Nasturtium.

The isothiocyanates from nasturtium and watercress leaf, chiefly benzyl and phenethyl isothiocyanate, share a mechanism with sulforaphane from broccoli. Both are electrophiles that modify Keap1 cysteines and increase transcription of phase II detoxification enzymes. Combining them raises total isothiocyanate exposure rather than adding a separate mechanism. This is mechanistic reasoning, not an outcome measured for the pair.

Glucosinolates are stable and largely inert until myrosinase hydrolyses them. Products that pair a glucosinolate source with retained plant myrosinase convert more of the load than heat-processed material does. Pairing two glucosinolate sources raises substrate, and the conversion step remains the limiting factor.

Cooking or hot-air drying inactivates the plant enzyme, so conversion then depends on colonic bacteria. Several common gut species hydrolyse glucosinolates, and conversion varies widely between people. A probiotic does not guarantee conversion, and the size of the effect in humans is not settled.

Green leafy plants carry nitrate that oral bacteria reduce to nitrite. In gastric acid, ascorbate drives the further reduction of nitrite to nitric oxide instead of allowing nitrosation chemistry. The chemistry is settled. Whether the pairing changes anything a person notices is a separate question.

Watercress and other Brassicaceae leaves sit in the moderate to high nitrate band, and beetroot is the usual concentrated source. Taken together they raise total nitrate load rather than acting on different targets. Anyone tracking nitrate intake for a clinical reason should count both.

Some glucosinolate degradation routes yield thiocyanate ion, which is a recognised competitive inhibitor of iodide uptake into the thyroid. The competition matters most when iodine intake is already low. At ordinary culinary intakes with adequate iodine it is a labelling point rather than a practical problem.

The mercapturic acid pathway is the main route of isothiocyanate clearance, and glutathione is consumed in the first step. Glutathione S-transferase genotype changes how fast that clearance runs, which is one reason human responses to cruciferous intake differ. Read this as pharmacology, not as a reason to take the two together.

Phylloquinone sits in the chloroplast, so dark green leaves carry meaningful amounts. Anyone whose vitamin K intake is monitored by a clinician should count leaf intake alongside a supplement rather than only the capsule. The point is consistency of intake, not avoidance.

Lutein, beta-carotene and phylloquinone all partition into mixed micelles, and micelle formation depends on dietary fat and bile. A leaf eaten with no fat at all gives up much less of these compounds. Any fat source works. The medium chain triglyceride is convenience rather than a special property.

Watercress grown in selenium-containing water can carry selenomethionine and related forms, so raw material selenium content is not fixed. Both selenium status and isothiocyanates feed into cellular antioxidant defence, though by different routes. Treated as a compositional note, not a demonstrated combination effect.