Spinach has been my go-to green for years now. The taste is simple, it’s easy to chew when it’s raw, it blends seamlessly into green smoothies, and it’s high in blood-strengthening iron.
Well, apparently spinach, along with it’s friends chard and beet greens, are also high in a little chemical called oxalic acid.
What is oxalic acid, and why does it matter?
I’m not sure how, but even after four years of nutrition courses, oxalic acid has never crossed my radar until just recently. This little guy is naturally contained in many of our foods, especially spinach, chard, beet greens, parsley, and rhubarb, and can prevent the calcium from being fully absorbed by the body.
Oxalic acid binds to the calcium in these foods, forming a compound called calcium oxalate. Instead of being absorbed into the bloodstream, calcium oxalate is mostly removed from the body along with other toxins. This is especially true with foods high in fiber.
If too much calcium oxalate is formed in your body, you can develop a fun little guy called a kidney stone! Yup. That is where kidney stones come from. If you’ve ever experienced one of these (thank the Lord, I haven’t!), you know the excruciating pain that is involved in passing it. Fortunately, this usually only occurs when a person consumes a very large amount of calcium, especially from dairy products. (If you needed yet another reason to avoid dairy…)
Large quantities of oxalic acid are actually poisonous. We don’t consume the leaves of the rhubarb plant, because they contain enough oxalic acid to make you quite ill. If you consumed many pounds of these leaves you could even die. However, the quantities contained in normal food sources will not make you sick.
So, I should never eat spinach or chard again?
Yes, I know, I have posted quite a few recipes that include these greens, including one this past week, and it is certainly still safe, and even desirable, to eat foods that contain oxalic acid. These greens contain many other nutrients that are incredibly good for you. I would just recommend not making them the primary greens in your diet, and certainly not your main source of calcium.
According to most of the studies done on the effect of oxalic acid on calcium absorption, while the effect is certainly there, it may not be as extreme as it is often made out to be. The difference in absorption is notable, but not statistically significant, and is much more prevalent in studies done on rats than in studies actually performed on humans.
As a general recommendation, keeping spinach/chard/beet greens to about a third of your total green consumption is advisable. Eat them on occasion, but don’t pack your green smoothie full of them every single day. Cooking these foods can also help to break down the oxalic acid, helping to retain more of the calcium. As with all things nutritional, the effects of oxalic acid really vary by person; some people may be more affected than others. Those at risk for osteoporosis, such as older women, should be the most particular about decreasing their oxalic acid intake.
It has been noted that oxalic acid only seems to bind the calcium within the foods in which the acid is present. Calcium from other foods eaten alongside will still be absorbed normally. There are plenty of other great plant-based sources of calcium out there, including Brussels sprouts, kale, collard greens, broccoli, bok choy, watercress, mustard greens, cabbage, hijiki, almonds, tahini, white beans, and tofu. Take a vitamin D supplement, or get plenty of sunshine, to further increase your calcium absorption.
This is still a fairly new concept to me, so if anyone has any other information on oxalic acid, please feel free to elaborate in the comments section. I would love to hear what you have to say on the subject!
What is your favorite plant-based calcium source? Have you heard of oxalic acid?