Turnips: the randomised evidence is about the seed oil

The strongest evidence about turnips is not evidence about the root. Thirty-seven men aged 30 to 65 with metabolic syndrome swapped 37.5 g of butter a day for 35 mL of cold pressed turnip rapeseed oil for 6 to 8 weeks. Total cholesterol fell 8 percent and LDL cholesterol 11 percent against the butter period, in an open label single centre crossover trial in men only. The oil is pressed from turnip rape seed and the comparator was butter, so what moved the numbers was trading saturated fat for unsaturated fat. The root was never tested. A substudy of those same 37 men found the 7.2 percent fall in serum cholesterol was not explained by cholesterol absorption, synthesis or PCSK9, which leaves the mechanism open and adds no independent confirmation. For the vegetable itself the best on offer is observational. In a pooled case-control study from northwestern Spain, covering 438 lung cancer cases and 781 controls who had all never smoked, eating turnip tops one to six times a week went with 52 percent lower odds of lung cancer, odds ratio 0.48 with a confidence interval of 0.34 to 0.66. Those are odds rather than risk, diet was recalled after diagnosis, and the same paper put tomatoes, carrots and potatoes on the harmful side, which is hard to read as biology. Turnip tops are the leaves.

The numbers, per 100 g

How much is actually in it

• Across eight Foundation Foods samples of raw turnip, folate ranged from 42.17 to 77.5 micrograms per 100 g and calcium from 22.5 to 48.7 mg, so the single catalogue number sits inside a spread of 59 to 80 percent. — Eight laboratory samples of raw turnip root, USDA Foundation Foods (n = 8 samples) Evidence D source
  Folate 60.24 ug mean, range 42.17-77.5 (spread 59%); calcium 32.7 mg mean, range 22.5-48.7 (spread 80%); copper spread 253%
• The US and UK composition tables disagree about the same vegetable: raw turnip carries 26.78 mg of vitamin C and 60.24 micrograms of folate in USDA data against 17 mg and 14 micrograms in the UK table, a gap of 37 and 77 percent. — Reference records for raw turnip root in two national composition tables (n = 2 datasets) Evidence D source
  Vitamin C 26.78 vs 17 mg (37% apart); folate 60.24 vs 14 ug (77% apart); vitamin B6 0.118 vs 0.08 mg (32% apart)

What a real portion looks like

• One whole turnip weighs about 120 g and a cup of raw slices about 130 g, so the usual helping is close to the 100 g the tables are written for, while a cup of mashed cooked turnip is 235 g. — Household measures recorded for turnip in the US food coding survey (n = 8 measures) Evidence D source
  Raw: 1 slice 15 g, 1 whole 120 g, 1 cup 130 g; cooked: 1 whole 120 g, 1 cup 160 g, 1 cup mashed 235 g

What your body absorbs

• A systematic review of 18 studies counted 129 phytochemicals in turnip greens, including 19 glucosinolates and 59 polyphenols, and states that their bioavailability, transport and metabolism after eating still need to be investigated. — 18 included studies of turnip green samples out of 5077 citations screened, no human outcome data (n = 18 studies) Evidence D source
  129 compounds reported (19 glucosinolates, 33 breakdown products, 10 organic acids, 59 polyphenols); gluconapin most common across five studies; half the included studies gave no concentrations

What cooking and storage change

• Boiling root vegetables in water that covers them and draining keeps 65 percent of vitamin C and 65 percent of folate, while boiling in little water keeps 70 percent of both, so the cooking water decides about a third of the loss. — Retention factors assigned to the group Vegetables and Vegetable Products, methods for roots (n = 2 methods) Evidence D source
  Water cover, drained (code 3455): vitamin C 65%, folate 65%, thiamin 80%, potassium 90% retained; little water, drained (code 3454): vitamin C 70%, folate 70%, thiamin 85%, vitamin B6 95% retained

