What bajantara said. I usually find that it takes at least 5 feedings at the food bin before the status bar moves.

Farming or Healing (or even Breeding if you can afford the extra babies) are the best "occupations" for him to regain his health. But you need to be patient, it'll happen slowly.

If you don't need to watch your game for other things, shut it off for a while. Villagers tend to keep "on task" more when the software "catches up" with realtime. After you have it off for 10-20 (or more!) minutes, and then start the program again, you can peek at the log file and see the progress. You should be able to see log entries where he is slowly healing. (The log won't be 100% caught up, you'll need to quit the game again to see the whole thing.)