Iron, magnesium and folate in green vegetables

What these nutrients are recognised for

Dark leafy greens are a genuine dietary source of all three, and each has recognised functions on the UK nutrition and health claims register. In the register's own words:

Iron contributes to normal formation of red blood cells and haemoglobin, to normal cognitive function and to the reduction of tiredness and fatigue.

Magnesium contributes to normal muscle function, to normal functioning of the nervous system and to the maintenance of normal bones.

Folate contributes to normal blood formation, to normal amino acid synthesis and to the reduction of tiredness and fatigue.

That is why greens keep coming up whenever tiredness, muscles, bones or blood enter the conversation. The nutrients are real, they are in the leaves, and these are the functions the evidence supports.

Where each one sits in a green vegetable

Iron is present across dark leafy greens, spinach and kale included. The important caveat is form: plant iron (non-haem) is absorbed less readily than the iron in meat, and its absorption is affected by what's eaten alongside it. Vitamin C in the same meal helps, which is a tidy accident of green juice recipes, since lemon turns up in most of them.

Magnesium sits at the centre of the chlorophyll molecule itself, which is a genuinely satisfying fact: the thing that makes greens green is built around it. Leafy greens are consequently a reasonable dietary source.

Folate takes its name from folium, Latin for leaf, which tells you where it was first found. Dark leafy greens, spinach especially, are among its notable sources.

The spinach and oxalate footnote

Spinach's iron reputation is partly overstated, and the usual explanation for why is itself a bit of a myth. The story most people have heard goes like this: back in the 1870s a scientist measured spinach's iron and slipped a decimal point, writing it as ten times higher than it really was, and that inflated number stuck around for decades, inspiring Popeye along the way. It's a great story. The catch is that historians have gone looking for that misplaced decimal and never found it, so the tidy "one scientist fumbled a typo" origin is really an urban legend about an urban legend.

The real reason is duller but more useful: oxalates. Spinach is high in them, and oxalates bind minerals including iron and calcium, which reduces how much your body actually absorbs. Spinach is still a perfectly good vegetable, it just isn't the iron powerhouse the cartoon implied. Kale, which is lower in oxalates, is the more efficient leaf on that particular measure.

What juicing changes

Juicing leaves the insoluble fibre in the pulp and presses the water-soluble content into the juice, so minerals and water-soluble vitamins largely come through. Cold-pressing does it without heat, which matters for the heat-sensitive end of the list, folate among them. What juicing mainly does, though, is concentrate: a bottle represents considerably more leaf than you'd eat in a sitting, which is the practical argument for a vegetable-only green juice alongside eating your greens rather than instead of them.

The wider context for these nutrients lives on our energy, focus and bone health pages, and the vegetable-by-vegetable breakdown is in what each green contributes.

The greens these come from

If you want the leafiest of the range, where the dark greens are most concentrated:

The bottom line

Iron, magnesium and folate are all genuinely present in dark leafy greens, and the register recognises real functions for each: red blood cell formation, muscle and nervous system function, bones, blood and the reduction of tiredness and fatigue. The one honest nuance worth keeping is form, plant iron is absorbed a little less readily than meat iron, though the vitamin C from lemon helps, and cold-pressing brings the water-soluble nutrients through without heat. The vegetable-by-vegetable version is in what each green contributes.