Cabbage or lettuce: vitamin C on one side, vitamin K on the other

The one trial that fed ordinary lettuce at a meal is small. In 16 healthy men aged 20 to 30, adding 3.5 oz (100 g) of romaine lettuce to one high-fat meal lowered the 4-hour glucose curve to 361.9 from 385.7 mg/dL, a single meal in a single kind of person. Most of what separates the two is composition. Raw red cabbage averages 54 mg of vitamin C per 3.5 oz (100 g) and green cabbage 40 mg, against 15 mg in green leaf lettuce and 4.6 mg in romaine in USDA samples, which hold no iceberg figure. Lettuce leads on vitamin K1, with wide spread between samples: green leaf lettuce carries about 119 mcg per 3.5 oz (100 g), romaine 102, green cabbage 59 and iceberg 20. A cup of raw cabbage, 90 g, gives about 28 calories, and a cup of lettuce, 35 g, about 7, both recalculated from 100 g values.

How much is actually in it

• Raw green cabbage averages 40 mg vitamin C per 3.5 oz (100 g) and red cabbage 54 mg, against 5 to 15 mg in romaine and leaf lettuces. — USDA Foundation Foods samples, raw (n = 8-14 per food) Evidence E source
  Vitamin C per 3.5 oz (100 g): red cabbage 53.88 (45.4-71.4), green cabbage 40.34 (34.8-56.3), green leaf lettuce 15.15 (11.3-20.0), red leaf 9.343 (4.33-16.3), cos/romaine 4.6 (0.8-9.3) mg
• Green leaf and romaine lettuce carry more vitamin K1 than green cabbage, about 102 to 119 vs 59 ug per 3.5 oz (100 g), while iceberg has 20 ug. — USDA Foundation Foods samples, raw (n = 8 per food) Evidence E source
  Phylloquinone per 3.5 oz (100 g): green leaf lettuce 118.5 (90.6-133.8), cos/romaine 102.0 (69.7-129.0), red leaf 73.2, green cabbage 59.4 (41.6-82.9), red cabbage 32.3, iceberg 20.5 (12.3-27.8) ug
• Potassium differs more within lettuces than between the pair: iceberg has 139 mg per 3.5 oz (100 g), red leaf lettuce 321 mg, green cabbage 207 mg. — USDA Foundation Foods samples, raw (n = 7-8 per food) Evidence E source
  Potassium per 3.5 oz (100 g): iceberg 139.3 (106-175), red leaf 321.4 (268-383), romaine 253.0, green cabbage 207.1 (184-267), red cabbage 269.1 (236-320) mg
• NIH ODS lists iceberg lettuce among the most common sources of vitamin K in the US diet. — US diet Evidence E source
  Iceberg lettuce named with spinach, broccoli and soybean/canola oil

What a real portion looks like

• US survey coding sets a cup of raw green cabbage at 90 g and 28 calories, and a cup of raw lettuce at 35 g and 7 calories. — Cabbage, green, raw (FNDDS 75103000) and Lettuce, raw (FNDDS 75113000) Evidence E source
  Per 100 g: cabbage 31 calories, lettuce 20 calories; 1 cup: 27.9 vs 7.0 calories; salad guideline amount of lettuce 70 g

What cooking and storage change

• Boiling vegetables in water to cover and draining keeps about 75% of vitamin C and 65% of folate by the USDA retention table for the vegetable group. — Vegetables and Vegetable Products group, other vegetables, boiled, water to cover, drained (USDA R6 code 3775) Evidence E source
  Retained: folate 65%, vitamin C 75%, thiamin 80%, potassium 90%