What it does to your health

• Eating turnip tops one to six times a week went with 52 percent lower odds of lung cancer among never smokers, odds ratio 0.48 with a confidence interval of 0.34 to 0.66, compared with less than once a week. — 438 lung cancer cases and 781 controls, all never smokers, five pooled case-control studies in northwestern Spain (n = 1219) Evidence C source
  OR 0.48 (95% CI 0.34-0.66) for turnip tops eaten one to six times per week versus less than once a week; these are odds, not risk
• Swapping 37.5 g of butter a day for 35 mL of cold pressed turnip rapeseed oil over 6 to 8 weeks lowered total cholesterol by 8 percent and LDL cholesterol by 11 percent in 37 men with metabolic syndrome. That oil is pressed from Brassica rapa seed, and the turnip root was never tested. — 37 men aged 30 to 65 with metabolic syndrome, crossover periods of 6 to 8 weeks separated by an 8 week washout (n = 37) Evidence B source
  Total cholesterol -8% (p<0.001), LDL cholesterol -11% (p<0.001), oxidised LDL -16% (p=0.024) against the butter period; arterial elasticity unchanged
• The 7.2 percent fall in serum cholesterol on turnip rapeseed oil was not explained by cholesterol absorption, synthesis or PCSK9, even though the oil added 217 mg of plant sterols a day. — 37 men with metabolic syndrome, same crossover trial, sterol markers measured at the end of each 6 to 8 week period (n = 37) Evidence B source
  Serum cholesterol 7.2% lower on the oil period; synthesis and absorption markers and PCSK9 unchanged; plant sterol intake 217 mg/day from the oil versus 0.6 mg from butter

Safety, limits and interactions

• A woman of 35 on warfarin for a prosthetic aortic valve had a myocardial infarction five weeks after starting a weight loss diet of lettuce, broccoli and turnip greens, because vitamin K in those leaves works against the drug. — One 35 year old woman on warfarin sodium after aortic valve replacement (n = 1) Evidence D source
  Warfarin resistance and myocardial infarction after five weeks of a vitamin K rich leaf diet; no dose of greens reported
• Foodborne botulism was diagnosed in Italy after a man ate home preserved turnip tops in oil, with botulinum toxin found in his serum and toxigenic organisms in stool and in the leftover food. — One young adult man, Italy (n = 1) Evidence D source
  Botulinum toxin detected in sera and neurotoxigenic organisms in stools and leftover food after eating home preserved turnip tops in oil
• A meta-analysis of soil and vegetable measurements names turnip among the vegetables whose intake carries a potential health risk on thallium polluted soil, and puts the safe soil threshold for root and stalk vegetables between 0.92 and 6.06 mg per kg depending on pH. — 35 vegetable species grown on soils of varying thallium content and pH, pooled field measurements (n = 35 species) Evidence D source
  Derived soil thallium thresholds 1.46-6.72 mg/kg for all vegetables, 1.74-5.26 for leafy and 0.92-6.06 for root and stalk; turnip listed among species whose ingestion poses potential health risks

What people believe that the data does not support

• Where goitre affected more than 30 percent of schoolgirls, a comparison of 284 girls with goitre and 288 without found no difference in reported turnip, kale or soya intake, and the risk factors that did stand out were open salt containers and district of residence. — 1050 primary school girls examined in Qom, Iran, 2002; 284 cases with goitre and 288 randomly selected controls, mean age 8.7 and 8.9 years (n = 572) Evidence C source
  No significant difference in history of soya, kale or turnip between cases and controls; storage of iodised salt in open containers OR 2.201 (1.412-3.428)

Who this works differently for

• Among 1887 children screened for suspected food allergy, 206 or 10.9 percent reacted on skin prick testing to turnip rape or oilseed rape, and 25 of 28 tested further reacted on food challenge. — 1887 children with atopic dermatitis screened; 28 with a wheal of 5 mm or more challenged; 25 children with atopic dermatitis and negative tests as controls (n = 1887 screened, 28 challenged) Evidence C source
  206 of 1887 (10.9%) sensitised; 25 of 28 (89%) positive on challenge, 17 with labial whealing and 8 with facial urticaria, eczema flare or abdominal symptoms; all 25 controls negative
• In 106 people in Jeddah, where 85 percent of controls and 83 percent of cases were iodine deficient, urinary iodine tracked reported turnip intake among hypothyroid cases with a correlation of 0.280. — 106 subjects recruited at a university hospital in Jeddah, hypothyroid cases and controls, dietary goitrogens by questionnaire (n = 106) Evidence C source
  Urinary iodine concentration associated with dietary turnip among cases, r = 0.280, p < 0.05; iodine deficiency in 85% of controls and 83% of cases

