iOS7 update - it reset all my emails to unread

I updated my iPhone 5 to iOS7 today but it reset all my emails in the Mail app to being unread, even the ones not downloaded to my phone. How can I change it so it only thinks new emails are unread? I know about the 'Mark All' then 'Read', but that only does a handful of messages at a time. It thinks all the emails in my account - thousands of them - are unread. Since the phone only fetches a certain number of emails at a time, it would take forever to fetch them all to my phone, and I don't want all of them locally anyway.

Thanks!