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Ask Tufts Experts December 2012 Issue

Q: Is it true that heating food in a microwave oven destroys most of the nutrients while creating byproducts that affect your brain and hormones?

Answer :  In fact, says Irwin H. Rosenberg, MD, editor of the Tufts Health & Nutrition Letter, the opposite is true: "Foods cooked in a microwave oven may keep more of their vitamins and minerals, because microwaves can cook food more quickly and without adding water—nor do you have to add fat. At worst, microwave cooking reduces nutrient levels in food no more than conventional cooking."

As for supposed dangerous byproducts from microwave cooking, this is an urban legend spread by the Internet. The US Food and Drug Administration says cooking with microwaves is safe: “Microwaves cause water molecules in food to vibrate, producing heat that cooks the food. That’s why foods high in water content, like fresh vegetables, can be cooked more quickly than other foods. The microwave energy is changed to heat as it is absorbed by food, and does not make food ‘radioactive’ or ‘contaminated.’"

The chief caution about microwave cooking concerns the containers you use in the microwave oven. The FDA warns, “Some plastic containers should not be used in a microwave oven because they can be melted by the heat of the food inside. Generally, metal pans or aluminum foil should also not be used in a microwave oven, as the microwaves are reflected off these materials causing the food to cook unevenly and possibly damaging the oven."

Microwave ovens should not be used in home canning, because they don’t produce or maintain temperatures high enough to kill the harmful bacteria that occur in some foods while canning. Similarly, frozen foods cooked in the microwave must be carefully prepared according to manufacturers’ directions, to make sure raw ingredients are thoroughly cooked.

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