What's Better for Iron: Kale or Spinach?

November 12, 2025 •

4 min read

According to the National Institutes of Health, a 100-gram serving of cooked spinach contains more iron than the same amount of cooked kale. However, the crucial question when comparing what's better for iron, kale or spinach, lies not in the total quantity but in the body's ability to actually absorb the mineral.

Quick Summary

This guide compares kale and spinach to determine which is superior for iron intake. It explains the concept of bioavailability, detailing why spinach's high oxalate content limits iron absorption and how kale offers a more accessible source of non-heme iron.

Key Points

Spinach has more iron, but kale has better bioavailability: Spinach contains more iron by volume, but its high oxalate content significantly inhibits absorption, making kale a more efficient source of usable iron for the body.
Iron absorption depends on preparation: Pairing leafy greens with vitamin C-rich foods and cooking them can dramatically increase the amount of non-heme iron your body can absorb.
Oxalates are the main inhibitor in spinach: High levels of oxalic acid in spinach bind with iron, preventing its absorption in the digestive tract.
Kale is a better source of vitamin C: The higher vitamin C content in kale naturally aids in iron absorption, giving it a built-in advantage.
Cooking reduces oxalates in spinach: Boiling spinach can reduce its oxalate content, improving the absorption of both iron and calcium.
A varied diet is the best approach: Instead of choosing one over the other, incorporating both kale and spinach into your diet ensures a broader range of vitamins, minerals, and overall health benefits.

Kale vs. Spinach: The Iron Content Myth

For years, spinach has been championed as an iron powerhouse, largely thanks to a popular but mistaken belief fueled by Popeye the Sailor. While it's true that spinach contains a notable amount of non-heme iron, its effectiveness is hampered by the presence of oxalic acid. In contrast, kale contains lower overall iron but significantly less oxalic acid, allowing the body to absorb a higher percentage of the iron present. Understanding this nuance is key for anyone seeking to maximize their plant-based iron intake.

The Challenge of Iron Bioavailability

Iron from plant sources (non-heme iron) is less readily absorbed by the human body compared to the heme iron found in meat, poultry, and fish. The absorption rate of non-heme iron can be drastically influenced by other compounds found in food. In the case of spinach, high levels of oxalates bind to iron in the digestive system, creating a compound that the body cannot easily absorb. A study cited on ResearchGate found that iron absorption from a meal with spinach was lower than a meal with kale, highlighting the impact of these absorption inhibitors. This is why adding spinach alone to your diet, without a vitamin C source, may not boost your iron levels as effectively as you might think.

How to Maximize Iron Absorption from Leafy Greens

Fortunately, there are several ways to improve the absorption of non-heme iron from both kale and spinach:

Pair with Vitamin C: Consuming greens with a source of vitamin C, such as citrus fruits, bell peppers, or tomatoes, can significantly increase the absorption of non-heme iron. Vitamin C helps convert iron into a more easily absorbable form.
Cook Your Greens: Cooking, especially boiling, can help reduce the levels of oxalates in spinach, thereby improving the bioavailability of both its iron and calcium. Lightly steaming or sautéing can also help break down cell walls, making nutrients more accessible.
Use a Cast-Iron Skillet: Cooking your food in a cast-iron skillet can actually transfer some of the iron from the pan to your meal, providing an extra boost of the mineral.
Time Your Meals: Avoid consuming calcium-rich foods like dairy products, or beverages like coffee and tea, at the same time as your iron-rich greens. These items can inhibit iron absorption.

Nutritional Comparison: Kale vs. Spinach

Beyond iron, these greens offer different nutritional profiles. A side-by-side comparison reveals the full picture.


Feature	Spinach	Kale
Iron Content	Higher by quantity	Lower by quantity
Iron Bioavailability	Limited by high oxalates	Superior due to low oxalates
Oxalate Content	Very high	Low
Vitamin C Content	Lower	Higher
Calcium Content	Lower	Higher
Vitamin K Content	Very high	High
Fiber Content	Lower	Higher
Texture	Softer, milder flavor	Heartier, chewier texture

The Final Verdict: Choosing the Right Green for Your Needs

Ultimately, deciding what's better for iron between kale and spinach depends on your overall dietary approach. If you are specifically focused on improving iron absorption from plant-based sources, kale might be the more efficient choice due to its lower oxalate content. However, spinach's higher iron quantity can still contribute significantly when prepared correctly with absorption enhancers like vitamin C. For example, a spinach salad with citrus dressing provides both the iron and the vitamin C needed for better absorption. Conversely, kale is already rich in vitamin C, giving it a natural advantage in this regard. Both vegetables are exceptionally healthy, packed with a wide range of other vitamins, minerals, and antioxidants. The best strategy is not to pick a single winner but to incorporate a variety of leafy greens into your diet to reap the unique benefits of each. Whether you prefer the softer texture of spinach in a smoothie or the heartier chew of kale in a salad, both deserve a place on your plate.

For more detailed nutritional information on these greens, consult reliable resources like the National Institutes of Health.

Conclusion

While spinach contains a higher absolute amount of iron, its bioavailability is significantly reduced by its high oxalate content. Kale, with lower oxalate levels, offers superior iron absorption despite having a lower total iron quantity. By pairing either green with a source of vitamin C and employing proper cooking techniques, you can effectively enhance the body's ability to utilize the iron they contain. The final choice between kale and spinach is not a matter of one being definitively 'better' but depends on your nutritional goals and preparation methods. A varied diet that includes both is the most comprehensive approach to a healthy lifestyle.

Frequently Asked Questions

Yes, cooking both kale and spinach, especially boiling spinach, can increase iron absorption. Cooking helps break down cell walls and reduce the inhibitory effects of compounds like oxalates in spinach, making the iron more bioavailable.

By raw weight, spinach contains a higher amount of iron than kale. However, this measurement does not account for bioavailability, the rate at which the body can actually absorb the mineral.

You can improve iron absorption by pairing leafy greens with vitamin C-rich foods like citrus fruits or bell peppers. Additionally, cooking the greens and avoiding consumption with calcium-rich foods, coffee, or tea can help.

No, the iron in spinach is not useless, but its absorption is limited due to high oxalate levels. A small portion of the iron is still absorbed, and proper preparation can increase that amount.

No, many other plant-based foods contain iron, including legumes, fortified cereals, and seeds. Both kale and spinach are considered valuable, but not exclusive, sources of non-heme iron.

Kale does contain oxalates, but at significantly lower levels than spinach. This is why the iron in kale is more readily absorbed by the body.

Non-heme iron is the form of iron found in plant-based foods, as opposed to heme iron, which is found in animal products. Non-heme iron is less easily absorbed by the body.