Learn Spanish (Latin America): Se me olvidó que la bebida tiene puras calorías. - I forgot that the drink has nothing but calories.

In Latin American Spanish, placing puro (or its variations) directly before a noun is a common way to express emphatic exclusivity. It means "only," "nothing but," or "entirely." Here, puras calorías emphasizes that the drink is entirely made of empty calories, with zero nutritional value.

Does puras have to match the noun it describes?

Yes. Even though it translates to an adverbial idea like "only" or "nothing but" in English, puro functions as a normal adjective in this structure. Therefore, it must agree in gender and number with the noun it modifies. Since calorías is feminine and plural, we use puras.

Why use Se me olvidó instead of just Olvidé?

Se me olvidó uses the "accidental se" construction, which takes the blame off the speaker by framing the event as something that just happened to them. While you could perfectly well say Olvidé (I forgot), Se me olvidó (It slipped my mind) is the most natural and frequent way to express accidentally forgetting something in daily conversation.

If I am the one who forgot, why is olvidó conjugated in the third-person singular?