What it does to your health

• In a crossover RCT on 16 young men, adding 100 g romaine lettuce to a high-fat meal lowered the 4-hour glucose curve to 361.9 from 385.7 mg/dL and lowered insulin. — Healthy men aged 20-30, BMI about 23.7, one test meal per arm (n = 16) Evidence B source
  Glucose AUC 361.9 vs 385.7 (control) mg/dL, P < 0.05; peak insulin 33.5 vs 43.8 uIU/mL; lipids and cytokines unchanged
• In a 4-week RCT on 48 adults, 100 g a day of lettuce grown with a seaweed biostimulant raised serum iron by about 38%, an effect not tested for ordinary lettuce. — Healthy adults of both sexes, 100 g lettuce daily or 30 mg iron tablet, 4 weeks (n = 48) Evidence B source
  Serum iron about +38%, transferrin saturation about +47%, total cholesterol about -19% with biostimulated lettuce
• A meta-analysis of 89 observational studies linked high cruciferous vegetable intake with 19% lower risk of gastrointestinal cancers, and broccoli plus cabbage with 36% lower gastric cancer risk. — 81 articles, 89 observational studies Evidence C source
  All GI cancers RR 0.81 (0.76-0.87); broccoli and cabbage, gastric cancer RR 0.64 (0.47-0.87)
• A meta-analysis of 22 case-control and cohort studies linked cruciferous vegetables with 19% lower gastric cancer risk, with a similar result for cabbage alone. — 16 case-control and 6 prospective studies Evidence C source
  RR 0.81 (0.75-0.88); prospective studies borderline

Safety, limits and interactions

• A meta-analysis of 23 dietary intervention trials found cruciferous vegetables, including cabbage, raised CYP1A2 drug-metabolizing activity by 20-40%. — Human dietary intervention trials with broccoli, Brussels sprouts, cabbage, cauliflower, radish, watercress Evidence C source
  CYP1A2 activity +20-40%; GST-alpha +15-35%
• A meta-analysis of 29 Ethiopian market studies found parasites on 61% of lettuce and 53% of cabbage samples. — 6659 vegetables and fruits from farms and markets in Ethiopia (n = 6659) Evidence C source
  Parasite contamination: lettuce 61.0%, cabbage 52.9%; bacterial: lettuce 26.0%, cabbage 20.0%
• A global review of 391,291 vegetable samples found 3.85% carried parasites, and lettuce made up the largest share of the contaminated samples. — 117 studies, 2001-2021, worldwide (n = 391291) Evidence C source
  3.85% contaminated; lettuce 20.43% of positives
• A meta-analysis of 27 studies found norovirus in 7% of vegetable samples worldwide, with lettuce the most sampled vegetable. — 27 studies of vegetables worldwide Evidence C source
  Pooled prevalence 7% (3-13); farms 18%, retail 4%

What people believe that the data does not support

• The EU refused a claim that cabbage-family vegetables are particularly rich in compounds that protect cells and DNA or help eliminate toxins. — EU Register on nutrition and health claims Evidence E source
  Claim status non-authorized

Who this works differently for

• A 1984 case report described a woman on warfarin who had a heart attack five weeks after starting a weight-loss diet of lettuce, broccoli and turnip greens. — One woman aged 35 with a prosthetic aortic valve on warfarin (n = 1) Evidence D source
  Warfarin resistance attributed to dietary vitamin K
• In 225 Japanese patients with chronic kidney disease, the highest intake of other vegetables, including cabbage, went with 72% lower odds of metabolic acidosis. — Non-dialysis CKD patients in Tokyo, median age 72 (n = 225) Evidence C source
  Adjusted OR 0.28 (0.10-0.79) highest vs lowest intake