What is still unknown

• Turnip intake showed no link with new metabolic syndrome in 3616 adults followed for about two years, with an odds ratio of 1.23 and limits of 0.68 to 2.23. The conventional model on the same data gave 2.48, with limits from 0.82 to 7.52. — 3616 healthy Iranian adults aged 20 and over, free of metabolic syndrome at baseline, median follow-up 24.6 months, Tehran Lipid and Glucose Study (n = 3616) Evidence C source
  OR 1.23 (0.68 to 2.23) by Bayesian multilevel model versus OR 2.48 (0.82 to 7.52) by full logistic regression; both intervals include 1, so no association is shown either way

The bottom line

Buy turnips because they are cheap and you like them. A whole raw turnip weighs about 120 g and a cup of raw slices about 130 g, so an ordinary helping lands near the 100 g the tables are written for, while a cup of mashed cooked turnip is 235 g. Those weights come from the American survey database, and any nutrient figure per portion is arithmetic on the per 100 g value rather than a measured plate. How much sits in the root is a shakier question than one catalogue number suggests. Across eight laboratory samples of raw turnip in USDA Foundation Foods, folate ran from 42.17 to 77.5 micrograms per 100 g and calcium from 22.5 to 48.7 mg, a spread between samples of one dataset rather than between varieties anyone named. The US and UK reference tables put vitamin C at 26.78 mg against 17 mg and folate at 60.24 micrograms against 14, though matching those two records to the same product is our own reading, and cultivar, season and analytical method all differ. The cooking water decides about a third of the loss: 65 percent of vitamin C and 65 percent of folate are kept when roots are boiled under water that covers them and drained, and 70 percent of both when the water is scant. Those retention factors are assigned to the whole class of vegetables by cooking method, never measured on turnip, and the table behind them dates from 1975. The cautions here are real, and each one sits slightly to the side of the root. Turnip greens are the leaves, and the vitamin K in such leaves works against warfarin. A 35 year old woman with a prosthetic aortic valve had a myocardial infarction five weeks into a weight loss diet of lettuce, broccoli and turnip greens together. That is one case from 1984 with no quantity of greens written down, so it shows the direction of the interaction and nothing about how much is too much. Home preserved turnip tops in oil gave one young man in Italy foodborne botulism, with toxin confirmed in his serum, and that hazard belongs to any low acid vegetable put under oil in a home kitchen. In children the allergen is the seed. Among 1887 children with atopic dermatitis, 206 or 10.9 percent had a positive skin prick test to turnip rape or oilseed rape, and 25 of 28 who went on to a food challenge reacted, on an open challenge that was not randomised. Thallium is a question about the soil a turnip grew in, and that meta-analysis measured no produce on sale. The goitre story has been tested once, in one place, and there it did not hold. In Qom, Iran, 284 schoolgirls with goitre and 288 without reported the same intake of turnip, kale and soya, and what did stand out was iodised salt stored in open containers, odds ratio 2.201 with limits of 1.412 to 3.428. That questionnaire recorded no quantities, and the null belongs to a country where iodised salt reached over 95 percent of households. A case-control study of 106 people in Jeddah found urinary iodine rising with reported turnip intake, correlation 0.280, which runs opposite to the goitrogen story, in a group where 83 to 85 percent were already iodine deficient. Two questions stay open. Turnip intake showed no link with new metabolic syndrome among 3616 Iranian adults followed about two years, odds ratio 1.23 with limits of 0.68 to 2.23, in a paper whose subject was statistical method rather than turnip. And a systematic review of 18 studies counted 129 phytochemicals in turnip greens, then said their bioavailability and metabolism after eating still need to be investigated.

