The last thing I would put in a smoothie....is Kale. Unless being poured on a USF fan, then it is worth it because it is being tossed. This reminds me of Edgar Friendly's rant about the future having 47-year-old virgins drinking Banana Broccoli milkshakes...
If you think Kale tastes better than Spinach, then you have burned out your taste-buds by licking a hot pancake griddle, or too many boiling cups of coffee. (I know, I know...it's a matter of preference, a matter of taste, yada yada yada...so is eating dung).
Want more nutrients? Then eat more spinach.
Recent studies show that the difference in nutrient value is minimal when compared/contrasted. Vitamin C is higher in Kale leaf for leaf. But spinach has more Iron, is easier to digest and is actually much easier to cultivate. Therefore, yes...Kale is a fad veggie. Even Native Americans tossed it aside in favor of Spinach, which is why, historically, spinach is more popular.
So, want to match Kale's nutrients? EAT MORE SPINACH!
Pop-eye eats SPINACH...not Kale...because Kale blows donkey nut.
http://skipthepie.org/vegetables-and-vegetable-products/kale-raw/compared-to/spinach-raw/