Why Kale Is Better For You - Short 2/8/2026
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Why Kale Is Better For You - Short 2/8/2026
Kale's low water content is the reason it outperforms other leafy greens in nutrient density — gram for gram, it delivers dramatically more vitamins and fiber than iceberg lettuce.
Script
You have probably heard that kale is better for you, but why is this?
For comparison, iceberg is made of 96% water by weight while kale is at 84%.
This makes it one of the highest in fiber, Vitamin C, and Vitamin K of any leafy green. Gram for gram, kale has over 15 times more Vitamin K and over 30 times more Vitamin C than iceberg lettuce.
So, what is stopping you from eating more kale?
Sources
Kale Is 84% Water by Weight
U.S. Department of Agriculture, Agricultural Research Service. "Kale, raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/168421/nutrients
USDA standard reference data lists raw kale at 84.04g of water per 100g serving, meaning kale is approximately 84% water by weight.
"Kale." Wikipedia, citing USDA nutrient data.
https://en.wikipedia.org/wiki/Kale
States that raw kale is 84% water, 9% carbohydrates, 4% protein, and 1% fat per USDA data.
Iceberg Lettuce Is 96% Water by Weight
U.S. Department of Agriculture, Agricultural Research Service. "Lettuce, iceberg (includes crisphead types), raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/169248/nutrients
USDA standard reference data lists raw iceberg lettuce at approximately 95.6g of water per 100g serving, commonly rounded to 96% water by weight.
MyFoodData. "Nutrition Facts for Iceberg Lettuce." Based on USDA Food Data Central Standard Release.
https://tools.myfooddata.com/nutrition-facts/169248/wt1
Confirms iceberg lettuce is 96% water by weight.
Kale Is One of the Highest in Fiber Among Leafy Greens
U.S. Department of Agriculture, Agricultural Research Service. "Kale, raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/168421/nutrients
Raw kale contains 3.6g of dietary fiber per 100g. For comparison, spinach has 2.2g and iceberg lettuce has approximately 1.2g per 100g.
SouperSage. "Nutrition Comparison: Kale Vs Spinach." Using 2020 USDA and NIH data.
https://www.soupersage.com/compare-nutrition/kale-vs-spinach
Kale has 86% more dietary fiber than spinach — kale has 4.1g of dietary fiber per 100 grams and spinach has 2.2g of dietary fiber. (Note: slight variation in fiber values between USDA entries is common depending on the specific dataset referenced.)
FoodStruct. "Lettuce vs. Kale raw — Health Impact and Nutrition Comparison."
https://foodstruct.com/compare/lettuce-vs-kale-nutrition
Kale provides nearly three times more fiber than lettuce. Kale is usually higher in insoluble fiber, while lettuce contains more soluble fiber.
Kale Has Over 30 Times More Vitamin C Than Iceberg Lettuce
U.S. Department of Agriculture, Agricultural Research Service. "Kale, raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/168421/nutrients
Raw kale contains 93.4mg of Vitamin C per 100g.
U.S. Department of Agriculture, Agricultural Research Service. "Lettuce, iceberg (includes crisphead types), raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/169248/nutrients
Raw iceberg lettuce contains approximately 2.8mg of Vitamin C per 100g.
SouperSage. "Nutrition Comparison: Kale Vs Spinach." Using 2020 USDA and NIH data.
https://www.soupersage.com/compare-nutrition/kale-vs-spinach
Kale has 232% more Vitamin C than spinach — kale has 93.4mg per 100 grams and spinach has 28.1mg. This further supports kale's standing as one of the highest Vitamin C leafy greens.
Kale Has Over 15 Times More Vitamin K Than Iceberg Lettuce
U.S. Department of Agriculture, Agricultural Research Service. "Kale, raw." FoodData Central, SR Legacy.
https://fdc.nal.usda.gov/food-details/168421/nutrients
Raw kale contains 389.6µg of Vitamin K per 100g in the SR Legacy dataset. Other USDA-sourced references report values as high as 704.8µg per 100g depending on the dataset and kale variety.
Nutrition-and-You.com. "Kale Nutrition facts and Health benefits." Citing USDA National Nutrient Database.
https://www.nutrition-and-you.com/kale.html
Lists kale Vitamin K content at 704.8µg per 100g. Notes that because of its high vitamin-K content, patients taking anti-coagulants such as warfarin are encouraged to avoid kale.
Strongr Fastr. "Iceberg lettuce: FAQ, Nutrition Facts, & Macros." Source: USDA Nutrient Database.
https://www.strongrfastr.com/foods/iceberg-lettuce-11252
Iceberg lettuce contains around 24 micrograms of Vitamin K per 100 grams.
Kale Is More Nutrient Dense Than Iceberg Lettuce Overall
di Noia, J. "Defining Powerhouse Fruits and Vegetables: A Nutrient Density Approach." Preventing Chronic Disease (CDC), 11:E95, 2014.
https://www.cdc.gov/pcd/issues/2014/13_0390.htm
This CDC-published study ranked 47 fruits and vegetables by nutrient density. Kale scored 49.07 out of 100. Iceberg lettuce did not meet the threshold to qualify as a "powerhouse" vegetable in this ranking.
Harvard Health Publishing. "Salad greens: Getting the most bang for the bite." Harvard Medical School, 2021.
https://www.health.harvard.edu/staying-healthy/salad-greens-getting-the-most-bang-for-the-bite
Lists spinach, kale, romaine, watercress, and arugula among the most nutritious greens. Notes that some greens like iceberg lettuce are not nutrient powerhouses by comparison.
Summary Table
| Nutrient (per 100g raw) | Kale | Iceberg Lettuce | Kale Advantage |
|---|---|---|---|
| Water | 84% | 96% | 12% less water = more room for nutrients |
| Dietary Fiber | 3.6g | 1.2g | ~3x more |
| Vitamin C | 93.4mg | 2.8mg | ~33x more |
| Vitamin K | 389.6 – 704.8µg | 24.1µg | ~16–29x more |
| Calories | 35–49 kcal | 14 kcal | Higher due to actual nutrient content |
All values sourced from USDA FoodData Central, SR Legacy dataset.