Greens against cancer

Gotta love those greens. Per the women of the Iowa Women's Health Study, those in the highest quartile of greens consumption had less than half the ovarian cancer risk of those eschewing greens.

But there's the problem, how to cook the greens so you can chew them? A patient of mine says boil them for 2 and 1/2 hours. She favors turnip greens, or green turnip green pudding after cooking that long. After all that cook cook cooking, is there any goodness left for the fight against cancer?