Is spinach more nutritious raw or cooked?

Is spinach more nutritious raw or cooked?

Cooked! Cooking your vegetables can actually boost their antioxidant content. Heating vegetables releases antioxidants by breaking down cell walls. Studies have found that eating cooked spinach and carrots - versus raw - results in much higher blood levels of beta-carotene, an antioxidant thought to guard against heart disease and lung cancer.

You'll also get more lutein, a phytochemical that helps prevent cataract and macular degeneration, if you eat your spinach cooked instead of raw.

And when it comes to certain minerals, you're better off eating your spinach cooked. Green vegetables such as spinach, beet greens and Swiss chard are high in calcium, but their high levels of a compound called oxalic acid binds calcium and reduce its absorption. Cooking releases some of the calcium that's bound to oxalic acid. Three cups of raw spinach, for example, have 90 milligrams of calcium, whereas one cup of cooked has nearly triple the amount (259 milligrams). Cooking vegetables also increases the amount of magnesium and iron that's available to the body.

But water is your enemy when it comes to cooking veggies. Boiling vegetables causes a significant amount of nutrients that dissolve in water - vitamin C, folate and thiamin (vitamin B1) - to be leached away. Steaming is much gentler on nutrients because vegetables don't come in contact with cooking water. Dry cooking methods like grilling, roasting, stir-frying and microwave cooking without water also preserve a greater amount of nutrients than boiling or pressure cooking.

That said, some vegetables are healthier when eaten raw. Cruciferous vegetables such as cabbage, broccoli, cauliflower, bok choy and kale contain glucosinolates that are converted to anti-cancer compounds called isothiocyanates.

An enzyme in cruciferous vegetables converts glucosinolates to isothiocyanates when they're chopped or chewed. But this enzyme is easily destroyed by heat. That means that heating cruciferous vegetables reduces the conversion of glucosinolates to their active isothiocyanates, which may reduce their cancer-fighting potential. You will preserve more phytochemicals in these vegetables if you steam them rather than boil or microwave.

Send dietitian Leslie Beck your questions at dietitian@globeandmail.com. She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

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