The Free Press, Mankato, MN

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April 22, 2014

Dietitian: Nutrient-loss in microwave myth is a little overcooked

Q: Is it OK to use my microwave to cook vegetables? Someone said microwaves destroy almost all the nutrients in the food, versus steaming on the top of the stove where the loss is minimal. I usually only use the microwave to defrost or reheat, but am I reducing the food value?

A: Almost every American home has one. The convenience offered by owning a microwave oven is nearly undeniable. Microwaves are wonderful in that they can heat foods quickly, which is a must for time-strapped families. But there remains a level of skepticism for many — a lingering feeling that using a microwave to cook food may somehow make food less healthy.

There are three factors that affect nutrient loss when you cook vegetables: temperature, time and water. Nutrients tend to be both heat-intolerant and water-soluble. This means that any method that requires cooking at a high temperature for a long time and uses a lot of water will result in the greatest nutrient loss. (So by this measure, boiling vegetables is likely the worst offender.) It goes without saying then that cooking at a lower temperature for a shorter amount of time and with less water would result in the least amount of nutrients lost, and that's what the microwave accomplishes.

So where did this idea originate in the first place? A 2003 study in the Journal of the Science of Food and Agriculture claimed that steaming broccoli in the microwave caused it to lose 97 percent of its antioxidants, while stovetop cooking only resulted in an 11 percent loss. But if you read all the details, you will see that the study used more water than would ever be necessary in a microwave, and thus the results are flawed and not realistic.

Cooking can actually increase our body’s ability to use certain nutrients. The lycopene in tomatoes and the carotenoids in carrots are both better absorbed after a quick heat. So let’s not get too lost in the details. Vegetables, pretty much any way you prepare them, are good for you, and most of us don’t eat enough of them. And the microwave oven? A marvel of engineering, a miracle of convenience — and sometimes nutritionally advantageous to boot.

April Graff, MS, RD, LD, is a reg­istered dietitian at both Mankato Hy-Vee stores and can be reached at AGraff@hy-vee.com or call 625-1107 or 625-9070. Send her ques­tions about food and nutrition, recipes, meal planning and healthy shopping.

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