Chances are, you've read a sensational story or circulated a chain email about how microwaves zap nutrients from food.
As it turns out, though, microwaving may be the best way to keep more nutrients in your vegies than other cooking methods, according to experts. Why care? Because many of us are overcooking our vegies and losing key nutrients as a result, according to a new survey.
America's National Brassica Survey found that most people cook broccoli for 10 minutes or longer, a length of time that destroys the vegie's rich stores of a detoxifying nutrient called glucoraphanin. To keep this powerful compound intact, the report says, we should cook broccoli for just 3 to 5 minutes. The takeaway: broccoli, like most veggies, keeps more nutrients when it's cooked for the shortest amount of time possible. And how can you cook crisp-tender broccoli in just 3 minutes? You guessed it: the microwave.
Unlike a regular oven, which heats the air around food, a microwave heats the molecules of the food itself. It produces microwaves, a type of electromagnetic radiation that passes right through materials like glass and plastic, but is absorbed by the water molecules in food. These waves cause those water molecules to vibrate, which creates heat in a shorter amount of time, helping to keep nutrients intact.
Microwaves also cook food at relatively low temps and without a large amount of water, both which also preserve nutrients since high temps can slash nutrients while water can leach them. Take, for example, a potato, which is a good source of vitamin C. If you boil it, vitamin C would leach into the cooking water. If you roast it for a half hour at 200C, the high oven temp and long cooking time would also degrade vitamin C, which is sensitive to heat. But if you stab it a few times with a fork and pop it in the microwave, just a few minutes later, it'll be cooked through and ready to eat without ever touching water.
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Though there are a few exceptions (nutrients like lycopene, beta-carotene, and some polyphenols actually become more bioavailable when cooked), a quick turn in the microwave is hard to beat. In fact, a recent Harvard Medical School report plainly states that microwaving "keeps more vitamins and minerals than almost any other cooking method."
That said, just about every expert agrees that, as long as you're eating a balanced diet with lots of veggies, there's no need to split hairs over cooking methods. "Selecting a variety of nutrient-dense foods is the most important thing you can do," says Bradley Bolling, a food scientist at University of Wisconsin-Madison.