Which cooking method is best for retaining nutrients in broccoli?
1. Boiling broccoli in a pot of water on a stove?
2. Heating broccoli in covered glass bowl in a microwave?
What’s best for your health?
1. Frying bacon in a steel skillet?
2. Cooking bacon in a microwave?
Which method is more energy efficient?
1. Heating up leftovers in a covered container in the oven?
2. Heating up leftovers in a covered glass bowl in the microwave?
Most consumers do not know how microwaves work. Only a few recall that the technology was discovered in 1945 by a self-taught engineer employed by Raytheon. Percy L. Spencer was walking through a radar test room with a chocolate bar in his pocket when he came too close to a running magnetron tube. It melted the candy bar in his pocket and he took notice.
Spencer, a remarkable individual who was famous for his curiosity and ingenuity, decided to see if he could actually cook something with a magnetron tube. So he pointed the magnetron at kernels of corn. They popped! He aimed it at an egg which cooked so fast it exploded. Soon after microwave meals were being served in Raytheon’s executive dining room. Two years later Raytheon was marketing a commercial “Radarange” for $2,000 to $5,000. ($100 in 2019 has the same purchasing power as $10 in 1950.)
But the question remains, did this remarkable individual unleash a plague on all humanity?
This question has been asked and answered many times in the scientific literature. Foods have been cooked by every fashion and analyzed for nutrient degradation or, in some rare cases, enhancement. True to form, most people have not reviewed the studies and have often been using the worst cooking methods for nutrient retention.
Some people have a natural tendency to fear or doubt new technology and that includes microwave ovens. I could list scores of other examples dealing with farming, ranching, food, diets, nutrition, and cooking. Certainty, over the ages some new ideas have not panned out. Even in today’s medical profession there are common practices that grew out of “logical” theories which were never properly tested. For example, eating low fat foods was assumed to be a good way to lose weight. Yet modern studies comparing low-fat diets to high-fat diets do not support the old theory. The same holds true for old theories about avoiding saturated fats in the diet and lowering cholesterol levels to prevent chronic heart disease.
In 2009 a study titled “Influence of Cooking Methods on Antioxidant Activity of Vegetables” compared how boiling, microwaving, pressure cooking, griddling, frying, and baking influenced antioxidant activity of 20 vegetables. Artichokes did the best in all cooking methods. The highest losses were observed in boiling cauliflower in water on a stove and in a microwave, peas after boiling, and zucchini after boiling and frying. Griddling, microwave cooking, and baking alternately produced the lowest losses, pressure cooking and boiling the greatest losses, and frying was in the middle. A big reason for some differences was caused by cooking with water. It’s not the cook’s best friend when it comes to cooking vegetables and retaining their nutrients.
Microwave ovens work because the “electromagnetic” radiation they produce is reflected by the metal sides of the box yet can pass through glass, paper, plastic, and similar materials. Importantly the radiated microwaves are absorbed by foods (especially water) causing water molecules in food to vibrate, producing heat that cooks the food. This molecular agitation from within the food heats it just like molecular agitation from a hot oven or hot skillet transfers its higher temperature to the food from the outside to the inside. All forms of cooking depend on molecular agitation. Naturally, no cooking method utilizing molecular agitation will make food “radioactive” or “contaminated.”
Many of us assume microwave ovens cook food from the “inside out.” But when thick foods are cooked, the outer layers are heated first and the inside is cooked mainly by the conduction of heat from the hot outer layers, just like with all other cooking methods.
Fears are commonplace regarding the electromagnetic radiation generated by microwaves. Visible light, microwaves, and radio frequency radiation are forms of non-ionizing radiation which do not have enough energy to knock electrons out of atoms. But of course when overexposed, even microwaves can be a problem. So when using microwaves one needs to exhibit some common sense and know how to safely use them just like knowing how to safely operate any piece of equipment.
Electromagnetic radiation is reflected by metal, therefore microwave ovens are steel boxes. Even the window in the door is covered by a steel screen. Since the strength of the radiation drops dramatically with distance, the FDA states that a distance of two inches from the box is safe. Standing back several feet from an operating microwave oven provides even a far higher degree of safety.
All cooking methods cause some loss of nutrients. Catherine Adams Hutt, RD, Ph.D. a registered dietician and certified food scientist says “The best cooking method for retaining nutrients is one that cooks quickly, exposes food to heat for the smallest amount of time, and uses only a minimal amount of liquid.” In addition we know that burning food is carcinogenic. So which cooking method comes out on top? You guessed it, a microwave oven!
Here’s the bottom line that answers the three-part quiz.
A 2003 study in “The Journal of the Science of Food and Agriculture” found that when broccoli is immersed in water and cooked in a microwave it loses nearly all of its antioxidants. The same occurs when it’s boiled in a pot of water. When steamed or cooked in a microwave without water, broccoli retains most of its nutrients. Scientists at Cornell University found that bacon cooked by microwave has significantly lower levels of cancer-causing nitrosamines than conventionally cooked bacon. In terms of efficiency, for most meals a microwave oven uses less energy than an electric oven. The operating time for cooking usually determines the cost. When individual foods are microwaved one at a time the microwave advantage is reduced compared to warming up all the foods together in a conventional oven.
Once again a simple question can result in answers that many would not have anticipated. This microwave story is a good example.
To your health.
Ted Slanker has been reporting on the fundamentals of nutritional research in publications, television and radio appearances, and at conferences since 1999. He condenses complex studies into the basics required for health and well-being. His eBook, The Real Diet of Man, is available online.
Don’t miss these links for additional reading:
Melted Chocolate to Microwave by Technology Review
Percy L. Spencer Inventor of the Microwave from Wikipedia
Magnetrons by Chris Woodford from Explain That Stuff
Influence of Cooking Methods on Antioxidant Activity of Vegetables by A. M. Jiménez-Monreal, et al.
Microwaves and Nutrition by Steven Novella for Science Based Medicine
Do Microwaves Zap Nutrition? by Bob Barnett at WebMD
The Claim: Microwave Ovens Kill Nutrients in Food by Anahad O’Connor in The New York Times
Microwave Oven Radiation from U.S. Food and Drug Administration
Heat Transfer from the Physics Department at Georgia State University
Let it Be Red by Ted Slanker