The two most common most talked about dark green leafies, both are fantastic for you nutritionally, so fantastic in fact that comparing them in general health is almost irrelevant so how about in terms of antioxidants(?)!

This time I had to pull up a different study entirely which instead of covering just a few hundred foods it covers over 3000! Sadly it doesn't cover many leafy greens, so I couldn't compare these two to collard greens or swiss chard, but hey, it's something.

So which one IS better?

As you can see Kale has about 2x as much antioxidants as Spinach, and if you get some fancy red kale that may even be 4x as good!

But hey, they're both so great for you it's not a big deal to eat one or the other if you prefer one over the other, but no matter what with how nutritionally dense and generally amazing dark green leafies are for you you should probably get some more in :)

On a side note look how cool "red" kale looks~

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To see all the foods and how they compare see the science once again, or wait for my next post on the subject.
Currently I've made two other posts like this, one for Tree nuts and one for Apples, so if you're curious, check'em out :)

The only image not from the science that I used, the Kale vs Spinach one was sourced from here
Opps I forgot the kale

Also, a big thanks to @full-measure for the request for one of these on (dark?) leafy greens, sorry I couldn't find any sources that included more variety, but it's rare they test these things. Swiss Chard & Collards are probably somewhere in the middle though based on their colors, genus, etc.