Watercress scored the highest of eighty-seven foods on the US nutrient-density index.
The peppery taste comes from glucosinolates, the same family of compounds found in mustard and rocket.
Buy cultivated watercress. Wild cress from a stream can carry liver fluke.
Shāhi grows in running water, which is where both its name and its problems come from. Its mustard bite wakes up a mouthful of bread and cheese. Gram for gram, it carries more vitamins and minerals per calorie than almost any other food measured. In Iran, it sits on the sabzi khordan plate beside tarragon, basil and radish, and people eat it by the fistful rather than the leaf.
Known to botanists as Nasturtium officinale.
Chapter 2 of 14
Why It Matters
Most people try to add nutrition by buying something new. But watercress is already on the Persian table, costs almost nothing, and delivers more per calorie than anything else on the plate. The habit is already there. You only need to eat it more often.
The vitamin K in watercress matters to your bones and blood, and older adults are the group most likely to be short of it. The catch is warfarin (a blood-thinning medicine): the same vitamin K works against the drug. That means keeping your intake steady rather than avoiding watercress, and talking with the person who prescribes it.
Supplies vitamin K, vitamin C and folate in a form people actually eat.
Chapter 3 of 14
What It Contains
Primary compounds
Glucosinolates (sharp-tasting compounds in cabbage-family vegetables) break down into isothiocyanates when the leaf is chewed. That reaction is the pepper you taste.
Phenethyl isothiocyanate is the most studied of them, mostly in laboratory work.
Beta-carotene and lutein (a yellow pigment linked to eye health) give the deep green colour and the vitamin A activity.
Other Constituents
Vitamin K sits high enough here to matter medically, which is unusual for a salad leaf.
Other notable constituents
Minerals: Calcium, Iron, Manganese · Fiber: About 0.2 g per cup — this is a nutrient leaf, not a fibre food
Chapter 4 of 14
What Studies in People Show
What studies in people show
Watercress ranked first among 47 powerhouse fruits and vegetables by nutrient density per calorie.Strong evidence
Watercress supplementation raised plasma carotenoids (the orange and yellow plant pigments your body can use) and reduced DNA damage markers in a small trial.Emerging evidence
Chapter 5 of 14
Preparation and Kitchen Use
With lunch or dinner, on the herb plate, every day it's in the fridge.
Rinse in several changes of cold water and shake dry.
Serve raw on the sabzi khordan plate.
Toss into salad with feta, walnut and olive oil.
Wilt into soup after the pot leaves the heat.
Blend into a herb sauce with parsley, garlic and lemon.
Eat it raw on the herb plate.
Pile it on the herb plate with feta, walnut and bread.
Stir it into soup off the heat, so it wilts rather than boils.
Chapter 6 of 14
Medicines and Interactions
General cautions
Medication interaction:
A cup carries several days' worth of vitamin K. If you take warfarin (a blood-thinning medicine), keep your intake steady and tell your clinician what it is.
Specific medicines
Medication interaction:
Warfarin — High vitamin K works directly against the drug. Consistency matters more than avoidance. (moderate concern)
Medication interaction:
Levothyroxine — As a cruciferous plant it's mildly goitrogenic in very large raw amounts. Ordinary eating isn't a concern. (low concern)
Chapter 7 of 14
Who Should Be Careful
General caution:
Wild watercress from a stream can carry liver fluke from grazing animals. Buy cultivated cress and wash it well.
General caution:
Large raw amounts can irritate a sensitive stomach. The old warning about eating it on an empty stomach is fair.
General caution:
Wild-harvested cress from livestock waterways.
Chapter 8 of 14
Pregnancy, Children and Older Adults
Pregnancy and breastfeeding
Pregnancy and breastfeeding:
Good in pregnancy for the folate and iron, with one firm rule: wash it thoroughly and buy cultivated cress rather than wild. Raw leaves from open water are the risk, not the plant.
Children
Children:
Most children find raw cress too sharp. Wilt it into soup or mix a few leaves through a milder herb plate, and let them come to the taste in their own time.
Older adults
Medication interaction:
A cheap, dense source of vitamins for someone eating small meals. The one caution that matters is warfarin, which is common in this age group and interacts directly with the vitamin K.
Chapter 9 of 14
Traditional Persian Perspective
Persian temperament: Hot & Dry (2nd degree). One of the few hot-natured greens. Hakims served it with cooling yoghurt or cheese to balance the bite.
Persian medicine sees shāhi as hot and dry, which is unusual for a leafy green. That helps explain why hakims used it to stir a sluggish appetite and clear what they called thick blood. The old texts also warn against eating too much on an empty stomach. Anyone who has tried a fistful before breakfast will recognise that as sound advice.
Hakims prescribed the crushed leaf as a spring tonic after a winter of stored food.
The juice was used as a wash for the scalp, an old and untested cosmetic use.
It was eaten with feta and walnut as the standard restorative for tiredness.
Chapter 10 of 14
What It Goes With
Pairing:
Feta
Salt and fat against pepper. This pairing is the whole reason the herb plate works.
Pairing:
Walnuts
Bitter, oily and rich beside a sharp leaf. Persians rarely serve one without the other.
Pairing:
Lavash
Wrap the cress and cheese in torn bread. That's the intended way to eat it.
Dairy:
Yoghurt
Cools the bite of a leaf the old texts called hot.
Chapter 11 of 14
Through the Year
Spring:
Spring
Best of the year. Tender, sharp, and the traditional spring plate.
Summer:
Summer
Still good, though heat makes it bolt and turn bitter.
Autumn:
Autumn
A second, milder crop. Good in soups as the nights cool.
Winter:
Winter
Mostly greenhouse-grown. Fine, but weaker in flavour.
Chapter 12 of 14
Questions People Ask
Is watercress really the most nutritious vegetable?
By the US density index, which scores nutrients per calorie, it came first out of eighty-seven foods. That's a real result, though it partly reflects how few calories watercress has.
Can I use rocket instead?
Yes. Rocket is in the same family and behaves the same way on the plate, though the pepper is different in character.
Why does mine go slimy in two days?
It was stored wet. Wash it just before eating and keep the rest dry in a bag with a paper towel.
Is wild cress safe?
Not reliably. Sheep and cattle pass liver fluke into the water it grows in. Cultivated cress avoids the problem entirely.
Chapter 13 of 14
Sources
Sad Giah Hezar Darman (صد گیاه و هزار درمان) — One Hundred Plants and One Thousand Remedies — Dr. Hossein Erfani, 4th edition (1375 / 1996–1997). Primary traditional Persian herbal reference cited throughout this platform. Presented as traditional knowledge, not as modern medical proof.
Office of Dietary Supplements: fact Sheets — US National Institutes of Health (NIH). https://ods.od.nih.gov/factsheets/list-all/.
Herbal Database: memorial Sloan Kettering Cancer Center. https://www.mskcc.org/cancer-care/diagnosis-treatment/symptom-management/integrative-medicine/herbs.
Herbs at a Glance: uS NIH National Center for Complementary and Integrative Health (NCCIH). https://www.nccih.nih.gov/health/herbsataglance.
FoodData Central: searchable nutrient database — US Department of Agriculture (USDA). https://fdc.nal.usda.gov/.
Chapter 14 of 14
Sources (continued)
The Nutrition Source: harvard T.H. Chan School of Public Health. https://www.hsph.harvard.edu/nutritionsource/.
PubMed — peer-reviewed biomedical literature — US National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/