Sulforaphane Foods: Where It Comes From, and How Not to Destroy It

The short answer

No food contains sulforaphane. Cruciferous vegetables contain glucoraphanin, a glucosinolate, stored separately from the enzyme myrosinase that converts it. Chewing, chopping, or crushing the tissue brings them together and sulforaphane appears within seconds. This is why the question is not really “which foods have sulforaphane” but “which foods carry the most glucoraphanin, and what did you do to them before eating.”

Three-day-old broccoli sprouts are the outlier by a wide margin, carrying 10 to 100 times the glucoraphanin of mature broccoli of the same variety. After that it is broccoli, broccolini, brussels sprouts, then cabbage and kale, whose better cultivars can rival broccoli. And the single biggest thing you control is heat: boiling destroys myrosinase and leaches glucosinolates into the water, while raw or briefly steamed vegetables keep both. For the mechanism behind why any of this matters, see how sulforaphane activates Nrf2.

The two-part system in every cruciferous vegetable

Glucosinolates are the plant’s stored chemical defense. Glucoraphanin, the one that yields sulforaphane, sits inert in the vegetable’s cells. Myrosinase is kept physically apart, in separate cells. When an insect bites the leaf, the compartments rupture, the enzyme reaches the substrate, and pungent isothiocyanates are released to deter the attacker. Cutting a broccoli floret does exactly what the insect does.

Two consequences follow, and they explain almost everything about eating for sulforaphane. Damage to the plant is necessary, so swallowing broccoli whole is worse than chewing it thoroughly. And the enzyme is a protein, so anything that denatures proteins removes your ability to make sulforaphane at all, no matter how much glucoraphanin the vegetable started with.

Broccoli sprouts, and why they are not just small broccoli

In 1997 a Johns Hopkins group measured glucoraphanin in three-day-old broccoli sprouts against the mature plant grown from the same seed and found the sprouts carried between 10 and 100 times more. That finding is the reason broccoli sprouts exist as a health food at all, and it has held up: glucosinolate concentration is highest in the first days of germination and falls as the plant grows and its mass increases.

Sprouts have a second advantage that gets less attention and matters more than the concentration. They are eaten raw, so their myrosinase is fully intact. That makes fresh sprouts the one dietary source where both halves of the system arrive together and undamaged, which is precisely the thing that most supplements struggle to deliver.

The honest caveat is food safety. Raw sprouts are grown in warm, humid conditions that suit bacteria as well as seeds, and they have been linked to foodborne illness outbreaks repeatedly. Public health agencies advise that young children, older adults, pregnant people, and anyone immunocompromised avoid raw sprouts. That is a real caveat, not a formality, and it applies whether you buy them or grow them at home.

⚠ CLAIM (wellness): Raw sprouts carry a documented foodborne illness risk and are not recommended for people who are pregnant, immunocompromised, very young, or elderly. This is a food safety statement drawn from public health guidance, not medical advice about your situation. Lane: wellness-guidance.

The rest of the family, ranked honestly

Published figures vary a lot between studies, because cultivar, growing conditions, season, and storage all move glucosinolate content, and because labs measure different things (glucoraphanin content versus realized sulforaphane yield). Treat any single number, including the ones below, as an order of magnitude rather than a value you can bank.

Food	Roughly what it gives you	Notes
Broccoli sprouts (3 day)	By far the highest, 10 to 100x mature broccoli	Raw, so myrosinase intact. Food safety caveat applies.
Broccoli	Raw broccoli commonly yields on the order of 1 to 5 mg sulforaphane per 100 g	The benchmark. Highly cultivar-dependent.
Broccolini	Reported around 2.5 mg per 100 g	Comparable to or above standard broccoli in some analyses.
Brussels sprouts	Among the higher yielders after broccoli	Usually cooked, which is where most of it is lost.
Cabbage	Generally lower, but the best cultivars rival broccoli	Red and savoy varieties vary widely.
Kale	Around 0.8 mg per 100 g in one analysis	Some cultivars measure much higher. Popular reputation exceeds typical content.
Cauliflower, bok choy	Modest glucoraphanin	Contribute, but not sources you would target.
Watercress, radish, arugula, mustard greens	Rich in isothiocyanates, but not sulforaphane	See below. This distinction is widely fudged online.

The distinction most articles get wrong

Sulforaphane is one isothiocyanate among many, and each glucosinolate yields its own. Watercress is genuinely rich in glucosinolates, but its main product is phenethyl isothiocyanate, not sulforaphane. Radish and arugula yield sulforaphene and erucin, which are structurally related but not the same molecule. Mustard greens yield allyl isothiocyanate, the compound responsible for the burn in mustard and wasabi.

