Nezam El-Tayebat Fact CheckA scientific assessment of the “نظام الطيبات” nutrition system
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Mostly false Overinterpreted Certainty of evidence: low provisional C-VEG-10

Raw cruciferous greens such as bok choy suppress the thyroid (glucosinolates) and can cause myxedema coma.

In short: This claim is mostly false as a general statement: eating normal amounts of cruciferous vegetables does not harm the thyroid when iodine intake is adequate; the reported myxedema coma followed months of 1-1.5 kg of raw bok choy a day in an elderly woman.
Conclusion: One extreme case does not show that crucifers harm the thyroid at normal intake.
  1. Original statement
  2. Scientific assessment
  3. Scientific evidence in detail
  4. In plain language
  5. Studies on this claim
  6. Regional context
  7. What applies in my country?
  8. References

Original statement

No Arabic original wording available.

Translation

Raw cruciferous greens such as bok choy suppress the thyroid (glucosinolates) and can cause myxedema coma.

Origin

Source status
Archive editors
Attribution
Archive editors
Origin
https://eltayebat.com/rule/leafy-greens-cucurbits/
Attribution uncertainty
Archive editorial text and study selection written by the archive operators, not necessarily by Elawady.
Claimed mechanism

Glucosinolate breakdown products inhibit iodine uptake.

Claimed health effect

Hypothyroidism, myxedema coma.

Population concerned

Everyone eating raw crucifers

Geographic restriction by Elawady

none found

Scientific assessment

Mostly false – Essential parts of the statement are not supported by the evidence or are strongly exaggerated.

Certainty of evidence: low – Further research is likely to change the assessment considerably.

1. What was claimed?

Raw crucifers cause severe hypothyroidism.

2. What is demonstrably correct?

A case of myxedema coma attributed to very high raw bok choy intake was published (Chu & Seltzer 2010).

3. What is wrong or exaggerated?

A single case at extreme intake cannot be generalised; cooking reduces glucosinolate activity (general knowledge, not verified here).

4. What remains unclear?

Threshold intake is unknown.

5. Which studies support it?

Chu & Seltzer 2010 (case).

6. Which studies contradict it?

Aune 2017 (cruciferous vegetables inversely associated with CVD, mortality and cancer).

7. What applies to Germany and Europe?

Not specific.

8. What is known about Egypt?

Not specific.

9. What practical conclusion is appropriate?

Normal intake of cruciferous vegetables is not a thyroid risk for people with adequate iodine.

Assessment details

Rationale for certainty of evidence

The evidence is a single case (NEJM letter) involving an 88-year-old woman; the archive's card states 'large quantities' daily. A single extreme case does not show a risk at normal intake; goitrogenic effects are mainly relevant with iodine deficiency (as Doerge 2002 notes for soy).

Source quality

Single case report; no PubMed abstract available, details taken from the archive card were not verifiable.

Regional transferability

Iodine status matters; Germany has iodised salt; Egypt has a salt iodisation programme (not reviewed).

Individual exceptions

People with iodine deficiency or existing hypothyroidism consuming very large raw amounts.

Regional scope of the claim
general (biological/medical)
Last reviewed
26 October 2026 provisional

Scientific evidence in detail

Overinterpreted – A real finding exists, but the claim draws more from it than the data allow (e.g. association taken as cause, animal data applied to humans, small effect presented as large).

Research question: Do raw cruciferous greens such as bok choy suppress thyroid function at usual intakes and cause myxedema coma?

Research question in detail (PECO)
Population
General population; people with iodine deficiency
Intervention or exposure
Raw brassica vegetables (glucosinolates, goitrin)
Comparison
Low intake
Geographic scope
iodine status-dependent
Outcomes
  • TSH/T4
  • hypothyroidism
  • goitre

Study results as reported by the authors. Our assessment follows below.

What speaks for the claim?

  • Thyroid crisis after raw bok choy

    Chu M, Seltzer TF. N Engl J Med 2010 · PMID 20484407 · DOI 10.1056/NEJMc0911005 Case series / case reportabstract checked

    Chu & Seltzer 2010 NEJM letter.

    Actual result
    Myxedema coma in an 88-year-old woman eating 1.0-1.5 kg raw bok choy daily for months.
    Methodological quality
    very low (single case)
    Relevance
    direct for extreme intake
    Limitations
    Single case, extreme dose.

    Original publication

  • Most brassicas carry little goitrogen

    Felker P et al.. Nutr Rev 2016 · PMID 26946249 · DOI 10.1093/nutrit/nuv110 Narrative reviewabstract checkednewly added

    Felker 2016 review.

    Actual result
    Collards, Brussels sprouts and some Russian kale contain enough goitrin to potentially reduce iodine uptake (>=194 umol); most others <10 umol/100 g.
    Methodological quality
    low
    Relevance
    indirect
    Limitations
    Industry-affiliated authors.

