Learn Spanish (Latin America): No soy ni vegano ni vegetariano, pero como muchas verduras. - I am neither vegan nor vegetarian, but I eat a lot of vegetables.

In Spanish, if a negative word like ni comes after the verb, you must put a no before the verb. This double negative is required! If you translate it literally, it sounds like "I am not neither vegan nor vegetarian," but in Spanish, this is the correct and natural way to say it.

Could I drop the first ni and just say No soy vegano ni vegetariano?

Yes, you can. Saying No soy vegano ni vegetariano simply means "I am not vegan or vegetarian." Including the first ni makes it ni vegano ni vegetariano, which specifically translates to the correlative "neither vegan nor vegetarian," adding a bit more emphasis to your statement.

Why aren't we using un here, like No soy un vegano?

When using the verb ser to state a general category you belong to—like a profession, religion, nationality, or in this case, a dietary lifestyle—Spanish drops the words un or una. You would only add the article back in if you included a descriptive adjective, like No soy un vegano estricto (I am not a strict vegan).

What is the difference between verduras and vegetales?