"You like food."
Translation:Is maith leat bia.
When trying to translate the verb "to be" into Irish, you have to choose between two forms, the copula is and the verb bí. In that case, you decide whether your "to be" is "introduce someone or something" (not the most useful description of an chopail, IMO).
You're not trying to translate "to be" into Irish in this case, so you don't have to decide whether to use the copula or bí, therefore the "introduce someone or something" determiner is of no relevance.
"love", "like", "hate", "adore" etc are all verbs in English. In Irish you use the copula with a noun or an adjective and the preposition le to translate those verbs. That's just the way Irish expresses those types of verbs.