The bottom line

Potassium differs more within lettuces than between the pair. Raw iceberg has 139 mg per 3.5 oz (100 g), red leaf lettuce 321 mg, green cabbage 207 mg and red cabbage 269 mg. Boiling vegetables in water to cover and draining keeps about 75% of vitamin C and 65% of folate by the USDA retention table, a 1975 group factor never measured on cabbage itself. Lettuce is rarely cooked. The cancer link for cabbage is observational. A meta-analysis of 89 observational studies, mostly case-control, linked high cruciferous vegetable intake with 19% lower risk of gastrointestinal cancers (RR 0.81, 95% CI 0.76 to 0.87). High intake of broccoli and cabbage, counted together, went with 36% lower gastric cancer risk (RR 0.64, 0.47 to 0.87). An older meta-analysis of 22 studies found 19% lower gastric cancer risk with cruciferous vegetables (RR 0.81, 0.75 to 0.88) and a similar result for cabbage alone, but 16 of those studies were case-control and the 6 prospective ones were borderline. We found no trial of cabbage or lettuce on cancer or any other hard outcome. A lettuce and iron trial is easy to misread. In 48 healthy adults, 100 g a day for 4 weeks of lettuce grown with a seaweed biostimulant, which carried 63% more iron, raised serum iron by about 38%, and ordinary lettuce was not tested. In 225 Japanese adults with chronic kidney disease not on dialysis, the highest intake of a vegetable group that put cabbage with radishes and onions went with 72% lower odds of metabolic acidosis (OR 0.28, 0.10 to 0.79), a cross-sectional finding in odds. The EU has refused a claim that cabbage-family vegetables are particularly rich in compounds that protect cells and DNA or help clear toxins. For people on warfarin, vitamin K is the point. The NIH lists iceberg lettuce among the commonest vitamin K sources in the US diet, a ranking driven by how much of it people eat. A 1984 case report describes a 35-year-old woman with a prosthetic heart valve on warfarin who had a heart attack five weeks after starting a weight-loss diet of lettuce, broccoli and turnip greens, a single case. In dietary intervention trials, not all randomized, cruciferous vegetables including cabbage raised the activity of the drug-metabolizing enzyme CYP1A2 by 20 to 40%, with unclear clinical meaning. Contamination is the other caution. In Ethiopian markets, parasites were found on 61% of lettuce and 53% of cabbage samples, figures that do not transfer to washed retail produce. Worldwide, 3.85% of 391,291 vegetable samples carried parasites, and lettuce made up 20% of the positive ones, which is a share of positives and says nothing about how often lettuce itself is contaminated. Norovirus turned up in 7% of vegetable samples (95% CI 3 to 13), 18% on farms and 4% at retail, with lettuce the most sampled vegetable.