Sources

1. trnp-r5-01 · food composition dataset
   Turnips, raw | Folate, total 60.24 UG, range 42.17-77.5, median 58.41, samples 8 | Calcium, Ca 32.7 MG, range 22.5-48.7, median 31.05, samples 8 | Copper, Cu 0.022 MG, range 0.0-0.0557, samples 8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 (Turnips, raw, FDC 2747674) · checked 2026-09-24
2. trnp-r5-02 · food composition dataset comparison
   Turnip, flesh only, raw [13-389]: vitamin C 17 mg, folate 14 ug, vitamin B6 0.08 mg per 100 g
   CoFID 2021, Public Health England / OGL v3.0 (Turnip, flesh only, raw, 13-389) against USDA FoodData Central Foundation Foods, release 2026-04-30 · checked 2026-09-24
3. trnp-r5-04 · portion size dataset
   Turnip, raw (fdc_id 2709809): 1 slice 15 g, 1 whole 120 g, 1 cup 130 g, quantity not specified 65 g | Turnip, cooked (fdc_id 2710002): 1 whole 120 g, 1 cup 160 g, 1 cup mashed 235 g, quantity not specified 80 g
   USDA FNDDS, Turnip, raw (FDC 2709809) and Turnip, cooked (FDC 2710002) · checked 2026-09-24
4. trnp-r5-13 · systematic review of food composition studies
   We found 129 phytochemicals (19 glucosinolates, 33 glucosinolate-breakdown products, 10 organic acids and 59 polyphenolic compounds) reported in Turnip greens...However, detailed investigation on the pure compounds derived from Turnip green, their bioavailability, transport and metabolism after consumption is further needed.
   PLoS One, 2021 · checked 2026-09-24
5. trnp-r5-03 · nutrient retention dataset
   VEG,ROOTS,ETC,BLD,DRAIND,WTR COVER (Retn_Code 3455): vitamin_c_mg 65%, folate_total_ug 65%, thiamin_mg 80%, potassium_mg 90% | VEG,ROOTS,ETC,BLD,DRAIND,LITTLE WTR (Retn_Code 3454): vitamin_c_mg 70%, folate_total_ug 70%, thiamin_mg 85%, vitamin_b6_mg 95%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), codes USDA-RETN-R6:3455 and USDA-RETN-R6:3454 · checked 2026-09-24
6. trnp-r5-05 · case-control study in humans
   A total of 438 cases and 781 controls were included...turnip tops (OR 0.48; 95%CI 0.34-0.66)
   Nutr Cancer, 2022 · checked 2026-09-24
7. trnp-r5-07 · randomised crossover trial in humans
   Compared to butter, administration of CPTRO was followed by a reduction of total cholesterol by 8% (p < 0.001) and LDL cholesterol by 11% (p < 0.001). The level of oxidized LDL was 16% lower after oil period (p = 0.024).
   Lipids Health Dis, 2010 · checked 2026-09-24
8. trnp-r5-08 · randomised crossover trial in humans, mechanistic substudy
   The reduction in serum cholesterol by 7.2% after consumption of rapeseed oil could not be explained by changes in cholesterol absorption, synthesis or PCSK9 metabolism in MetS.
   J Investig Med, 2018 · checked 2026-09-24
9. trnp-r5-10 · case report in a patient on warfarin
   She sustained a myocardial infarction five weeks after beginning a diet of lettuce, broccoli, and turnip greens to lose weight. Excess dietary vitamin K can cause life-threatening consequences in patients on warfarin treatment.
   Arch Intern Med, 1984 · checked 2026-09-24
10. trnp-r5-11 · case report of foodborne botulism
    In the case reported here, clinical diagnosis was performed on the basis of clinical signs and referred consumption of home-preserved turnip tops in oil.
    Ann Ist Super Sanita, 2015 · checked 2026-09-24
11. trnp-r5-12 · meta-analysis of field experiments on soil contamination
    the derived soil Tl thresholds for all, leafy and root-stalk vegetables increased with an increase in soil pH, and were in the range of 1.46-6.72, 1.74-5.26 and 0.92-6.06 mg/kg, respectively...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
12. trnp-r5-15 · case-control study in children
    There is no significant difference between the two groups regarding history of soya, kale, turnip, fish, daily iodized salt usage, education and job of mothers, monthly family income, nationality, immigration and residential situation.
    Eur J Clin Nutr, 2006 · checked 2026-09-24
13. trnp-r5-09 · non-randomised food challenge study in children
    Two-hundred and six (10.9%) children had positive SPT to turnip rape and/or oilseed rape. Twenty-five (89%) of 28 children showed a positive challenge reaction to turnip rape.
    Allergy, 2006 · checked 2026-09-24
14. trnp-r5-14 · case-control study in patients with hypothyroidism
    UIC was associated with dietary goitrogens including turnip (r = 0.280, p < 0.05) and pine (r = 0.289, p < 0.05) among cases.
    Biol Trace Elem Res, 2009 · checked 2026-09-24
15. trnp-r5-06 · prospective cohort study in adults
    3616 healthy Iranian adults...(3) turnip (1.23 (0.68 to 2.23) vs 2.48 (0.82 to 7.52))
    BMJ Open, 2018 · checked 2026-09-24