Spinach Can Hinder Calcium Absorption; Here’s How To Make Sure It Doesn’t

Call me Popeye (or maybe Popette?), because I’m absolutely obsessed with spinach. I eat it constantly, cooked and raw, in everything from nachos to pasta to salads to hummus. The other day, I tweeted about my deep, abiding love for the leafy green and one of my friends replied to my tweet, saying that eating large amounts of spinach can actually interfere with the body’s ability to absorb calcium. Wait, what? This was news to me, as I always thought spinach was hands-down one of the healthiest foods you could eat. Confused, I did a little research, hoping my love for my favorite vegetable wasn’t actually harming my health. I didn’t find much information, so I took my question to the experts. Here’s what they had to say about the science of spinach and calcium absorption.

Registered dietitian Mary Hartley explained that oxalate, a pesky little molecule that binds to the calcium in spinach, leaves only 10% of the essential mineral available for absorption:

Oxalate occurs naturally in many common plants, especially rhubarb and dark leafy greens such as spinach, chard, beet greens, and kale. It’s present in lesser amounts in other vegetables, fruits and nuts. Oxalate binds with calcium in the digestive tract to form an insoluble salt that cannot be absorbed. For instance, one would have to eat 15.5 cups of raw spinach to match the level of calcium absorbed from one cup of milk. Oxalates do not significantly impact calcium absorption except when levels are high. Still, it is important to remember that dark leafy greens are not an important source of calcium in the diet.

Uh oh. Bad news for vegans who rely on leafy greens as a large source of calcium.

Dr. Bess Stillman, integrative medicine consultant and practicing ER physician in New York City, told me more about spinach specifically, and its role in a healthy diet:

In addition to the vast array of cancer fighting anti-oxidants and flavanoids, research has shown that a compound called ”glycoglycerolipids,” found in the spinach leaf, can prevent damage and inflammation to the lining of the stomach—meaning a healthier digestive tract that’s better at absorbing the nutrients you need to feel energized and healthy. Spinach also is a fantastic source of iron, making it an especially important food for both vegetarians and women, who often need iron to help replace blood lost during their monthly periods.

Whew. No need to panic (or cut spinach out of your diet). Dr. Stillman comments that, “in the case of spinach, it’s all about how you eat it.” Here are her suggestions on how you can cook spinach so you can get the maximum nutritional benefits of the little green leaf:

  • Cook It: Lightly cooking spinach will also breakdown the oxalic acid molecules without causing you to lose too many of the vital nutrients—try steaming, sauteeing or blanching, which also increases the amount of vitamin K available. Pour some extra virgin olive oil into a pan on low to medium head and sautee lightly until the leaves begin to wilt.
  • Eat With Citrus Or Tomatoes: The Center for Disease Control and Prevention recommends eating spinach with citrus or tomatoes. These foods are high in vitamin C, which changes the form of iron in spinach to the easily absorbed kind you find in steak–but with much fewer calories or risks to your health. Vitamin C also blocks the oxalate from binding to calcium, encouraging further absorption. Try adding spinach to your pasta sauce, or make your BLT a bacon spinach tomato sandwich. Toss with orange muscat vinagrette and enjoy absorbing both the flavors and the nutrients you want.
  • Buy Organic: Remember, spinach is one of the “dirty dozen” foods, which have high pesticide residue. To get the most out of spinach’s health benefits, buy organic.

Photo: Shutterstock

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    • Patricia

      Just to clarify….was Dr. Stillman saying that consuming Vitamin C with your raw spinach can effectively offset the oxalate-calcium binding? For those of us who love a big spinach salad, it’s not difficult to make sure that there’s also lots of Vitamin C in the meal. I’d sure hate to think that all that calcium is going to waste….. :(

      • Carrie Murphy

        Patricia, yes, that’s pretty much the gist of it!

    • Dr. Bess

      While vitamin C doesn’t make 100% of the calcium in spinach available it allows you to absorb vastly more than you would without it’s addition to the meal ( it makes the iron more available to your body too)Keep in mind that the vitamin C needs to be consumed at the same time as the spinach to be effective.If you have any more questions about this or other nutrition and health issues that you read about on Ms. Murphy’s blog or elsewhere, feel free to ask at drbstillman.wordpress.com (my name in the article is a link)

    • moringa-seeds.com

      Nice information. The world’s most nutritious tree ‘Moringa leaf’ contains approximately 20 types of amino acids, 46 types of antioxidants, 36 anti-inflammatory compounds – All natural 90+ nutrients make for the best natural nutritional supplement. It is a tremendous source of bio-available vitamins and minerals like Vitamin A, Vitamin B, Vitamin B1, Vitamin B2, Vitamin B3, Vitamin B6, Vitamin C (Ascorbic Acid), Vitamin E and Macro Minerals, Trace Minerals, Phyto nutrients. Moringa leaves are a good source of bio available quality protein & dietary fiber

    • ronald moris

      It is also very important to eat a good amount of vitamin C, to better absorb iron from the spinach


    • Patricia

      Carrie & Dr. Bess: Thanks so much for your responses!

    • Doreine

      will blenderizing breakdown the oxalic acid molecule?

    • Bob

      I was concerned that I eat too much calcium as it can cause calcification issues with cardiovascular system and the brain, about 2x to 3x RDA through mostly fortified milk for protein purposes, I also by chance eat spinach regularly so hopefully they balance each other out.

    • Raq

      Oxalates also inhibit non-heme (plant based) iron absorption so it is ironic (no pun intended) that eating an iron-rich plant like Spinach can actually inhibit iron absorption. It is recommended that you consume spinach with something that increases iron absorption, i.e. vitamin C. If increased iron intake is really important to you, lightly cooking spinach releases oxalates, which allows more iron to be absorbed. Additionally, cooking in cast iron cookware increases iron intakes but remember intake and absorption are two different animals!