Rutabaga: a cabbage-family root studied mostly through its relatives

The firmest finding about this family is about your medicine cabinet. A meta-analysis of 23 human dietary intervention trials found that eating cruciferous vegetables raised CYP1A2 enzyme activity by 20 to 40 percent and glutathione S-transferase-alpha by 15 to 35 percent, which the authors say could alter drug exposure in people who regularly eat large or variable amounts of them. Those trials used broccoli, Brussels sprouts, cabbage, cauliflower, radish and watercress, they varied in dose and in how they measured enzyme activity, and their authors say the clinical significance is still unclear. That gap between the family and the root runs through this whole page. Our literature holds a single record under the name rutabaga. Everything below was measured on a relative, or on the glucosinolates the family shares, and each line says which. The composition table on this page is the one place the root itself is counted.

The numbers, per 100 g

How much is actually in it

• Root and stalk vegetables including turnip take up thallium from polluted soil, and a meta-analysis names them among the crops that pose a potential health risk where soil is contaminated. — 35 vegetable species across studies of soil thallium and vegetable uptake, pooled to derive soil thresholds (n = 35 species) Evidence C source
  Geomean thallium ordered leafy > root-stalk > solanaceous; derived soil thresholds 0.92 to 6.06 mg/kg for root-stalk vegetables; turnip listed among crops posing potential health risk

What your body absorbs

• Cooking destroys the enzyme that turns glucosinolates into sulforaphane, and adding 1 g of mustard powder to 200 g of cooked broccoli raised sulforaphane output more than fourfold in 12 adults. — 12 healthy adults, randomised crossover, 200 g cooked broccoli with and without 1 g powdered brown mustard, all urine collected for 24 hours (n = 12) Evidence B source
  Urinary sulforaphane metabolite 9.8 +/- 5.1 micromol per g creatinine without mustard versus 44.7 +/- 33.9 with it
• How much of a glucosinolate came back out as sulforaphane in 24 hour urine varied from 2% to 15% between ten people eating the same broccoli soup. — 10 participants, three-phase double blinded randomised crossover, 300 g of soup from broccoli of three Myb28 genotypes, plant myrosinase deliberately denatured (n = 10) Evidence B source
  Sulforaphane excreted over 24 hours 2 to 15% of the glucoraphanin eaten, independent of genotype; circulating sulforaphane threefold and fivefold higher with one or two Myb28V alleles

What cooking and storage change

• Across more than 100 studies of brassica processing, steaming preserved glucosinolates better than boiling or blanching. — over 100 articles on glucosinolate content and composition across brassica species and plant organs, with pre and post harvest processing (n = over 100 articles) Evidence C source
  Steaming judged the most favourable of boiling, blanching and steaming for preserving glucosinolates and their derivatives; highest content found in B. nigra at 201.95 +/- 53.36 micromol/g

What it does to your health

• Pooling 89 observational studies, the highest intake of cruciferous vegetables went with a 19% lower rate of gastrointestinal cancers than the lowest. — 81 articles covering 89 observational studies of cruciferous vegetable intake and gastrointestinal cancer (n = 89 studies) Evidence C source
  Rate ratio 0.81 (95% CI 0.76 to 0.87) highest versus lowest intake; below 75 g/day, each extra 50 g went with a 7% lower rate (RR 0.93, 95% CI 0.84 to 0.96); no association for gallbladder cancer
• A dose-response pooling of 17 studies and 97,595 patients put the odds of colon cancer at 0.8 for higher cruciferous vegetable intake. — 17 studies, 7 cohort and 10 case-control, 97,595 patients, literature searched to 28 June 2025 (n = 97,595) Evidence C source
  Odds ratio 0.8 (95% CI 0.72 to 0.90), with a non-linear dose-response showing progressively lower odds at higher intake

