I saw in the Upgraded Chef book Dave has Raw Spinach, Kale, and Collards in the red area (green area if cooked). Has he said in his podcasts or elsewhere why this is so?
They block calcium absorption when raw. Here is one reference:
I steam my kale and collards now for about a minute then load them up with butter. I find it to be much tastier with very little extra prep and clean up time. It is well worth it.
Also oxalic acid (particularly bad for women).
I thought this was only true for spinach, not kale/collards?
Nope, it's everything dark and leafy (the stuff that is great for you). Quoted from that article:
Oxalate occurs naturally in many common plants, especially rhubarb and dark leafy greens such as spinach, chard, beet greens, and kale. Itâ€™s present in lesser amounts in other vegetables, fruits and nuts.
I still throw the steamed stuff in my salads, it makes it more dense anyhow and my lunch container doesn't need to be huge.
kale has a rather miniscule amount: http://www.nal.usda.gov/fnic/foodcomp/Data/Other/oxalic.html
i thought it was more about thyroid suppression than blocking calcium absorption