Lettuce and spinach: the gap inside one leaf

The sharpest figure on this page is not about either leaf beating the other, and no study here has compared the two. In 19 healthy adults aged 22 to 31, two visually identical lettuces grown with different fertilizer carried 530 mg and 3 mg of nitrate in a 1.8 oz (50 g) portion. Only the high-nitrate one lowered systolic blood pressure, by 4.9 plus or minus 4.2 mmHg between three and six hours after eating, in a double-blind crossover. That is a 177-fold gap inside one species of lettuce, wider than anything a composition table shows between the two leaves. The caution this page carries is about oxalate, and it is narrower than it looks. A systematic review of 26 dietary intervention studies in people who form urinary stones pools nothing and names no threshold in grams. It reports only that controlling oxalate intake, along with sodium, calcium, citrate and protein, shifted blood and urine stone markers. The table does give spinach its famous win on paper. Baby spinach held 68.35 mg of calcium per 3.5 oz (100 g) against 14.24 mg in iceberg lettuce across 8 retail samples of each, although the spinach samples themselves ran from 48.2 to 92.1 mg. How much of that calcium anyone takes up is not measured anywhere on this page.

How much is actually in it

• In USDA Foundation Foods sampling, baby spinach held 68.35 mg of calcium per 3.5 oz (100 g) against 14.24 mg in iceberg lettuce, with the spinach samples spanning 48.2 to 92.1 mg. — retail samples analyzed for USDA Foundation Foods, release 2026-04-30, 8 samples of each item (n = 8 spinach and 8 lettuce samples) Evidence E source
  Calcium 68.35 mg per 3.5 oz (100 g) in baby spinach (range 48.2 to 92.1, spread 64%) against 14.24 mg in iceberg lettuce (range 10.9 to 17.2, spread 44%), spinach folate 116.5 micrograms (range 90.4 to 155, spread 55%)

What a real portion looks like

• In the USDA survey food table a cup of raw spinach weighs 0.88 oz (25 g) and a cup of raw lettuce 35 g, while the guideline salad amount is 1.8 oz (50 g) of spinach against 2.5 oz (70 g) of lettuce. — USDA FNDDS survey foods Spinach raw (code 72125100) and Lettuce raw (code 75113000) Evidence E source
  Spinach 1 cup 25 g, 1 leaf 10 g, guideline amount in salad 50 g; lettuce 1 cup 35 g, 1 leaf 8 g, 1 head 539 g, guideline amount in salad 70 g

What your body absorbs

• In a randomized isotope trial in adult men and women, manganese was absorbed at 5.20% from lettuce and 3.81% from spinach against 8.90% from manganese chloride. — adult men and women, each consuming three test meals in random order with intrinsically or extrinsically labeled 54Mn, lettuce meals 9.65 micromol Mn and other meals 22.50 micromol Mn Evidence B source
  Absorption 8.90% from MnCl2, 5.20% from lettuce, 3.81% from spinach, 2.16% from wheat and 1.71% from sunflower seeds, biological half-life unchanged by source
• By the NIH Office of Dietary Supplements, the body absorbs only 4% to 17% as much phylloquinone from spinach as from a tablet, and spinach and iceberg lettuce are among the most common vitamin K sources in the United States diet. — general population, NIH Office of Dietary Supplements vitamin K fact sheet for health professionals Evidence E source
  Phylloquinone absorption from spinach 4% to 17% of that from a tablet, about 80% for free phylloquinone

What cooking and storage change

• In field trials, a preharvest acetic acid spray made Salmonella 7.1 times less likely to be found on lettuce and changed nothing for Escherichia coli O157 on spinach. — field-grown leafy lettuce, spinach and cabbage sprayed one day before harvest with 0.3% to 0.7% acetic acid or 0.1% to 0.3% chitosan Evidence C source
  Salmonella 7.1 times more likely on untreated than on 0.7% acetic acid sprayed lettuce (95% CI 4.1 to 12.2), no difference in E. coli O157 prevalence on treated and untreated spinach or cabbage, chitosan ineffective on lettuce
• By the USDA nutrient retention table for vegetables, boiling greens in water that covers them and draining leaves 55% of vitamin C and 60% of folate. — USDA Table of Nutrient Retention Factors Release 6, group Vegetables and Vegetable Products (code 11), method code 3005, table dated Sep-75 Evidence E source
  Vitamin C 55%, folate 60%, thiamin 80%, potassium and phosphorus 85%, calcium, iron and magnesium 95%

