Kale vs spinach: calories compared

Most people asking are picking a green for a salad or smoothie, often for iron or fiber. Either works. Raw, they list similar iron per 3.5 oz (100 g). Kale lists about 2.6 times the fiber, nearly 4 times the calcium, and in USDA samples about 93 mg of vitamin C against 27 mg in baby spinach.

Labels overstate what you absorb. In 13 adults, only 5.1 percent of the calcium in spinach was absorbed, against 27.6 percent from milk. In a study of women, a spinach meal gave 24 percent less absorbed iron than a kale meal, a difference that did not reach significance. Added oxalate did not change absorption from kale, and the spinach was higher in calcium and polyphenols. In six volunteers, about 4.7 percent of kale's vitamin K was absorbed.

If you take warfarin, NIH advises keeping vitamin K from food steady, and green leafy vegetables are a main source. Spinach is also on published lists of foods that interact with warfarin. Plan a new daily green smoothie with whoever adjusts your dose. We hold no trial of daily raw-green smoothies and kidney stones. For adults who already form calcium stones, a 2026 review gives low-certainty support to more water, normal to high calcium, and less protein and salt.

Rotate them by taste.

Evidence behind this note

1. Level E Raw kale carries about 93 mg vitamin C per 3.5 oz (100 g) against 27 to 30 mg in spinach, while iron is similar at roughly 1 to 1.6 mg. USDA FoodData Central, Foundation Foods, release 2026-04-30
2. Level E Raw kale averages 254 mg calcium per 3.5 oz (100 g) in USDA samples, almost four times the 67 to 68 mg in baby or mature spinach. USDA FoodData Central, Foundation Foods, release 2026-04-30
3. Level B In a randomized crossover trial in 13 adults, only 5.1% of the calcium in spinach was absorbed versus 27.6% from milk at the same 200 mg calcium dose. Am J Clin Nutr, 1988
4. Level B In crossover isotope studies in 16 women, iron absorption from bread eaten with 150 g spinach was 24% lower than with 150 g kale, a difference that did not reach significance, and added oxalate did not change absorption from kale. Eur J Clin Nutr, 2008
5. Level C In 6 adults who ate 14 oz (400 g) of labeled kale with 30 g oil, about 4.7% of its vitamin K1 was absorbed, peaking in blood 6 to 10 hours later. Br J Nutr, 2010
6. Level E NIH lists green leafy vegetables, a group that includes kale, as a main food source of vitamin K and advises people on warfarin to keep vitamin K intake consistent rather than change it suddenly. NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals
7. Level C A systematic review of 149 articles on warfarin and food or supplements listed spinach among foods that call for caution in people taking warfarin. Br J Clin Pharmacol, 2021
8. Level C For people who already form calcium stones, the diet that has evidence behind it is normal calcium, less salt and less protein, and cutting oxalate is not on that list. Ann Intern Med, 2026

Written from the studies and agency guidance we hold for both foods, reviewed by the Bioma editorial system. How we verify.

Read more about these foods

• Kale and spinach: the calcium you absorb is the part that counts
• Kale: 325 percent on the label, 4.7 percent in the blood
• Spinach: the oxalate story is mostly wrong

What the studies say

• Does spinach help with weight loss? No trial has tested the vegetable itself
• Is spinach good during pregnancy? Yes as a food, but it cannot replace folic acid

Rankings and guides

• Calories: what it does and what the evidence shows
• Which foods give the most protein for the fewest calories?
• Dietary fat: what it does and how much you need
• Kale: full nutrition facts
• Spinach: full nutrition facts

More comparisons

• Spinach vs arugula

• Kale: USDA FoodData Central, Kale, raw, FDC ID 323505 · full profile · all forms of kale
• Spinach: USDA FoodData Central, Spinach, baby, FDC ID 1999632 · full profile · all forms of spinach

Each food is one USDA entry, chosen as it is usually eaten. Other cuts, brands and preparations differ; the links show them. % DV uses FDA Daily Values for adults. How we verify.