Safety, limits and interactions

• Pooling 23 human dietary intervention trials, eating cruciferous vegetables raised CYP1A2 enzyme activity by 20% to 40% and GST-alpha by 15% to 35%, which the authors say could alter drug exposure in people who regularly eat large or variable amounts of them. — 23 dietary intervention trials with drug metabolism endpoints in humans, vegetables including broccoli, Brussels sprout, cabbage, cauliflower, radish and watercress (n = 23 trials) Evidence B source
  CYP1A2 activity up 20 to 40%, glutathione S-transferase-alpha up 15 to 35%

What people believe that the data does not support

• A review of 123 studies found no support for the old claim that brassica vegetables suppress the thyroid in people, provided iodine intake is adequate. — 123 in vitro, animal and human studies of brassica plants and extracts, outcomes including thyroid mass and histology, TSH, T3, T4 and iodine uptake (n = 123 studies) Evidence C source
  No adverse effect on thyroid function reported for dietary intake with adequate iodine; goitrogenic mechanisms of glucosinolates and isothiocyanates described but not borne out in humans

What is still unknown

• An umbrella review of 22 meta-analyses covering 175 cancer studies concluded the evidence on cruciferous vegetables and cancer is still inconsistent and needs better methods. — 22 meta-analyses involving 175 independent cancer studies, quality graded with AMSTAR-2 and PRISMA 2020 (n = 22 meta-analyses) Evidence C source
  Associations suggested for lung, gastric, prostate, breast, endometrial, ovarian cancer and renal cell carcinoma, with evidence quality named as the limiting factor

The bottom line

Chopping and chewing a raw brassica sets off a plant enzyme, myrosinase, that converts glucosinolates into isothiocyanates such as sulforaphane. Cooking destroys it. In 12 healthy adults eating 200 g of cooked broccoli, adding 1 g of powdered brown mustard raised the urinary sulforaphane metabolite from 9.8 plus or minus 5.1 to 44.7 plus or minus 33.9 micromol per gram of creatinine over 24 hours. That is a urine marker after one meal each way in twelve people, not a health outcome, and the vegetable was broccoli. People also differ enormously from each other. Ten volunteers ate the same 300 g of broccoli soup and excreted between 2 and 15 percent of the glucoraphanin they swallowed as sulforaphane, independently of the broccoli genotype. For the cooking itself, a review of more than 100 brassica composition studies judged steaming the most favourable of steaming, boiling and blanching for keeping glucosinolates. It is a narrative synthesis with no pooled number, and its figures are per plant organ rather than per portion on a plate. The cancer numbers are observational and they are about the family. Pooling 89 observational studies, people in the highest category of cruciferous vegetable intake had a 19 percent lower rate of gastrointestinal cancers than those in the lowest (rate ratio 0.81, 95 percent CI 0.76 to 0.87). Below 75 g a day, each extra 50 g went with a 7 percent lower rate (RR 0.93, 95 percent CI 0.84 to 0.96), and there was no association for gallbladder cancer. A separate pooling of 17 studies and 97,595 patients put the odds of colon cancer at 0.8 (95 percent CI 0.72 to 0.90) for higher intake. Ten of those 17 were case-control studies, which ask people to remember what they used to eat, and odds are odds. An umbrella review of 22 meta-analyses covering 175 cancer studies says the evidence remains inconsistent, with study quality as the limiting factor and the same primary studies counted in several reviews at once. One old worry can be put down. A review of 123 in vitro, animal and human studies found no support for brassica vegetables suppressing the thyroid in people, as long as iodine intake is adequate. The iodine condition is doing real work in that sentence, and the human conclusion rests on the smaller human part of a mixed review. On caution, two things are worth carrying home. If you take a medicine cleared by CYP1A2 or by GST-alpha, large or variable amounts of cruciferous vegetables can alter your exposure to it, which is a question for your pharmacist rather than a reason to stop eating them. Second, a meta-analysis of 35 vegetable species found root and stalk vegetables accumulating thallium from contaminated soil, with turnip named among the crops that pose a potential health risk where soil is polluted. That is about polluted ground and a near relative rather than about this root from an ordinary shop. We found no study on allergy, on pregnancy or on children for this vegetable, and that silence is a hole in our evidence rather than a clearance.

