This is true, oxalic acids are natural compounds that spinach and certain dark greens like chard produce that help protect the plants. They are not in high enough quantities to be harmful but they will interact with calcium absorption. Cooking is one way to decrease oxalic acid content. Also rotating your greens in another great way to still enjoy your Blasts and not worry about oxalic acids. When you rotate your greens, you are rotating your exposure to different nutrients in different foods. You may not absorb all the calcium in your Blast when you have spinach but you are getting good sources of iron, antioxidants, vitamin k and b vitamins. If you use romaine lettuce the next day, you will receive a new amount of nutrients like calcium and phytonutrients. As long as you rotate your greens and get a balanced diet, you will absorb all the nutrients your body needs.