Spinach salad: the dressing decides how much you absorb

The strongest study on this page is about sport, and it found little. Across 118 randomized trials in exercising adults, nitrate-rich foods gave a trivial endurance benefit (SMD 0.15), and red spinach, a different plant from common spinach, showed no significant effect. What a spinach salad does offer can be counted. A cup without dressing, 74 g, holds about 257 mcg of vitamin K, 69 mcg of folate and 62 calories in US survey data, a recipe entry whose calories suggest toppings such as egg. How much of that reaches you depends on the fat you add. NIH notes the body absorbs only 4 to 17 percent as much vitamin K from spinach as from a tablet, and that fat eaten with the greens improves it. In a crossover trial of 12 women, absorption of carotenoids and vitamin K rose in a straight line as soybean oil dressing went from 0 to 32 g, though some women barely responded. In 16 adults, the same mixed salad with 0.99 oz (28 g) of olive oil gave 55.2 percent more carotenoid absorption than with coconut oil, over single meals.

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• A cup of spinach salad without dressing (74 g) carries about 257 ug vitamin K, 69 ug folate and 62 calories in US survey data. — US household measures, FNDDS (n = 1 food code) Evidence E source
  Per cup 74 g: vitamin K 257.4 ug, folate 68.8 ug DFE, vitamin A 174.6 ug RAE, vitamin C 14.1 mg, iron 0.9 mg, fiber 0.9 g, 62.2 calories

What your body absorbs

• NIH notes the body absorbs only 4% to 17% as much vitamin K from spinach as from a tablet, and eating fat with the greens improves absorption. — general population, NIH ODS fact sheet Evidence E source
  Phylloquinone from spinach absorbed at 4-17% of tablet level
• In a crossover RCT of 12 women, more soybean oil in salad dressing (0 to 32 g) steadily raised absorption of carotenoids and vitamin K from salad vegetables. — 12 women, 5 salads with dressings of 0, 2, 4, 8 or 32 g soybean oil (n = 12) Evidence B source
  Linear dose effect on chylomicron AUC; highest absorption of all carotenoids and fat-soluble vitamins at 32 g (P < 0.002)
• In a crossover RCT of 16 people, a salad eaten with 28 g olive oil gave 55.2% more carotenoid absorption than the same salad with coconut oil. — 16 adults, identical carotenoid-rich salad with 0.99 oz (28 g) of one of 4 fats (n = 16) Evidence B source
  Total carotenoid iAUC +55.2% olive vs coconut oil; emulsified fat +40.0% vs non-emulsified

What cooking and storage change

• By the USDA table for greens boiled in water and drained, cooking keeps only 55% of vitamin C and 60% of folate, losses a raw spinach salad avoids. — Vegetables and Vegetable Products group, greens boiled with water cover, drained (n = 1 method) Evidence E source
  Retained: vitamin C 55%, folate 60%, thiamin 80%, potassium 85%, iron 95%
• In 10 volunteers, under 2% of soluble oxalate from 100 g grilled spinach was absorbed over 24 hours, and eating it with dairy cut that further. — 10 volunteers, 100 g grilled spinach alone or with dairy or olive oil additions (n = 10) Evidence B source
  Soluble oxalate bioavailability 0.75% at 6 h and 1.93% at 24 h; lower with sour cream and high-calcium milk (P < 0.05)

What it does to your health

• In 799 French and Belgian patients with ulcerative colitis, higher salad intake was linked with clinical remission (aOR 1.73). — 2,514 IBD outpatients in 40 centers, 799 with ulcerative colitis (n = 2514) Evidence C source
  UC remission with higher salad intake aOR 1.73 (1.12 to 2.66)
• A meta-analysis of 118 RCTs found nitrate-rich foods gave only trivial endurance benefit, with beetroot helping but red spinach not. — 118 RCTs of nitrate, polyphenol and citrulline foods in exercising adults (n = 118 studies) Evidence A source
  Nitrate foods SMD 0.15 overall; no significant effect for red spinach

Safety, limits and interactions

• In stably anticoagulated healthy volunteers, 150 ug vitamin K1 a day was the threshold that lowered INR, while spinach meals gave only a short-lived response. — healthy volunteers on individualized oral anticoagulant doses for 13 weeks Evidence C source
  Threshold 150 ug/day K1 lowered INR, clinically relevant in 25%; spinach and broccoli meals short-lived response
• A 21-year review of 134 leafy greens incidents linked to California found about 2,240 confirmed US illnesses, with romaine and spinach the most common vehicles. — leafy greens incidents with a California link, 1996-2016 (n = 134 incidents) Evidence E source
  About 2,240 confirmed US cases; 298 California cases, 50 hospitalizations
• In a meta-analysis of 35 studies, spinach irrigated with wastewater averaged 2.86 mg/kg cadmium, more than 9.5 times the EU limit. — soils and crops irrigated with wastewater, 35 studies 2000-2021 (n = 35 studies) Evidence C source
  Spinach pooled mean Cd 2.86 mg/kg vs EU limit 0.2-0.3 mg/kg

