alt Hacker NewsChickens will eat grain, but the best eggs (and healthiest chickens) come from lots of protein and green leafy matter. Vermiculture and simple insect attraction methods like maggot buckets, food scraps, and lawn/garden waste can go a long way with chickens.
I don't think they get a lot of calories out of greens, do they? I feed mine all sorts of scraps, but they also eat a lot of grain.