Cruciferous Vegetables and PCOS: The Fibre, Sulforaphane and DIM Math

How Many Cups of Broccoli or Cabbage Match a DIM Supplement?

None, in any realistic sense — the raw-vegetable amount needed runs from roughly 9,000 cups to well over 200,000 cups a day, depending on which vegetable and which conversion estimate is used. That gap between “contains the precursor” and “delivers the dose” is the actual answer to whether cruciferous vegetables are good for PCOS on DIM grounds: they are a legitimate food source of a compound DIM supplements are built from, but they cannot substitute for a DIM capsule in the amount any trial has tested. The arithmetic behind that claim is below, built entirely from published glucobrassicin content and one human study that measured how much of it actually turns into DIM — not a guess, and not marketing copy from either side of the supplement aisle.

This matters for a specific reason: DIM supplements are marketed for PCOS partly because DIM comes from cruciferous vegetables — a claim covered in full on the DIM supplement’s own thin evidence base — which makes “just eat more broccoli” sound like a free upgrade to the same effect. The calculation below tests that idea directly rather than assuming it.

Where Does the 108mg Trial Dose Actually Come From?

One hundred and eight milligrams a day is the only precisely-dosed human DIM figure that exists, from a 2004 pilot trial in 19 postmenopausal breast-cancer survivors that gave 10 women 108mg of a controlled-release DIM formulation (BioResponse-DIM) daily for 30 days against 9 on placebo. It is not a PCOS trial and it is not a dose anyone has shown to do anything for PCOS specifically — the full evidence gap is covered on this site’s DIM supplement page, not repeated here. It is used here purely as a fixed, real-world reference point: a number a supplement bottle actually contains, expressed in molar terms so it can be compared against how much glucobrassicin a vegetable contains. In moles, 108mg of DIM (molecular weight 246.3g/mol) works out to about 438 micromoles — the target the rest of this calculation works backward from.

How Much Glucobrassicin Is Actually in Raw Broccoli, Cabbage and Brussels Sprouts?

Brussels sprouts carry roughly four times more glucobrassicin than cabbage, gram for gram, in the one study that measured both under controlled feeding conditions. A 2014 randomised crossover trial in 25 healthy adults measured the exact glucobrassicin concentration of the raw vegetables it fed subjects: 45.8 micromoles per 100g fresh weight in cabbage, and 183.9 micromoles per 100g fresh weight in Brussels sprouts. Broccoli was not part of that trial, but a separate 2018 analysis of broccoli floret tissue measured glucobrassicin at 1.54 micromoles per gram of dry weight, in florets that were 86% water by weight — converting that to the same fresh-weight basis as the other two puts broccoli at roughly 21.6 micromoles per 100g, lower than cabbage.

That content difference alone would already make Brussels sprouts the closest a vegetable gets to a meaningful DIM source. It is the conversion step, not the vegetable, that turns all three numbers absurd.

How Much of That Glucobrassicin Actually Turns Into DIM?

Almost none of it, measured the only way it has ever been measured directly in living people. The same 2014 crossover trial fed subjects 50g of raw cabbage or raw Brussels sprouts daily for three days each and measured 3,3’-diindolylmethane excreted in their urine over the following 24 hours — the first study to link a specific glucobrassicin intake to a specific, measured DIM output in humans, rather than assuming a conversion rate from cell-culture chemistry. It found that DIM excretion averaged just 0.03% of the glucobrassicin consumed after Brussels sprouts, and 0.01% after cabbage. Urinary DIM was also significantly higher after Brussels sprouts than after cabbage — an average difference of 8.73 picomoles per milligram of creatinine — confirming the food itself, not noise, drove the difference.

Broccoli was not tested in that trial, so its true conversion yield is unmeasured. Because broccoli is the same species as cabbage and Brussels sprouts (Brassica oleracea, just a different cultivar group), extending the same 0.01–0.03% range to it is a reasonable extrapolation — not a measured fact, which is why Table 1 shows broccoli as a range rather than a single number.

The Full Calculation, Shown

Working from a 438-micromole DIM target, a 0.01% conversion yield, and cabbage’s 45.8-micromole glucobrassicin content: matching the dose requires about 4.38 million micromoles of glucobrassicin, which means roughly 9,570 kilograms of raw cabbage — using the standard USDA cup weight of about 89g for chopped raw cabbage, that is somewhere north of 100,000 cups in a single day. Running the identical arithmetic on Brussels sprouts, with its higher content and its higher measured yield (0.03%), needs about 1.46 million micromoles of glucobrassicin, or roughly 795 kilograms — still around 9,000 cups, but two orders of magnitude smaller than the cabbage figure because both content and yield work in its favour at once.

