Alicia Mackey Huber warns that green smoothies with high-oxalate greens can bind calcium into harmful crystals. A typical smoothie contains about 1 gram of oxalate, roughly 20% of a lethal dose. Some people have lost kidney function after green-smoothie cleanses. Safer options use low-oxalate greens like arugula and cucumbers.
If you drink green smoothies, just stop. Unless they're made with things that don't have oxalic acid. Calcium would be there to form the crystals in the drink instead of in your blood vessels, and it might help a little bit, but they're still really, really rough on you. It takes about 5 grams of oxalate to kill people because of kidney damage, and a green smoothie can have a gram, like 20% of a lethal dose. And there are people who have lost kidney functions from green smoothie cleanses. So you just have to be careful. What's in there. I'll drink something green. If it has arugula and it has cucumbers, those are general safe green apple juice, if you're into that kind of stuff. But you really want to be careful for the oxalic acid stuff.
