If you get a safe amputation and keep the limb, is it legal to eat it? ?

I know this is an odd thing to ask so bear with me. So my friend and I were talking about cannibalism and we know it's illegal but we got into the discussion of if it's okay if the person willingly gives someone else their limb to consume. He keeps saying that it would be illegal to eat any part of a human being even if the person who is giving the limb is perfectly okay with it. I think it wouldn't be illegal as long as it's safe and consensual. I just wanna know which is right.