% of our body is water, and of what is left, almost half is carbon. This would include all of the fats, carbohydrates and sugars that we need for energy.

If you ate a non-carbon based lifeform, you might get some water or iron and other minerals you need a little of in your diet, but the reason we need to eat so much is to ingest different forms of carbon to digest.

An alien that died on earth would probably not even rot because our food chain is so dependent on our proteins.