Sources

1. ruta-r3-08 · meta-analysis of environmental measurements
   Vegetables from contaminated areas showed high Tl accumulation, and the geomean Tl content in different types of vegetables was in the following order: leafy > root-stalk > solanaceous vegetables...Ingestion of kale, beet, sweet potato, potato, taro, pepper, turnip, Chinese cabbage, eggplant and carrot poses potential health risks.
   Sci Total Environ, 2024 · checked 2026-09-24
2. ruta-r3-02 · randomised crossover trial
   When study subjects ingested cooked broccoli alone, mean urinary SF-NAC excreted was 9.8 ± 5.1 μmol per g creatinine, and when cooked broccoli was consumed with mustard powder, this increased significantly to 44.7 ± 33.9 μmol SF-NAC per gram creatinine.
   Mol Nutr Food Res, 2018 · checked 2026-09-24
3. ruta-r3-03 · randomised crossover trial
   Threefold and fivefold higher levels of sulforaphane occur in the circulation following consumption of Myb28V/B and Myb28V/V broccoli soups, respectively. The percentage of sulforaphane excreted in 24 h relative to the amount of glucoraphanin consumed varies among volunteers from 2 to 15%, but does not depend on the broccoli genotype.
   Mol Nutr Food Res, 2018 · checked 2026-09-24
4. ruta-r3-05 · systematic review
   The authors also conclude that food processing can influence significantly the final content of GLS, considering the most popular methods: boiling, blanching, steaming, the latter can be considered as the most favorable to preserve highest level of GLS and their deriviatives.
   Crit Rev Food Sci Nutr, 2021 · checked 2026-09-24
5. ruta-r3-06 · meta-analysis of observational studies
   In comparison to the lowest consumption categories, the highest consumption categories of CV were associated with a lower risk for all GI cancers [rate ratio (RR): 0.81, 95% confidence interval (95% CI) 0.76-0.87]. Compared to a CV intake of 75 g/day, subjects with CV intake <75 g/day experienced a 7% reduction in risk (RR: 0.93; 95% CI: 0.84-0.96) for each 50 g increase in consumption.
   Crit Rev Food Sci Nutr, 2024 · checked 2026-09-24
6. ruta-r3-07 · meta-analysis of observational studies
   Consumption of CV was found to be inversely correlated with CC risk (odds ratios [OR] = 0.8; 95% confidence interval [CI] 0.72-0.90) in the pooled analysis using a random-effects model. Furthermore, a progressive decrease in risk was shown by the non-linear dose-response analysis as consumption levels increased.
   BMC Gastroenterol, 2025 · checked 2026-09-24
7. ruta-r3-01 · meta-analysis of intervention trials
   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. The results herein suggest that patients undergoing pharmacotherapy with CYP1A2 or GST-α substrates could have altered drug exposure profiles if they regularly eat large or variable amounts of cruciferous vegetables.
   Clin Pharmacol Ther, 2020 · checked 2026-09-24
8. ruta-r3-04 · systematic review
   The vast majority of the results cast doubt on previous assumptions claiming that brassica plants have antithyroid effects in humans. Instead, they indicate that including brassica vegetables in the daily diet, particularly when accompanied by adequate iodine intake, poses no adverse effects on thyroid function.
   Int J Mol Sci, 2024 · checked 2026-09-24
9. ruta-r3-09 · umbrella review
   Overall, 22 meta-analyses involving 175 independent cancer studies were included...Future research should focus on improving methods and techniques, controlling influencing factors, elucidating underlying mechanisms, and improving evidence quality to demonstrate the association between CV intake and cancer.
   J Food Sci, 2024 · checked 2026-09-24