One more limitation worth stating plainly: this comparison sets an administered supplement dose (108mg ingested) against a urinary recovery percentage from food (DIM detected in urine, after losses). Those are not identical endpoints — some of a supplement’s DIM is likely also lost to metabolism before reaching urine, which would make the true equivalence somewhat more favourable to food than shown here, while any vegetable-derived DIM that gets absorbed and metabolised without ever appearing as intact urinary DIM would make it less favourable. The published data does not resolve which direction dominates. That uncertainty does not change the conclusion; it only means the true number could plausibly sit anywhere from several hundred to tens of thousands of kilograms a day, not that it collapses to something achievable.

Does Cooking or Prep Change Any of This?

Yes, and not in the direction that helps. A 2007 study measuring glucosinolates in broccoli, Brussels sprouts, cauliflower and cabbage found that boiling caused significant glucosinolate loss, with roughly 90% of what was lost ending up leached into the cooking water — while steaming, microwaving and stir-frying caused no significant loss. The same study found that finely shredded vegetables left to sit lost glucosinolates progressively over time, up to 75% within six hours of shredding, and that ordinary refrigerated storage over a week caused a smaller loss of 9–26%. This is why the calculation above deliberately used raw, freshly-prepared vegetables: it is the best-case scenario for glucobrassicin content, and the real number for anyone eating boiled or long-stored vegetables would be worse, not better.

What About Fibre and Blood Sugar?

Cruciferous vegetables earn their place in a PCOS diet through fibre and glycaemic behaviour, not through DIM. A cup of cooked broccoli carries a meaningful amount of fibre for very little carbohydrate, which is exactly the low-glycaemic-load profile the daily fibre target for PCOS is built around — that page covers the actual gram target, the soluble-versus-insoluble distinction, and a full food table, and none of it is repeated here. The practical takeaway for this article is narrower: broccoli, cabbage, cauliflower, kale and Brussels sprouts belong on a PCOS plate on fibre and volume alone, independent of whatever DIM math applies to any of them. A full aisle-by-aisle PCOS shopping list already places this same vegetable group in the produce section for that reason, and the diet section covers every other food question this article deliberately leaves out. Fermented cabbage — kimchi specifically — is one cruciferous-vegetable form with its own separate gut-health angle this article does not cover.

What Has Sulforaphane Actually Been Shown to Do?

Sulforaphane, a different compound from a different glucosinolate (glucoraphanin, not glucobrassicin), has real human trial evidence behind it — but not in PCOS, and not at the amount a normal serving of mature broccoli provides. A 2017 randomised, double-blind, placebo-controlled trial gave 97 adults with type 2 diabetes a concentrated broccoli sprout extract supplying roughly 150 micromoles of sulforaphane daily for 12 weeks. It lowered fasting blood glucose and HbA1c, but only in the subgroup with poorly controlled diabetes at the start — participants with well-controlled blood sugar saw no meaningful change. Two things matter for a PCOS reader specifically: this trial was conducted in people with type 2 diabetes, not PCOS, so a mechanistic link (both conditions involve insulin resistance) is plausible but unproven in this population; and the extract used was made from broccoli sprouts, which concentrate glucosinolate precursors far more densely than the mature florets sold as broccoli in a grocery store, so this result does not describe what eating a normal broccoli side dish delivers.

You may also see PCOS referred to as polyendocrine metabolic ovarian syndrome (PMOS), the name a 2026 global consensus of more than 50 organisations gave the same condition. Nothing about the vegetable-chemistry evidence above changes under either name; this article uses PCOS because that is still what most readers search.

Who This Calculation Will Not Help

Anyone hoping this article justifies swapping a DIM supplement for a vegetable habit should read the numbers above as a “no”: the gap between a trial dose and a food source is not a small one to close with a bigger salad. It also will not settle whether DIM supplements themselves are worth taking for PCOS — that question depends on evidence this article does not cover, and the supplement’s own page answers it honestly instead. If you already avoid broccoli or cabbage because of a thyroid condition, whether cruciferous vegetables interfere with thyroid function is a separate question this article does not re-answer, and the short version is that ordinary intake is not the problem the internet often assumes it is. Nobody with an allergy to Brassica vegetables, or on a medication interacting specifically with vitamin K (found in meaningful amounts in these same vegetables), should treat this article’s food-versus-supplement comparison as clearance to sharply increase intake without checking that separately.

The 2023 international PCOS guideline does not address glucosinolates, DIM or sulforaphane specifically — it endorses no special diet composition for PCOS at all, cruciferous vegetables included, which leaves ordinary healthy-eating guidance, not a targeted dose, as the actual recommendation here.