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Microwave cooking and nutrition

The Family Health Guide


Almost every American home has a microwave oven. The convenience they offer is undeniable. But despite the widespread use of microwave ovens

and their excellent safety record, some people have lingering doubts that cooking food with microwaves somehow makes food less healthy by zapping away nutrients.

Does cooking with microwaves do that?


Understanding how microwave ovens work can help clarify the answer to this common question. Microwave ovens cook food using waves of energy that are similar
to radio waves but shorter. These waves are remarkably selective, primarily affecting water and other molecules that are electrically asymmetrical — one end
positively charged and the other negatively charged. Microwaves cause these molecules to vibrate and quickly build up thermal (heat) energy.
Some nutrients break down when they’re exposed to heat, whether it is from a microwave or a regular oven. Vitamin C is perhaps the clearest example.
But because microwave cooking times are shorter, cooking with a microwave does a better job of preserving vitamin C and other nutrients that break
down when heated.
As far as vegetables go, cooking them in water robs them of some of their nutritional value because the nutrients leach out into the cooking water.
For example, boiled broccoli loses glucosinolate, the sulfur-containing compound that may give the vegetable its cancer-fighting properties
(as well as the taste that many find distinctive and some find disgusting). Is steaming vegetables better? In some respects, yes.
For example, steamed broccoli holds on to more glucosinolate than boiled or fried broccoli.
The cooking method that best retains nutrients is one that cooks quickly, heats food for the shortest amount of time, and uses as little liquid as possible.
Microwaving meets those criteria. Using the microwave with a small amount of water essentially steams food from the inside out.
That keeps more vitamins and minerals than almost any other cooking method.
But 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.
Microwaving food in plastic: Dangerous or not?
Chances are good that you’ve at some point received an urgent “PLEASE READ THIS!” email about the dangers of microwaving food in plastic containers or plastic
wrap, or run across an article about it on a website. The message is that chemicals leaching out of the plastic and into the food will cause cancer, reproductive problems,
and other ills. Is there any truth to this, or is it just another Internet-fuelled “urban legend”? As is often the case with such warnings, this one contains a small kernel of truth
— and a lot of misinformation.
Let’s cover the original misinformation first: The earliest missives warned that microwaved plastic releases cancer-causing chemicals called dioxins into food.
The problem with that warning is that plastics don’t contain dioxins. They are created when garbage, plastics, metals, wood, and other materials are burned.
As long as you don’t burn your food in a microwave, you aren’t exposing yourself to dioxins.
Migrating chemicals
There’s no single substance called “plastic.” That term covers many materials made from an array of organic and inorganic compounds. Substances are often added
to plastic to help shape or stabilise it. Two of these plasticizers are
bisphenol-A (BPA), added to make clear, hard plastic
phthalates, added to make plastic soft and flexible
BPA and phthalates are believed to be “endocrine disruptors.” These are substances that mimic human hormones, and not for the good.
When food is wrapped in plastic or placed in a plastic container and microwaved, BPA and phthalates may leak into the food. Any migration is likely to be greater
with fatty foods such as meats and cheeses than with other foods.
The FDA long ago recognised the potential for small amounts of plasticizers to migrate into food. So it closely regulates plastic containers and materials that come
into contact with food. The FDA requires manufacturers to test these containers using tests that meet FDA standards and specifications. It then reviews test data
before approving a container for microwave use.
Some of these tests measure the migration of chemicals at temperatures that the container or wrap is likely to encounter during ordinary use.
For microwave approval, the agency estimates the ratio of plastic surface area to food, how long the container is likely to be in the microwave, how often a person
is likely to eat from the container, and how hot the food can be expected to get during microwaving. The scientists also measure the chemicals that leach into food
and the extent to which they migrate in different kinds of foods. The maximum allowable amount is 100–1,000 times less per pound of body weight than the amount
shown to harm laboratory animals over a lifetime of use. Only containers that pass this test can display a microwave-safe icon, the words “microwave safe,”
or words to the effect that they’re approved for use in microwave ovens.
When Good Housekeeping microwaved food in 31 plastic containers, lids, and wraps, it found that almost none of the food contained plastic additives.
What about containers without a microwave-safe label? They aren’t necessarily unsafe; the FDA simply hasn’t determined whether it is or not.
Is Styrofoam microwave safe?
Contrary to popular belief, some Styrofoam and other polystyrene containers can safely be used in the microwave. Just follow the same rule you follow for other
plastic containers: Check the label.
The bottom line
Here are some things to keep in mind when using the microwave:
If you’re concerned about plastic wraps or containers in the microwave, transfer food to glass or ceramic containers labeled for use in microwave ovens.
Don’t let plastic wrap touch food during microwaving because it may melt. Wax paper, kitchen parchment paper, white paper towels, or a domed container
that fits over a plate or bowl are better alternatives.
Most take-out containers, water bottles, and plastic tubs or jars made to hold margarine, yogurt, whipped topping, and foods such as cream cheese, mayonnaise,
and mustard are not microwave-safe.
Microwavable take-out dinner trays are formulated for one-time use only and will say so on the package.
Old, scratched, or cracked containers, or those that have been microwaved many times, may leach out more plasticizers.
Don’t microwave plastic storage bags or plastic bags from the grocery store.
Before microwaving food, be sure to vent the container: leave the lid ajar, or lift the edge of the cover.
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Not taking the chance we never use plastics in the microwave. Ours is mainly for reheating coffee as we don't like the way food will usually taste when heated in the microwave.

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