What people believe that the data does not support

• In a crossover RCT of 13 adults, only 5.1% of calcium from spinach was absorbed versus 27.6% from milk. — 13 healthy adults, test meals of 200 mg labeled calcium from milk or spinach (n = 13) Evidence B source
  Calcium absorption 5.1% spinach vs 27.6% milk; within-subject difference 22.5 +/- 9.5%
• In isotope RCTs in 16 women, adding 1.26 g oxalate to a kale meal did not change iron absorption, 10.7% versus 11.5%. — 16 healthy women aged 18-45, Zurich, 13 completed both crossover studies (n = 16) Evidence B source
  Iron absorption 10.7% vs 11.5% with added oxalate (P = 0.86); spinach meal 24% lower than kale, not significant

Who this works differently for

• In a cluster RCT of 13 US elementary schools, lunch salad bars raised fruit and vegetable consumption by 84% after ten weeks. — 3,080 students in 13 Arizona elementary schools, National School Lunch Program (n = 3080) Evidence B source
  Salad bar only IRR 1.84 (95% CI 1.12 to 3.04); with marketing IRR 2.07 (1.29 to 3.31)
• One month after salad bars arrived in two Virginia schools, children chose more kinds of produce but ate 0.65 cups less fruit and vegetables. — grade 1-5 students in 2 Title I schools, 282 plates at baseline and 443 after (n = 725 plates) Evidence C source
  Consumption -0.65 cups (P < .001); types selected 1.81 to 2.58

The bottom line

Spinach calcium barely gets in. In a crossover trial of 13 adults, 5.1 percent of the calcium in spinach was absorbed against 27.6 percent from milk, in an old single-meal study. Oxalate is often blamed for blocking iron as well. In isotope trials in 16 women, adding 1.26 g of oxalate to a kale meal left iron absorption unchanged, 10.7 percent against 11.5 percent. A spinach meal in the same work absorbed 24 percent less iron than kale, a gap that did not reach significance. A raw salad keeps what boiling loses. By the USDA factor for boiled and drained greens, cooking keeps 55 percent of vitamin C and 60 percent of folate, a group figure from 1975 data never measured on spinach salad. Vitamin K matters if you take an oral anticoagulant such as warfarin. In healthy volunteers kept on anticoagulants for 13 weeks, 150 mcg of vitamin K1 a day was the dose that lowered INR, clinically relevant in a quarter of them, while spinach meals gave only a short-lived response. The threshold came from supplement doses, and a cup of the salad carries about 257 mcg, so a sudden change in how much you eat is worth raising with whoever manages your INR. Raw greens also carry food poisoning risk. A review of 134 leafy greens incidents linked to California over 21 years counted about 2,240 confirmed US illnesses, with romaine and spinach the most common vehicles. Across 35 studies, spinach irrigated with wastewater averaged 2.86 mg of cadmium per kg, over 9.5 times the EU limit, a figure that applies to regions irrigating with untreated wastewater. In 10 volunteers, under 2 percent of the soluble oxalate in 3.5 oz (100 g) of grilled frozen spinach was absorbed over 24 hours, and less with sour cream or high calcium milk. Salad bars in schools have mixed results. In 13 Arizona elementary schools, a lunch salad bar raised fruit and vegetable consumption 84 percent after ten weeks (IRR 1.84, 95 percent CI 1.12 to 3.04), measured across all produce. In two Virginia schools with no control group, children picked more kinds of produce one month after salad bars arrived and ate 0.65 cups less. Among 799 people with ulcerative colitis, those in remission ate more salad (aOR 1.73), which may simply mean people in a flare avoid raw vegetables.

