HOW you serve spinach affects its health-giving properties in surprising ways.
RAW
FRESH spinach is a rich source of vitamin K which promotes bone health, as well as calcium, vitamin D, fibre, potassium (a 90g serving contains more potassium than a banana), magnesium and vitamin C. It also provides beta carotene, zeaxanthin, lutein and chlorophyll, needed for good eyesight and immunity.
Lutein levels are higher in raw spinach, followed by frozen and canned, according to a 2008 study by University College Cork - but the nutrients are depleted if spinach is left to languish on a supermarket shelf or in your fridge.
A study in the Journal of Food Science found that spinach in a fridge loses its folate and carotenoid content at a slower rate than when left out of the fridge. After eight days, much of its nutrients will be lost.
But you need to add fat to your spinach salad or smoothie to absorb its fat-soluble vitamins A, D, E and K.
A study in the American Journal of Clinical Nutrition found that using a fat-free dressing on raw leaf salads significantly reduced absorption of vitamins A and K compared with a full-fat dressing or adding slices of avocado.
Spinach is a good source of iron, but dress your spinach salad with lemon juice. The vitamin C in the juice increases the uptake of iron by up to three times, according to a study in the American Journal of Clinical Nutrition.
Dr Sarah Schenker, a dietitian based in London, warns against over-consuming fresh spinach by stuffing handfuls into a 'green' smoothie.
"Blending spinach allows you to consume greater quantities than you might in a salad, but this could lead to a build-up of chemical oxalate, which can cause kidney stones and which also blocks the absorption of other nutrients," she says.
Opt for baby leaves. Research has shown that these have more polyphenols (health-giving plant compounds).
In a 2017 study, Stephen Fry, a professor of plant biochemistry at Edinburgh University, found that the vitamin C content was higher in baby spinach, and that it seemed to be better able to hang on to nutrients.
Don't wash leaves too vigorously, either. Professor Fry said: "Our experiments showed that the mechanical stress experienced by spinach leaves during washing led to a significant loss of ascorbate [vitamin C], whereas mere submersion did not affect the ascorbate content."
FROZEN
AS frozen vegetables are picked when nutrient levels are at their highest and frozen rapidly, nutrients which might be lost as it sits in the supermarket tend to be preserved for longer.
A study in the journal Food Chemistry found that fresh spinach loses 75 per cent of its vitamin C within seven days of harvest. But the blanching process (where spinach is dipped in boiling water to destroy bacteria before it is frozen) means frozen spinach loses 61 per cent of its vitamin C. Reduce further losses by cooking it unthawed.
COOKED
COOKING spinach reduces its volume to less than 10 per cent. Size for size, one portion of cooked frozen or canned spinach has roughly four times the amount of fibre, folate, iron and calcium as a portion of raw, says Dr Schenker.
Plant foods such as spinach also provide 'non-haem iron', which the body can struggle to absorb efficiently, as the oxalic acid in fresh spinach binds with the iron, blocking its absorption.
But boiling spinach reduces oxalates by up to 87 per cent, according to a 2011 study in the International Journal of Food Properties.
© Daily Mail
