Spinach

Spinach is one of the most nutrient-dense leaves available — a cup of raw spinach provides substantial vitamin K (over 100% RDI), vitamin A, folate, magnesium, and iron, all under 10 calories. It's a frequent component of Mediterranean-style eating patterns associated with cardiovascular and cognitive benefits.

Oxalates and stones

Spinach is among the highest-oxalate foods commonly eaten — substantially higher than almonds, beets, or Swiss chard. For people with a history of calcium-oxalate kidney stones, that's a strong reason to limit spinach and pair what they do eat with a calcium source (dairy, calcium-fortified plant milk). The calcium binds oxalate in the gut, reducing absorption. For everyone else, oxalate is not a practical concern.

Iron and the bioavailability myth

Spinach is often cited as a top iron source — and on a per-weight basis, that's true. But the iron in spinach is non-heme (plant form) and the same oxalates that bind calcium also bind iron, reducing absorption substantially. Pairing spinach with vitamin C (lemon juice, bell pepper, tomato) at the same meal increases iron absorption several-fold. For someone correcting an iron deficiency, animal sources (red meat, organ meats) or supplementation move biomarkers faster than spinach alone.

Cooking spinach reduces oxalate content modestly (some leaches into the cooking water — discard it for kidney-stone formers). The volume also collapses dramatically — a pound of raw spinach cooks down to about a cup — which is why a single recipe portion can deliver substantially more oxalate than a salad does.