    Original publication

What speaks against the claim?

What does the overall evidence say?

Editorial assessment based on the studies above – not itself a study result.

Which position is better supported?

At usual intakes and adequate iodine, brassicas do not impair thyroid function; extreme raw intakes of certain varieties may contribute in susceptible people.

Why some studies weigh more

Systematic review outweighs a single case; dose and iodine status explain the case.

Is a causal relationship established? Possible, not established Plausible at extreme intakes; not at normal intakes.

Remaining uncertainty

Iodine-deficient populations.

Justified conclusion

Overgeneralised from one extreme case.

Does this depend on the country?
General biological effects
Universal.
Eating habits
n/a
Origin of the food
Goitrin content varies by variety.
Contaminants
n/a
National production conditions
n/a
Legal rules
n/a
Actual monitoring data
Egypt uses iodised salt; iodine status not reviewed.

A regional difference that changes the conclusion is not supported by robust data.

Statistical re-check
  • No pooled estimates – Not applicable. not recalculable from the published data
Certainty of the overall evidence (GRADE, simplified)
Main outcome
Thyroid dysfunction with usual brassica intake
Starting level
low (observational studies)
Reasons for downgrading
  • indirectness
Result
low

Simplified assessment by a single reviewer, following the GRADE approach; not a formal GRADE panel. GRADE rates the body of evidence for one outcome, not individual studies.

Search strategy

Documented literature searches for this review (search strings in the original database syntax).

DatabaseDateSearchLooking forHitsIncluded
PubMed26 October 2026(cruciferous OR brassica OR glucosinolate* OR goitrin OR "Brussels sprouts" OR kale) AND (thyroid OR hypothyroidism OR goiter OR TSH) AND humans[mh]supporting evidence100
Europe PMC26 October 2026(cruciferous OR brassica) AND (thyroid cancer OR hypothyroidism) AND ("meta-analysis" OR cohort OR trial)contradicting evidence952
PubMed26 October 2026(cruciferous vegetables) AND (thyroid cancer) AND (meta-analysis)contradicting evidence2

Open questions

Human trials in iodine deficiency.

How deeply was this checked?

4 linked studies: 1 checked in full text (1 of them with a structured risk-of-bias assessment), 3 on the basis of the abstract, 0 bibliographically only. No formal assessment with two independent reviewers and no independent human expert review has taken place yet.

Last scientific review: 26 October 2026

History of the verdict
  1. 25 October 2026 · Phase 1 · Initial assessment: Mostly false (low)
  2. 26 October 2026 · Phase 4 (systematic evidence review) · Re-examined with extended evidence; verdict unchanged: Mostly false (low)
    A 2024 systematic review supports the existing verdict; certainty stays low because human trials are few.
    New sources: I-VEG-127 I-VEG-128

In plain language

The archive cites one elderly woman who fell into a severe thyroid crisis after eating large amounts of raw bok choy every day. This is a single extreme case. Eating normal amounts of cabbage-family vegetables is not known to harm the thyroid in people who get enough iodine, and these vegetables are linked to lower disease risk in large studies.

Studies on this claim

Studies supporting the claim (1)

  • Thyroid crisis after raw bok choy

    Chu M, Seltzer TF. N Engl J Med 2010 · PMID 20484407 · DOI 10.1056/NEJMc0911005
    Case series / case reportcited by the Tayebat archiveabstract checked★ key study

    One elderly woman with extreme raw bok choy intake; no generalisation possible.

    Does the study support the specific claim? Partly · Methodological quality: very low · Certainty of evidence: see overall assessment of the claim

    Original publication · Scientific details

    Study explained simply
    What did the researchers want to find out?

    Report case

    How was the study done?

    Case letter

    How many people, animals or samples were studied?

    1

    What was actually found?

    Myxedema coma

    How large was the observed effect?

    Not applicable

    What do the results mean in everyday life?

    Extreme intakes can matter.

    What are the study's limitations?

    Single case

    What does it say about Elawady's specific claim?

    Very weak

    Do the results apply to Germany and Europe?

    Moderate

    What can explicitly not be concluded from this study?

    Cannot show risk at normal intake.

    Scientific details →

Studies contradicting or limiting the claim (2)

  • Fruit, vegetables and death rates

    Aune D et al.. Int J Epidemiol 2017 · PMID 28338764 · DOI 10.1093/ije/dyw319
    Meta-analysisindependent cross-checkfull text, structured risk-of-bias assessment★ key study

    Each extra 200 g of fruit and vegetables a day was linked to 10% lower death risk; green leafy vegetables and salads were also protective.

