Spinach Nutrition: The Popeye Myth and What Spinach Actually Does

Popeye ate spinach to get strong. That image stuck for almost a century. The problem is it was built on a decimal point in the wrong place.

In 1870, a German chemist named E. von Wolf published iron content data for spinach. He wrote 3.5mg of iron per 100g. A copyist later dropped the decimal, turning 3.5mg into 35mg. That error got picked up, repeated, and eventually used to position spinach as a muscle-building iron powerhouse. Hamblin T. documented this in a 1981 BMJ piece that traced the myth back to its source (Hamblin, 1981, BMJ 283:1671). The actual iron content of raw spinach is around 2.7mg per 100g. That’s not bad for a vegetable. But it’s not Popeye territory either.

Here’s the more interesting story: the nutrients spinach genuinely excels at are ones most people have never heard of.

Nutritional Profile

Per 100g raw spinach (USDA FoodData Central values):

A few of those numbers need context before they mean much. The 403% daily value for vitamin K is real. But the 15% for iron and 8% for calcium are misleading, because how much you actually absorb from spinach is well below those label numbers. That gap is what makes spinach a more complicated nutritional story than a nutrition label alone can tell. See bioavailability for how this gap works across all foods.

The Iron Story: Oxalates and Absorption

Spinach contains oxalic acid (oxalate), and it contains a lot of it — around 970mg per 100g raw. That puts it near the top of the list for common vegetables. Oxalates bind to minerals like calcium and iron in the gut, forming insoluble complexes that pass straight through without absorbing (Bos C et al., 2005, PMID 15826099).

Think of oxalate like a molecular velcro strip. It grabs onto free iron ions before your intestinal cells can take them up. The iron is physically present, but chemically locked out.

There’s also a second problem for iron specifically. Spinach iron is non-heme iron, the type found in plant foods. Non-heme iron absorbs at a rate of roughly 2 to 20%, compared to 15 to 35% for heme iron from meat. The combination of non-heme form plus oxalate binding means the iron in spinach is genuinely poor for meeting iron needs.

You can improve non-heme iron absorption by eating spinach with vitamin C. Vitamin C reduces ferric iron (Fe3+) to ferrous iron (Fe2+), which is the form your gut can actually take up. A squeeze of lemon on spinach or pairing it with bell peppers in a meal meaningfully increases what you absorb. For the full chemistry, see iron absorption science.

Cooking reduces oxalate content. Blanching spinach in boiling water for two to three minutes and discarding the water removes roughly 30 to 50% of its oxalates (Gilani GS et al., 2012, Br J Nutr, PMID 22916813). The spinach itself shrinks dramatically, which also means you end up eating more spinach by weight — and thus more iron and calcium per serving — than you would with raw leaves.

What Spinach Is Actually Great For

Vitamin K1 is where spinach genuinely stands apart. At 483mcg per 100g, it’s one of the richest dietary sources available. Vitamin K1 (phylloquinone) has two well-established roles: blood clotting and bone metabolism. Specifically, it’s required for carboxylation of proteins involved in both processes. You don’t need supplements if you eat green vegetables regularly.

The warfarin interaction is real and worth knowing. Warfarin works by blocking vitamin K-dependent clotting factors. If your vitamin K intake changes substantially week to week, your warfarin dose stops being predictable. The goal isn’t to eliminate spinach — it’s consistency. People on warfarin should work with their prescribing doctor to establish a stable weekly vitamin K intake and stay near it. Sudden large changes in spinach consumption are the problem, not spinach itself.

Folate at 194mcg per 100g (49% DV) makes spinach one of the better dietary folate sources available. Folate is required for DNA synthesis and cell division, which makes it especially important during early pregnancy for neural tube development. Raw spinach delivers more folate than cooked because folate is both water-soluble and heat-sensitive. Boiling spinach can cut folate content by more than half. If folate is your priority, eat it raw or lightly sauteed.

Lutein and zeaxanthin are fat-soluble carotenoids that concentrate in the macula of the eye. Spinach has around 12mg per 100g, making it one of the richest sources you can eat. The evidence for these compounds and age-related macular degeneration (AMD) is solid — the Age-Related Eye Disease Study 2 (AREDS2, NEI) found that lutein and zeaxanthin supplementation reduced the risk of advanced AMD progression. Dietary intake from whole foods produces similar blood concentrations.

The catch: they’re fat-soluble. Eating spinach without dietary fat produces very poor carotenoid absorption. A spinach salad with olive oil dressing absorbs meaningfully more lutein and zeaxanthin than the same salad with no dressing. This is one case where adding fat makes the food genuinely more nutritious, not less. See fat-soluble vitamins for how this class of compounds absorbs.

Nitrates are the least well-known spinach asset. Spinach is high in dietary nitrates (approximately 250mg per 100g, depending on growing conditions). These are different from the nitrites in processed meats. In the body, salivary bacteria and stomach acid convert dietary nitrates to nitric oxide, which relaxes the smooth muscle in blood vessel walls. Research has associated high dietary nitrate intake with modest reductions in blood pressure and improved exercise performance in some populations. It’s not a medication-level effect, but it’s a real physiological pathway.

Raw vs. Cooked: Which Is Better?

The honest answer is that it depends on what you want.

Raw spinach: more folate, more vitamin C, and more oxalates. Better for folate delivery. Higher oxalate burden.

Cooked spinach (blanched, sauteed, or steamed): lower oxalates, higher mineral concentration per serving because of volume reduction, and — if cooked with fat — better carotenoid delivery. Loses folate and vitamin C in proportion to heat and water contact.

Blanching is the best method for reducing oxalates without destroying all heat-sensitive nutrients. Bring water to a boil, add spinach for 90 seconds to two minutes, then drain and discard the water. The oxalates leach into the cooking water. See blanching science for how this process works chemically.

Sauteing with olive oil preserves fat-soluble compounds well and only modestly reduces folate compared to boiling. It’s probably the best all-around preparation if you’re eating spinach regularly and not targeting a specific nutrient. For a broader look at what heat does across food groups, see does cooking destroy nutrients?

The practical upshot: vary preparation. Eat some raw in salads with oil-based dressing for the carotenoids. Eat some cooked and drained to reduce oxalate load over time. Don’t count on spinach to cover your iron needs regardless of how you prepare it.