Sources

1. cxl-r3-01 · reference dataset
   Cabbage, red, raw: Vitamin C 53.88 MG (45.4-71.4, 8 samples); Cabbage, green, raw: 40.34 MG (34.8-56.3, 8); Lettuce, leaf, green, raw: 15.15 MG (11.3-20.0, 8); Lettuce, leaf, red, raw: 9.343 MG (4.33-16.3, 8); Lettuce, cos or romaine, raw: 4.6 MG (0.8-9.3, 14)
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
2. cxl-r3-02 · reference dataset
   Lettuce, leaf, green, raw: Vitamin K (phylloquinone) 118.5 UG (90.6-133.8, 8 samples); Lettuce, cos or romaine, raw: 102.0 UG (69.7-129.0, 8); Lettuce, leaf, red, raw: 73.2 UG (55.8-94.8, 8); Cabbage, green, raw: 59.4 UG (41.6-82.9, 8); Cabbage, red, raw: 32.3 UG (15.3-58.1, 8); Lettuce, iceberg, raw: 20.5 UG (12.3-27.8, 8)
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
3. cxl-r3-03 · reference dataset
   Lettuce, iceberg, raw: Potassium, K 139.3 MG (106.0-175.0, 8 samples); Lettuce, leaf, red, raw: 321.4 MG (268.0-383.0, 8); Lettuce, cos or romaine, raw: 253.0 MG (234.0-273.0, 7); Cabbage, green, raw: 207.1 MG (184.0-267.0, 8); Cabbage, red, raw: 269.1 MG (236.0-320.0, 8)
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
4. cxl-r3-12 · 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].
   NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-10-02
5. cxl-r3-05 · reference dataset
   Cabbage, green, raw (fdc_id 2709773): Energy 31 KCAL per 100 g; 1 cup 90 g 27.9 KCAL; Lettuce, raw (fdc_id 2709789): Energy 20 KCAL per 100 g; 1 cup 35 g 7.0 KCAL
   USDA FNDDS, FoodData Central survey foods, fdc_id 2709773 and 2709789 · checked 2026-10-02
6. cxl-r3-04 · reference dataset
   USDA-RETN-R6:3775 VEG,OTHER,BLD,WATER COVER,DRAINED - folate_total_ug 65% - vitamin_c_mg 75% - thiamin_mg 80% - potassium_mg 90%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), code 3775 · checked 2026-10-02
7. cxl-r3-06 · RCT
   The 0-4-h AUCs for glucose (385.7, 361.9, and 382.3 mg/dL for the control, lettuce, and watercress meals, respectively) were calculated to be lower when meal was consumed with lettuce compared to the control (P < 0.05) and watercress (P < 0.01) meals.
   Lipids Health Dis, 2021 · checked 2026-10-02
8. cxl-r3-07 · RCT
   The consumption of lettuce with SwE application increased serum iron by about 38%, transferrin saturation by about 47%, and reduced total cholesterol by about 19% and Low-density lipoprotein by about 22%.
   Sci Rep, 2025 · checked 2026-10-02
9. cxl-r3-08 · meta-analysis
   High intake of broccoli and cabbage was associated with a decreased risk of gastric cancer (RR: 0.64; 95% CI: 0.47-0.87) and gallbladder cancer (RR: 0.46; 95% CI: 0.29-0.75).
   Crit Rev Food Sci Nutr, 2024 · checked 2026-10-02
10. cxl-r3-09 · meta-analysis
    When all studies were pooled, we yielded a significantly inverse association between CV (relative risk = 0.81; 95% confidence interval, 0.75-0.88) intake and gastric cancer risk, with little heterogeneity (Q = 27.27, P = 0.292, I(2) = 12.0%). Specific analysis for cabbage intake yielded similar result.
    Cancer Sci, 2013 · checked 2026-10-02
11. cxl-r3-10 · meta-analysis
    The meta-analyses performed demonstrated a significant effect on CYP1A2 and glutathione S-transferase-alpha (GST-α), with consumption of Cruciferae increasing the activities of these enzymes by 20-40% and 15-35%, respectively.
    Clin Pharmacol Ther, 2020 · checked 2026-10-02
12. cxl-r3-13 · meta-analysis
    Lettuce (61.0%), salad (57.4%), spinach (54.2%), and cabbage (52.9%), were the vegetables most contaminated by parasites, while salad (73.8%), green pepper (35.3%), lettuce (26.0%), and cabbage (20.0%), were the most contaminated by bacteria.
    BMC Infect Dis, 2025 · checked 2026-10-02
13. cxl-r3-14 · meta-analysis
    Lettuce was the most contaminated (20.43%; 3,084/15,095).
    Rev Bras Parasitol Vet, 2024 · checked 2026-10-02
14. cxl-r3-15 · meta-analysis
    This analysis showed that the pooled HuNoVs prevalence in vegetables was 7 % (95 % confidence interval (CI): 3-13) worldwide. The continent with largest number of studies was Europe, and the highest number of samples was lettuce.
    Int J Food Microbiol, 2024 · checked 2026-10-02
15. cxl-r3-17 · registry entry
    POL-HC-6819 Brassicaceae (Cruciferae) (Common Name : Botanical family that include broccoli, couliflower, cabbage, Bruxelles sprouts etc.) Are particularly rich of protective compounds that protect cells and DNA from oxidative damage/are particularly rich of compounds that help our body to eliminate toxic substances Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6819, snapshot 2026-09-21 · checked 2026-10-02
16. cxl-r3-11 · case report
    She sustained a myocardial infarction five weeks after beginning a diet of lettuce, broccoli, and turnip greens to lose weight.
    Arch Intern Med, 1984 · checked 2026-10-02
17. cxl-r3-16 · cohort baseline
    Greater intake of other vegetables was associated with lower odds of metabolic acidosis (highest vs. lowest intake: adjusted odds ratio = 0.28, 95% confidence interval: 0.10, 0.79, P = 0.016)
    BMC Nephrol, 2026 · checked 2026-10-02