What it does to your health

• In a double-blind crossover trial in 19 young adults, two visually identical lettuces grown under different fertilization carried 530 mg and 3 mg of nitrate per 50 g portion, and only the high-nitrate one lowered systolic blood pressure, by 4.9 mmHg. — 19 healthy participants aged 22 to 31, single 1.8 oz (50 g) portions of intact lettuce leaves, ambulatory blood pressure over 6 hours (n = 19) Evidence B source
  Systolic BP 4.9 plus or minus 4.2 mmHg lower between 3 and 6 hours after the high-nitrate lettuce, plasma nitrate up 240% and salivary nitrate up 910%

Safety, limits and interactions

• A systematic review of 26 intervention studies in people with urinary stones found that controlling oxalate intake is one of the dietary strategies that changed serum and urinary stone markers. — people with urolithiasis in 26 intervention studies published up to July 2025 (n = 26 studies) Evidence C source
  Significant changes in serum and urinary parameters related to urolithiasis from controlling sodium, oxalate, calcium, citrate and protein intake and from low-calorie diets
• In a market survey of Alberta produce, 27.1% of spinach samples carried Escherichia coli against 8.2% across all sampled produce, and the single Cryptosporidium finding was also in spinach. — 673 produce samples from 36 farmers and public markets in Alberta between 21 June and 7 October 2007, including 128 lettuce and 59 spinach samples (n = 59 spinach and 128 lettuce samples) Evidence C source
  E. coli in 8.2% of samples overall, from 4.4% for carrots to 27.1% for spinach, no Salmonella, E. coli O157:H7 or Campylobacter in any sample, Cryptosporidium in one spinach sample (0.6%)

What people believe that the data does not support

• A modeling study of Belgian adults eating carrots, tomatoes, lettuce, spinach and potatoes found insufficient evidence to recommend organic over conventional vegetables. — a representative sample of 3245 Belgian adults and 522 Flemish organic and conventional consumers, probabilistic intake simulation (n = 3767) Evidence C source
  Nutrient and contaminant intakes higher or lower for organic depending on the component and the vegetable, with the higher total vegetable intake of organic consumers outweighing concentration differences
• The EU register records the claim that a combination of red and green spinach with chicory and chard protects blood lipids from oxidative damage as non-authorized, and no claim about spinach or lettuce is authorized. — EU Register on nutrition and health claims, snapshot 2026-09-21, six claims filed under spinach and none authorized, no claim filed under lettuce at all Evidence E source
  Status Non-authorized

Who this works differently for

• By the NIH Office of Dietary Supplements, people taking warfarin and similar anticoagulants need a consistent vitamin K intake because sudden changes can increase or decrease the drug effect. — people taking warfarin, phenprocoumon, acenocoumarol or tioclomarol Evidence E source
  Sudden changes in vitamin K intake increase or decrease the anticoagulant effect

What is still unknown

• Laboratory and animal data suggest probiotics may cut renal calcium oxalate deposition in rat models of hyperoxaluria while leaving urinary oxalate unchanged. — 27 in vivo studies in chickens, mice and rats published between 2005 and 2025 under antinutrient-rich diets (n = 27 studies) Evidence D source
  Renal calcium oxalate deposition SMD 0.77 in rat hyperoxaluria models, urinary oxalate SMD 0.20 and not significant, hepatic iron SMD 2.05 in broilers
• A systematic review of 23 studies in 305 healthy people put endogenous oxalate production at 23.8 mg a day, with ascorbic acid turnover accounting for up to 40 to 60 percent of it. — 305 healthy subjects across 7 of 23 eligible studies reporting total endogenous oxalate production, searched December 2025 (n = 305) Evidence C source
  Endogenous oxalate 23.8 mg a day (95% CI 23 to 24.6, range 17 to 34), ascorbic acid up to 40 to 60 percent, hydroxyproline about 15 percent, glycine under 10 percent