Sources

1. spsl-daily-r4-01 · reference dataset
   FNDDS 75147000 (fdc 2709831) Spinach salad, no dressing, 1 cup 74 g: Vitamin K 347.9 ug/100 g, 257.4 ug · Folate DFE 93 ug/100 g, 68.8 ug · Vitamin A RAE 236 ug/100 g, 174.6 ug · Vitamin C 19.1 mg/100 g, 14.1 mg · Iron 1.22 mg/100 g, 0.9 mg · Fiber 1.2 g/100 g, 0.9 g · Energy 84 kcal/100 g, 62.2 kcal
   USDA FNDDS 2021-2023 · checked 2026-09-30
2. spsl-daily-r4-03 · agency fact sheet
   For example, the body absorbs only 4% to 17% as much phylloquinone from spinach as from a tablet [2]. Consuming vegetables at the same time as some fat improves phylloquinone absorption from the vegetables, but the amount absorbed is still lower than that from oils.
   NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-09-30
3. spsl-daily-r4-04 · RCT
   Across the entire 0-32-g range, soybean oil was linearly related to the chylomicron AUC and Cmax values for α-carotene, lycopene, phylloquinone, and retinyl palmitate...Absorption of all carotenoids and fat-soluble vitamins was highest with 32 g oil (P < 0.002).
   Am J Clin Nutr, 2017 · checked 2026-09-30
4. spsl-daily-r4-05 · RCT
   Similarly, the positive iAUC1-10h of TC, α-carotene, and lycopene were 55.2%, 110.8%, and 45.8%, respectively, higher with olive oil than with coconut oil. Emulsified fat induced 40.0% greater positive iAUC1-10h of TC than nonemulsified fat.
   Am J Clin Nutr, 2023 · checked 2026-09-30
5. spsl-daily-r4-02 · reference dataset
   USDA-RETN-R6:3005 VEG,GREENS,BOILED,WATER COVER DRAIN: vitamin_c_mg 55% · folate_total_ug 60% · thiamin_mg 80% · potassium_mg 85% · iron_mg 95%
   USDA Table of Nutrient Retention Factors, Release 6, 2007 · checked 2026-09-30
6. spsl-daily-r4-08 · RCT
   The mean bioavailability of soluble oxalate in the grilled spinach was 0.75+/-0.48% over a 6-hour period after intake and was 1.93+/-0.85% measured over a 24-hour period. Addition of sour cream and Calci-Trim milk reduced the availability of the oxalate in the spinach significantly (P<0.05) in both the 6-hour and 24-hour collection periods.
   Asia Pac J Clin Nutr, 2003 · checked 2026-09-30
7. spsl-daily-r4-14 · cross-sectional
   Among UC patients, clinical remission was associated with a higher intake of fruits (aOR 1.72 [1.15-2.56]) and salad (aOR 1.73 [1.12-2.66]).
   Dig Liver Dis, 2026 · checked 2026-09-30
8. spsl-daily-r4-15 · meta-analysis of RCTs
   Trivial but significant benefits were demonstrated for consumption of nitrate and polyphenol-rich foods (SMD=0.15 and 0.17, respectively, p<0.001)...Among nitrate-rich foods, beneficial effects were seen for beetroot, but not red spinach or Swiss chard and rhubarb.
   J Int Soc Sports Nutr, 2021 · checked 2026-09-30
9. spsl-daily-r4-09 · clinical dose-response study
   The threshold K(1) dose causing a statistically significant lowering of the INR was 150 microg/day. In 25% of the participants the INR change was regarded as clinically relevant at a vitamin K intake of 150 microg/day...The short-lived response after meals of spinach and broccoli suggested an inefficient bioavailability from these 2 sources.
   Blood, 2004 · checked 2026-09-30
10. spsl-daily-r4-10 · surveillance review
    In the 21-year period analyzed, 134 incidents were identified, the majority of which were surveillance related. Approximately 2,240 U.S. cases of confirmed illness were reported (298 California cases resulting in 50 hospitalizations). Romaine lettuce and spinach were the most commonly implicated vehicles.
    J Food Prot, 2019 · checked 2026-09-30
11. spsl-daily-r4-11 · meta-analysis of occurrence
    Certain species show extreme bioaccumulation, with Jew mallow (41.35 mg/kg), beet (23.19 mg/kg), and spinach (pooled mean 2.86 mg/kg) exceeding the EU safety limit (0.2-0.3 mg/kg) by factors of > 130, > 77, and > 9.5, respectively.
    Environ Monit Assess, 2026 · checked 2026-09-30
12. spsl-daily-r4-06 · RCT
    Absorption was higher from milk in every case, with the mean absorption from milk averaging 27.6% and from spinach, 5.1%.
    Am J Clin Nutr, 1988 · checked 2026-09-30
13. spsl-daily-r4-07 · RCT
    geometric mean iron absorption from wheat bread rolls with kale (10.7%) did not differ significantly from wheat rolls with kale plus 1.26 g OA added as potassium oxalate (11.5%, P=0.86).
    Eur J Clin Nutr, 2008 · checked 2026-09-30
14. spsl-daily-r4-12 · cluster RCT
    In contrast, after ten weeks of exposure, stand-alone school lunch salad bars significantly increased students' consumption of FV (IRR = 1.84, 95% CI 1.12, 3.04) compared to the wait-listed control.
    Int J Behav Nutr Phys Act, 2025 · checked 2026-09-30
15. spsl-daily-r4-13 · quasi-experimental
    At post, students selected more types of FVs (1.81-2.58; P < .001), although FV consumption decreased by 0.65 cups (P < .001).
    J Nutr Educ Behav, 2018 · checked 2026-09-30