    Does the study support the specific claim? No · Methodological quality: high · Certainty of evidence: see overall assessment of the claim

    Original publication · Scientific details

    Study explained simply
    What did the researchers want to find out?

    F&V and outcomes

    How was the study done?

    Meta-analysis

    How many people, animals or samples were studied?

    95 studies

    What was actually found?

    Lower CVD, cancer, mortality

    How large was the observed effect?

    RR 0.90 per 200 g

    What do the results mean in everyday life?

    Eat plenty of vegetables.

    What are the study's limitations?

    Observational

    What does it say about Elawady's specific claim?

    Contradicts avoidance

    Do the results apply to Germany and Europe?

    High

    What can explicitly not be concluded from this study?

    Cannot prove causation.

    Scientific details →

  • Cabbage-family vegetables are not bad for the thyroid

    Galanty A et al.. Int J Mol Sci 2024 · PMID 38612798 · DOI 10.3390/ijms25073988
    Systematic reviewindependent cross-checkabstract checked★ key study

    A review of 123 studies concluded that daily brassica vegetables, especially with enough iodine, do not harm thyroid function.

    Brassica vegetables with adequate iodine do not impair thyroid function.

    Does the study support the specific claim? No · Methodological quality: low · Certainty of evidence: see overall assessment of the claim

    Original publication · Scientific details

    Study explained simply
    What did the researchers want to find out?

    Assess thyroid effects of brassicas.

    How was the study done?

    Systematic review.

    How many people, animals or samples were studied?

    123 articles.

    What was actually found?

    No adverse effect at dietary intakes with adequate iodine.

    How large was the observed effect?

    Not quantified.

    What do the results mean in everyday life?

    Normal amounts of cabbage, broccoli or bok choy are fine for the thyroid.

    What are the study's limitations?

    Mixed study types.

    What does it say about Elawady's specific claim?

    Contradicts the claim.

    Do the results apply to Germany and Europe?

    Applicable.

    What can explicitly not be concluded from this study?

    Cannot exclude effects at extreme raw intakes with iodine deficiency.

    Scientific details →

Studies with mixed or unclear results (1)

  • Most brassicas carry little goitrogen

    Felker P et al.. Nutr Rev 2016 · PMID 26946249 · DOI 10.1093/nutrit/nuv110
    Narrative reviewindependent cross-checkabstract checked

    Only a few varieties (collards, Brussels sprouts, some kale) contain enough goitrin to possibly reduce iodine uptake; broccoli and most kale contain little.

    Some brassicas contain enough goitrin to reduce iodine uptake at high intake; most minimal risk.

    Does the study support the specific claim? Partly · Methodological quality: low · Certainty of evidence: see overall assessment of the claim

    Original publication · Scientific details

    Study explained simply
    What did the researchers want to find out?

    Quantify goitrogen content of brassicas.

    How was the study done?

    Review.

    How many people, animals or samples were studied?

    Not applicable.

    What was actually found?

    Risk depends on variety and amount.

    How large was the observed effect?

    194 umol goitrin threshold.

    What do the results mean in everyday life?

    Very large amounts of certain raw brassicas could matter for people low in iodine.

    What are the study's limitations?

    Narrative; industry authors.

    What does it say about Elawady's specific claim?

    Partly supports a conditional version.

    Do the results apply to Germany and Europe?

    Applicable.

    What can explicitly not be concluded from this study?

    Cannot show harm at normal intakes.

    Scientific details →

Regional context

Germany / EU

Not specific.

Egypt

Not specific.

What applies in my country?

General scientific assessment

Mostly false One extreme case does not show that crucifers harm the thyroid at normal intake.

The following areas of food safety are relevant to this statement:

  • Pesticides and pesticide residues
  • Contaminants (heavy metals, PFAS, PCBs, dioxins, nitrate)
  • Pathogens (Salmonella, Campylobacter, etc.)

Fruit and vegetables

Choose a country to see the checked information for it.

Limits: legal rules describe what is allowed, not what every single food contains. Measurement data come from samples and are meaningful only together with their method details.

Country of residence or purchase Compare with another country

References

  1. Myxedema coma induced by ingestion of raw bok choy.. Chu M, Seltzer TF. N Engl J Med 2010 · PMID 20484407 · DOI 10.1056/NEJMc0911005
  2. Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality-a systematic review and dose-response meta-analysis of prospective studies.. Aune D et al.. Int J Epidemiol 2017 · PMID 28338764 · DOI 10.1093/ije/dyw319
  3. Do Brassica Vegetables Affect Thyroid Function?-A Comprehensive Systematic Review.. Galanty A et al.. Int J Mol Sci 2024 · PMID 38612798 · DOI 10.3390/ijms25073988
  4. Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism.. Felker P et al.. Nutr Rev 2016 · PMID 26946249 · DOI 10.1093/nutrit/nuv110

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