This song is about lead singer Trace Cyrus' ex girlfriend, Hannah Beth. The lyrics, "How does it feel to trade my trust for a touch?" refers to her cheating on him, which is the reason they broke up.
Meghan Trainor and her producer Kevin Kadish originally wrote "All About That Bass" for another artist to record. However, after Epic Records boss LA Reid heard Meghan play a demo of the song on a ukulele, he signed the young songwriter to his label and told her she should sing it.