Why Spinach's Calcium is Not Easily Absorbed
Spinach is a nutritional powerhouse, packed with vitamins A, C, and K, as well as minerals like magnesium and iron. It also contains a substantial amount of calcium. However, much of this calcium is not easily absorbed by the body due to a naturally occurring compound called oxalic acid, or oxalates. These oxalates bind to calcium during digestion, forming calcium oxalate, an insoluble compound that the body cannot easily absorb. This means that while spinach has calcium, a significant portion of it is unavailable to you. A study found calcium absorption from spinach was only about 5.1%, compared to 27.6% from milk.
The Best Foods to Pair with Spinach
The key to maximizing calcium from your spinach is to introduce other high-calcium, low-oxalate foods into the same meal. This provides your body with a separate, readily available source of calcium that the oxalates won't bind to.
Dairy Products
Dairy is an excellent choice for pairing with spinach as it contains high levels of easily absorbed calcium and no oxalates.
- Milk: Add milk to a creamy spinach sauce or use it in a baked spinach gratin.
- Cheese: Incorporate cheeses like mozzarella, fontina, or parmesan into baked spinach dishes.
- Yogurt or Kefir: Blend spinach into a smoothie with Greek yogurt or kefir for a calcium boost.
Calcium-Fortified Foods
For those on a dairy-free diet, fortified alternatives are a great way to ensure adequate calcium intake.
- Fortified Plant Milks: Use fortified soy, almond, or oat milk in spinach recipes.
- Calcium-Set Tofu: Tofu that has been set with calcium sulfate is a fantastic calcium source. Add it to spinach stir-fries.
Low-Oxalate, Calcium-Rich Vegetables
Since spinach is high in oxalates, rotating your leafy greens is a smart strategy.
- Kale: Contains ample calcium with much lower oxalate levels than spinach.
- Bok Choy: Another leafy green with a good calcium profile and lower oxalates.
- Broccoli: A reliable source of calcium that pairs well with spinach in many dishes.
Fatty Fish with Bones
For a savory, mineral-rich pairing, canned fish with edible bones is an exceptional option.
- Sardines and Canned Salmon: The bones in these fish are a powerhouse of calcium. Add canned sardines or salmon to a spinach salad or pasta dish.
The Supporting Cast: Nutrients for Absorption
For the body to properly utilize calcium, other nutrients are needed. Vitamin D and magnesium are particularly important.
- Vitamin D: Crucial for regulating calcium balance and absorption. Sources include fatty fish, egg yolks, and fortified foods.
- Magnesium: Helps convert vitamin D into its active form, essential for ensuring calcium is deposited in bones. Seeds, nuts, and legumes are good sources.
Cooking Methods to Reduce Oxalates
While pairing is the most effective strategy, how you prepare spinach can also make a difference. Blanching or boiling spinach can significantly reduce its oxalate content, as the compounds leach into the cooking water. Studies show boiling may reduce oxalates more effectively than steaming. It is important to discard the cooking water after boiling to remove the leached oxalates.
Spinach vs. Other Calcium-Rich Greens
| Feature | Spinach (Cooked) | Kale (Cooked) | Broccoli (Cooked) |
|---|---|---|---|
| Calcium Content (per cup) | ~123 mg | ~89 mg | ~60 mg |
| Oxalate Level | Very High | Low | Low |
| Calcium Bioavailability | Low | High | High |
| Best For Absorption | When paired with other calcium sources | A standalone source of highly absorbable calcium | A standalone source of absorbable calcium |
Recipe Ideas for Enhanced Absorption
- Cheesy Spinach and Ricotta Bake: Combine spinach with calcium-rich ricotta and mozzarella cheese for a decadent, nutrient-dense meal.
- Sardine and Spinach Pasta: Toss canned sardines with olive oil, garlic, and blanched spinach for a quick and easy dish. Adding a sprinkle of parmesan cheese boosts the calcium even further.
- Dairy-Free Spinach Smoothie: Blend blanched spinach with fortified oat milk, a banana, and a tablespoon of tahini (made from calcium-rich sesame seeds).
- Egg and Spinach Scramble: Scramble eggs with cooked spinach and feta or goat cheese. The vitamin D from the egg yolk helps with absorption.
- Spinach Salad with White Beans: Add cooked white beans and a vinaigrette dressing to a raw spinach salad for a boost of calcium and magnesium.
Conclusion
To get the most out of your spinach's nutritional profile, especially its calcium, it is essential to be aware of how oxalates function. Instead of counting spinach as your primary calcium source, incorporate low-oxalate, high-calcium foods into your meals. By combining cooked spinach with dairy, fortified foods, or oily fish, and diversifying your greens with options like kale and bok choy, you can ensure your body effectively absorbs the minerals it needs for strong bones and overall health. For further information on bone health, consider visiting the Bone Health & Osteoporosis Foundation.