These are all interesting compounds with their own research literature, and eating them is a good idea. But if you are eating watercress specifically to get sulforaphane, you are not getting much sulforaphane. Only glucoraphanin yields sulforaphane, and glucoraphanin is concentrated in the broccoli branch of the family.

Cooking: the part you actually control

Myrosinase is destroyed by heat well before the glucoraphanin is. That produces a specific and slightly counterintuitive outcome: heavily cooked broccoli can still be full of glucoraphanin while yielding almost no sulforaphane, because the machinery to convert it is gone.

Boiling is the worst option, twice over. It denatures the enzyme, and glucosinolates are water-soluble, so a meaningful share leaches into water you then pour down the sink. Steaming and stir-frying preserve substantially more, which researchers attribute largely to the absence of direct contact with cooking water. Brief steaming, in the range of one to three minutes, is the usual recommendation: enough to soften, not enough to fully denature the enzyme. Keeping cooking temperatures below roughly 285°F (140°C) also limits glucosinolate degradation.

The chop-and-wait trick is real. Cut the broccoli, then leave it for around 40 minutes before cooking. The damaged tissue converts glucoraphanin to sulforaphane while the enzyme is still alive, and sulforaphane itself tolerates subsequent heat better than the enzyme does. You are letting the reaction finish before you kill the catalyst.

Frozen broccoli is a special case. Commercial freezing involves blanching, which is specifically designed to inactivate enzymes, so frozen broccoli typically arrives with its myrosinase already destroyed. It still contains glucoraphanin. It just cannot do anything with it on its own.

The mustard seed rescue

There is a genuinely useful fix for cooked and frozen brassicas, and it comes from the same enzyme chemistry. Mustard seed carries its own robust myrosinase, and adding mustard seed powder to already-cooked broccoli restores sulforaphane formation, because the exogenous enzyme does the job the vegetable’s own enzyme can no longer do. This was demonstrated in food chemistry work on cooked broccoli, and the same principle shows up in supplement formulation, where a randomized crossover study found mustard-derived myrosinase roughly doubled sulforaphane bioavailability from a glucoraphanin extract.

Practically: a small amount of mustard powder, horseradish, wasabi, or raw radish stirred into cooked cruciferous vegetables is not a folk remedy. It is the same reaction, supplied from outside. Raw broccoli sprouts sprinkled over cooked broccoli work the same way.

Your gut bacteria are a backup, not a plan

If you eat glucoraphanin with no active myrosinase at all, some conversion still happens, because certain gut bacteria carry myrosinase-like activity. This is why frozen broccoli is not entirely pointless. But the conversion rate is low and it varies enormously between people depending on microbiome composition, which is exactly the kind of variability you do not want sitting between you and a compound you are eating deliberately. Treat bacterial conversion as a floor, not a strategy.

How much food is a supplement dose?

Human trials have generally used intakes on the order of 40 to 100 µmol of sulforaphane per day, roughly 7 to 18 mg. At 1 to 5 mg per 100 g, hitting the middle of that range from raw broccoli alone would mean eating a great deal of raw broccoli, in the region of several hundred grams a day, and considerably more if you cook it conventionally.

A modest portion of fresh broccoli sprouts gets you into that territory far more easily, which is the entire argument for sprouts. But the sensible framing is not that food replaces a supplement or the reverse. It is that cruciferous vegetables several times a week, eaten raw or lightly steamed, deliver a steady and well-evidenced dietary pattern, while concentrated supplement doses are a separate decision with their own quality questions to work through. Food first is not a slogan here, it is just cheaper and safer.

The bottom line

Buy broccoli, chop it, wait, then steam it briefly. Add mustard powder if you have overcooked it or it came out of the freezer. If you want a genuinely concentrated dietary source, fresh broccoli sprouts are the only one that clearly qualifies, with a food safety caveat that some people should not ignore. And do not switch to watercress expecting sulforaphane, because it makes a different compound. Sulforaphane sits alongside other diet-first mitochondrial levers in our evidence-graded supplement guide, and works best as part of the broader picture covered in how to optimize your mitochondria.

Educational information only, not medical advice, and not evaluated by the FDA. Sulforaphane is not a treatment for any disease. Raw sprouts carry a foodborne illness risk; people who are pregnant, immunocompromised, very young, or elderly should follow public health guidance and avoid them. Talk to a clinician before making significant dietary changes, particularly if you take thyroid medication or anticoagulants, since cruciferous vegetables are also a notable source of vitamin K.