Broccoli does not contain ready-made sulforaphane. It forms when a precursor called glucoraphanin meets an enzyme called myrosinase, which only happens once cells are broken.
The catch is that this enzyme is heat-sensitive. Boil a whole head for a long time and the precursor survives while almost no sulforaphane forms. With broccoli, how you handle it matters more than what is in it.
Key benefits
Sulforaphane switches on detoxification enzymes
It activates the Nrf2 pathway, the cell's defence switch, increasing production of phase-two detoxification enzymes. This mechanism is the one most often cited to explain observational links between cruciferous vegetables and lower risk of some cancers.
More vitamin C than lemon
89 mg per 100 g beats lemon (53 mg) by weight. Because it is water-soluble, though, long boiling washes out nearly half. Steaming or a quick sauté keeps more.
Vitamin K for bone and clotting
100 g covers most of an adult's daily requirement. Vitamin K is needed to activate the proteins that direct calcium into bone.
Fibre for fullness and gut bacteria
2.6 g per 100 g at only 34 kcal — a high ratio. That makes broccoli an easy way to add volume to a meal without adding much energy.
How to eat it well
- Steam for three minutes or less. Steaming preserves far more sulforaphane and vitamin C than boiling.
- If you overcook it, add mustard or radish. Their myrosinase substitutes for the enzyme destroyed by heat.
- Eat the stem. Peeled, it is as tender as the florets and higher in fibre.
- Frozen broccoli is blanched before freezing, so it has no active enzyme. Pairing it with mustard makes up for that.
- Chopping it and waiting about 40 minutes before cooking lets sulforaphane form in advance, reducing heat losses.
What to watch out for
- On warfarin, keep vitamin K intake steady rather than increasing it suddenly.
- In hypothyroidism, large amounts of raw cruciferous vegetables can interfere with iodine uptake. Cooking largely resolves this.
- Raffinose and related oligosaccharides can cause gas and bloating in irritable bowel syndrome.
- If you have a history of kidney stones, avoid very large portions.
Nutrition
Approximate values per 100 g edible portion.
- Calories
- 34 kcal
- Carbohydrates
- 6.6 g
- Fiber
- 2.6 g
- Protein
- 2.8 g
- Fat
- 0.4 g
- Vitamin C
- 89 mg
- Vitamin K
- 102 µg
- Folate
- 63 µg
- Potassium
- 316 mg
Key nutrients
- Sulforaphane
- Vitamin C
- Vitamin K
- Folate
- Fiber