The A.V. conveys the sense of having an opinion, thinking. But the point is the strength or weakness of the man's faith (see Rom 14:1) as it affects his eating. Hence Rev., correctly, hath faith to eat.
Herbs (λάχανα)
From λαχαίνω to dig. Herbs grown on land cultivated by digging: garden-herbs, vegetables. See on Mar 4:32; see on Luk 12:42.