SNS SQS fanout architecture

Looking at the documentation for this pattern it says

The Amazon SQS message contains the subject and message that were published to the topic along with metadata about the message in a JSON document

So when I publish to an SNS topic, the only properties that are forwarded are the subject of the notification, and the default parameter? Does this mean if I want to send json to my queues I have to stringify it and set it as the default parameter of the notification?