You can use 'silent push notifications' that are available in iOS 7.0 +. These act in the same way as a push notification but allow your application to run small amounts of code when not loaded. You could set a flag here to tell the app tp update next time its loaded.
Alternatively, like you suggested created a smaller web call that just checks for new content without actually performing a fetch. You could also set these to only first on a specific day of the week/month and time you're content updates with this ?
I guess a combination of these two would cover all bases ?