Add a Twig filter for CraftCMS templates to "prune" out fields of entries.

1. Move the prune directory into your craft/plugins directory.
2. Go to Settings > Plugins from your Craft control panel and enable the prune plugin

The primary reason for this is to control the fields being output to json_encode.

{{ craft.entries.section('news').find() | prune(['title', 'body']) | json_encode() | raw }}

The above template will get all entries from the "news" section, grab just the title and body fields from each, and then output it to JSON.