Dark, leafy greens, like kale and spinach, are considered to be some of the healthiest, most nutrient-dense foods on earth. They provide high levels of antioxidants, and an impressive amount of vitamins and minerals. We definitely want to include as much of them in our diets as we can.
Did you know, however, that they actually become more beneficial when gently cooked? That's because the nutrients become more absorbable by the body. Steaming it or gently sautéing it for just a minute can improve its nutrient absorbability while not destroying its antioxidants and phytochemicals.
Leafy greens (spinach, in particular) are extremely high in oxalic acid, that is reduced with cooking. The problem with oxalic acid is that it binds with minerals, like calcium, magnesium, and iron, and does not allow them to be absorbed by the body. We are already generally deficient in these minerals, so we want to avoid furthering this problem. When the oxalic acid binds with these minerals, it also causes them to crystallize, which can damage tissues, and cause kidney stones and inflammation in the body.
In addition, kale belongs to the cruciferous family, and can be difficult to digest when raw. It can also suppress the thyroid because it is a goitrogenic vegetable and, when raw, can inhibit the uptake of iodine by the thyroid gland if eaten in excess. (Source: Chris Kesser)
Now, I'm not saying that you should never eat a raw kale or spinach salad. I certainly don't intend to give them up. However, when eating a lot of these healthy vegetables (as we should be!), it's best to limit your raw intake of them.
The problem is that most of us probably will not put warm steamed spinach in our smoothies every day. Yuck. Even if the thought of it didn't disgust you, the effort of it would be a deterrent. Smoothies are supposed to be quick and easy. I certainly don't need another step! Not to mention, smoothies are such an easy way to pack a big nutritional punch, and I don't want to get less of these superfoods in my diet!
So, here's the easy solution: I have started steaming and freezing my greens to throw in my smoothies, rather than putting them in raw. It's easy if you just do it ahead of time and freeze them.
Here's how I do it:
First, steam your greens for about a minute or two. I do this by filling a pot partway with water and bringing it to a boil. Then I add a basket on top and stuff it full of spinach and kale and put the lid on top. Steam for 1-2 minutes and remove from heat.
Next, scoop out greens using a 1/3 or 1/2 cup measuring cup onto a baking sheet covered in unbleached parchment paper. They will come out as spinach "pucks" in the shape of your measuring cup.
Put the baking sheet in the freezer. When the pucks are frozen, transfer them to a storage bag or container to keep in the freezer. Do large batches at a time so that you have them on hand and ready to go. Then, you can easily grab one to throw in your smoothie! That's all there is to it!