When expressing interest in a certain topic, it's important to have a varied vocabulary to avoid repetitive language. Synonyms for the phrase "be interested in" include "be fascinated by," "be intrigued by," "be absorbed in," "be engrossed in," "be captivated by," "be enamored with," and "be hooked on." Each of these phrases captures a different level of engagement and enthusiasm, allowing for a more nuanced expression of interest. Additionally, using synonyms can make your writing or conversation more engaging and precise, helping you to convey your thoughts and feelings effectively.