He usually eats sesame seeds and carrots because of their antioxidant contents. -- You wouldn't really ever say "elixir of youth" in a normal context.

Thank you very much.

The sentence doesn't make any sense as written. I can't ignore the context of what 'elixir of youth' means. I don't see the point of giving you a grammatically correct sentence that nobody would ever say, and that doesn't make sense. The only way it would work is if elixir of youth were the name of a particular product, like a cream or a lotion made by a company such as LOréal or something. Then you could say 'He usually takes 'Elixir of life' (in quotation marks to show it is the name of a product) which contains lots of antioxidants.

Thank you very much for your information, Paul. Let's imagine the 'Elixir of youth' is real and exists. I'd like to know about the sentence I wrote in my question. Especially the word 'Has' and 'As elixir of youth'. Is it correct to say 'He HAS them AS elixir of youth'?

Elixir of life/elixir of immortality/elixir of youth are all sometimes used to describe this kind of thing.