I tried to use the list thread method:
GET https://www.googleapis.com/gmail/v1/users/{MyEmailAddress}/threads?labelIds=INBOX&labelIds=UNREAD&key={YOUR_AP
The Gmail API now provides total and unread counts for messages and threads on each Label using the Labels.Get() method. See: https://developers.google.com/gmail/api/release-notes and https://developers.google.com/gmail/api/v1/reference/users/labels