The bottom line

Absorption is where the composition table loses some of its authority. In a randomized isotope study, manganese was absorbed at 5.20 percent from lettuce and 3.81 percent from spinach, against 8.90 percent from manganese chloride. That work dates from 1991, its abstract does not say how many people took part, and the lettuce meals carried a lower manganese dose than the others. Vitamin K behaves the same way. The NIH Office of Dietary Supplements says the body absorbs only 4 to 17 percent as much phylloquinone from spinach as from a tablet. The same fact sheet names spinach and iceberg lettuce among the most common vitamin K sources in the United States diet. Measure by weight rather than by cup. A cup of raw spinach weighs 0.88 oz (25 g) and a cup of raw lettuce 35 g in the USDA survey table, and the guideline salad amount is 1.8 oz (50 g) of spinach against 2.5 oz (70 g) of lettuce. Cooking separates the two in practice. The USDA retention factor for boiled greens leaves 55 percent of vitamin C and 60 percent of folate, and it is set for the whole greens group rather than for either leaf by name. Spinach gets boiled and lettuce almost never does, so that loss lands on one half of the pair. For caution, the oxalate review above pools nothing, is not built from randomized trials and names no threshold in grams, so it does not turn into a rule about eating less spinach. The second caution card is microbiological. In a 2007 market survey in one Canadian province, 27.1 percent of 59 spinach samples carried Escherichia coli against 8.2 percent of all produce sampled, and the single Cryptosporidium finding was in spinach. No Salmonella, E. coli O157:H7 or Campylobacter turned up in any sample, and E. coli there is an indicator of fecal contamination rather than a pathogen. Field work points the same way. A preharvest acetic acid spray made Salmonella 7.1 times less likely to be found on lettuce and did nothing for E. coli O157 on spinach. If you take warfarin or a similar anticoagulant, this pair matters more to you than to anyone else. The NIH fact sheet says the point is consistency, because sudden changes in vitamin K intake raise or lower the drug effect, and it gives no microgram threshold. Swapping a spinach salad for a lettuce one week after week is the kind of change it means. Two things this page cannot answer. Our reference layers carry no oxalate figure for either leaf, so the argument everyone has about spinach and stones has no number attached, against a background of 23.8 mg of oxalate a day that the body makes on its own. And no study has compared lettuce with spinach on any clinical outcome. The only work pointing at a fix is in animals, where probiotics cut renal calcium oxalate deposition in rat models of hyperoxaluria while leaving urinary oxalate unchanged. The organic question is unsettled too. A Belgian modeling study covering 3767 adults found insufficient evidence to prefer organic vegetables, with how much people ate outweighing how it was grown. Labels stay quiet by law, with six health claims filed in the EU under spinach, none authorized, and none filed under lettuce at all.

Sources

1. letsp-daily-r5-12 · reference dataset
   Spinach, baby | Calcium, Ca | 68.35 MG | range 48.2-92.1, median 70.4, 8 samples, spread 64% || Lettuce, iceberg, raw | Calcium, Ca | 14.24 MG | range 10.9-17.2, median 14.55, 8 samples, spread 44%
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-09-25
2. letsp-daily-r5-13 · reference dataset
   Spinach, raw | FNDDS 72125100 | fdc_id 2709614 | 1 cup = 25 g | 1 leaf = 10 g | Guideline amount in salad = 50 g || Lettuce, raw | FNDDS 75113000 | fdc_id 2709789 | 1 cup = 35 g | 1 leaf = 8 g | 1 head = 539 g | Guideline amount in salad = 70 g
   USDA FNDDS, Spinach raw code 72125100 and Lettuce raw code 75113000 · checked 2026-09-25
3. letsp-daily-r5-02 · randomized controlled trial
   Absorption of 54Mn from MnCl2 (8.90%) was greater than from lettuce (5.20%), spinach (3.81%), wheat (2.16%) or sunflower seeds (1.71%), but the biological half-life did not vary with the source of Mn.
   J Nutr, 1991 · checked 2026-09-25
4. letsp-daily-r5-07 · agency fact sheet
   The most common sources of vitamin K in the U.S. diet are spinach; broccoli; iceberg lettuce; and fats and oils, particularly soybean and canola oil [5,7]. ... For example, the body absorbs only 4% to 17% as much phylloquinone from spinach as from a tablet [2].
   NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-09-25
5. letsp-daily-r5-05 · field intervention trials
   No significant differences in E. coli O157 prevalence were found for untreated and treated cabbage heads and spinach plants (P > 0.05). ... Salmonella was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; P < 0.0001).
   J Food Prot, 2019 · checked 2026-09-25
6. letsp-daily-r5-14 · reference dataset
   VEG,GREENS,BOILED,WATER COVER DRAIN | Vegetables and Vegetable Products (11) | Retn_Code 3005 | vitamin_c_mg 55% | folate_total_ug 60% | thiamin_mg 80% | potassium_mg 85%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, code USDA-RETN-R6:3005 · checked 2026-09-25
7. letsp-daily-r5-01 · randomized controlled crossover trial
   In a randomised cross-over design, 19 healthy participants (22-31 years) received 50 g of lettuce containing either 530 mg (8.4 mmol) nitrate + 11 mg (0.03 mmol) phenolic compounds (HNLP); or 3 mg nitrate (0.05 mmol) + 77 mg (0.2 mmol) phenolic compounds (LNHP), obtained by differential fertilisation. ... Systolic BP was reduced 4.9 ± 4.2 mmHg (P = 0.031) between 3 and 6 h after ingestion of HNLP compared with LNHP; systolic BP differences were negatively correlated (P = 0.004) with differences in saliva nitrate concentrations.
   Eur J Nutr, 2022 · checked 2026-09-25
8. letsp-daily-r5-03 · systematic review
   A total of twenty-six articles were included, focusing on dietary interventions such as controlling sodium, oxalate, calcium, citrate and protein intake, as well as low-calorie diets.
   Nutr Res Rev, 2025 · checked 2026-09-25
9. letsp-daily-r5-04 · microbiological prevalence survey
   E. coli was isolated from 8.2% of the samples that included lettuce, spinach, carrots, and green onions. ... The percentage of positive samples ranged from 4.4% for carrots to 27.1% for spinach. Salmonella, E. coli O157:H7, and Campylobacter spp. were not isolated from any of the samples. Cryptosporidium was identified by PCR in one sample of spinach (0.6% of the samples).
   J Food Prot, 2009 · checked 2026-09-25
10. letsp-daily-r5-06 · dietary intake modeling study
    In public health terms, there is insufficient evidence to recommend organic over conventional vegetables. The general higher vegetable consumption of organic compared to conventional consumers outweighs usually the role of differences in nutrient and contaminant concentrations between organic and conventional vegetables.
    Food Chem Toxicol, 2010 · checked 2026-09-25
11. letsp-daily-r5-11 · regulatory register entry
    POL-HC-8442 A combination of red spinach, green spinach, red chicory, green chicory, green leaf chard, red leaf chard, red Swiss chard, golden Swiss chard and white Swiss chard Contributes to the protection of blood lipids from oxidative damage -/- Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-8442, snapshot 2026-09-21 · checked 2026-09-25
12. letsp-daily-r5-08 · agency fact sheet
    People taking warfarin and similar anticoagulants need to maintain a consistent intake of vitamin K from food and supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect [45].
    NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-09-25
13. letsp-daily-r5-09 · systematic review and meta-analysis of in vivo animal studies
    In rat models of hyperoxaluria, probiotics reduced renal calcium oxalate deposition (SMD = 0.77; p = 0.0001), though the impact on urinary oxalate levels was not significant (SMD = 0.20).
    Compr Rev Food Sci Food Saf, 2026 · checked 2026-09-25
14. letsp-daily-r5-10 · systematic review
    Weighted mean of endogenous oxalate production was 23.8 mg/day (95% CI 23-24.6 mg/day) with a range of 17-34 mg/day. Daily turnover from the metabolic pool of ascorbic acid may account for up to 40% - 60% of total endogenous oxalate production.
    Urolithiasis, 2026 · checked 2026-09-25