Microwave ovens - what great conveniences! We seem to be accustomed to their place in our kitchens. But how many of us even know anything about them? Who invented the microwave? How do they work their cooking magic? And, perhaps most important, how do they affect the food we eat?
A Brief History of the Microwave
Like many other inventions, the microwave was a by-product of another technology. In 1946, Dr. Percy Spencer, a self-taught engineer with the Raytheon Corporation, was working on a radar-related research project. He was testing a new vacuum tube called a magnetron when he discovered that the candy bar in his pocket had melted. The puzzled Dr. Spencer tried another experiment. This time he placed some popcorn kernels near the tube and, perhaps standing a little farther away, he watched as the popcorn sputtered, cracked and popped all over his lab. He repeated the experiment with an egg and discovered it also cooked.
Believing these occurrences may have some commercial use, Percy Spencer and an associate, P.R. Hanson began working on this project they called "the Speedy Weenie." The "Speedy Weenie" Project was the nickname Spencer and Hanson gave to their secret project, the microwave oven. "'Speedie Weenie" meaning "a quick hot dog!"
Eventually, Dr. Spencer fashioned a metal box with an opening into which he fed microwave power. The energy entering the box was unable to escape, thereby creating a higher density electromagnetic field. When food was placed in the box and microwave energy fed in, the temperature of the food rose very rapidly. Dr. Spencer had invented what was to revolutionize cooking, and form the basis of a multimillion dollar industry, the microwave oven. (John Carlton Gallawa, "Microwave Oven," World Book Encyclopedia)
In 1947, the first commercial microwave oven hit the market -- gigantic and enormously expensive primitive units, standing 5 1/2 feet tall, weighing over 750 pounds, and costing about $5000 each. The magnetron tube had to be water-cooled, so plumbing installations were also required. The rest of the story is evident.
How Microwaves Cook
Microwaves have three characteristics that allow them to be used in cooking: they are reflected by metal; they pass through glass, paper, plastic, and similar materials; and they are absorbed by foods.
Microwaves are produced inside the oven by an electron tube (magnetron); then, they are reflected within the metal interior of the oven where they are absorbed by food. Microwaves cause water molecules in food to vibrate, producing heat that cooks the food, so 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."
Although heat is produced directly in the food, microwave ovens do not cook food from the "inside out." When thick foods are cooked, the outer layers are heated and cooked primarily by microwaves while the inside is cooked mainly by the conduction of heat from the hot outer layers.
Is Microwave Cooking Safe?
Trudy Bialic, editor of www.pccnaturalmarkets.com ("Microwaved Food: Is It Healthy?" January 2006) reported, "The U.S. Food and Drug Administration (FDA) has regulated the manufacture of microwave ovens since 1971 and has authority over food safety. But a review of 200 references on its Web site reflects more attention to potential radiation leakage than the effects of eating microwaved foods. The only reference to food quality that I found says, 'foods cooked in a microwave oven may keep more of their vitamins and minerals because microwave ovens can cook more quickly and without adding water.'”
The FDA does recommend that microwave ovens not be used in home canning since neither microwave ovens nor conventional ovens produce or maintain temperatures high enough to kill the harmful bacteria that occur in some foods while canning.
One long-time microwave cooking concern has been leakage from containers. According to the Harvard Family Health Guide, "When food is wrapped in plastic or placed in a plastic container and microwaved, substances used in manufacturing the plastic (plasticizers) may leak into the food. In particular, fatty foods such as meats and cheeses cause a chemical called diethylhexyl adipate to leach out of the plastic." But, the FDA requires that manufacturers test these containers and that those tests meet FDA standards and specifications.
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.
What about containers without a microwave-safe label? Only those containers labeled “microwave safe” have been tested and found safe for that purpose. A container that’s not labeled safe for microwave use isn’t necessarily unsafe; the FDA merely simply hasn’t determined whether it is or not. ("Microwaving Food In Plastic" Dangerous Or Not?" Harvard Medical School Family Health Guide, www.health.harvard.edu, 2006)
Most investigations concluded microwave cooking, if properly done, does not change the nutrient content of foods to a larger extent than conventional heating. In fact, many studies suggests there is a tendency towards greater retention of many micronutrients with microwaving, probably due to the shorter preparation time.
(C.Anne Lassen, Lars Ovesen, "Nutritional effects of microwave cooking", Nutrition & Food Science, Vol. 95 Iss: 4, 1995)
Dr. Sanjay Gupta, neurosurgeon and correspondent for CNN and CBS, proposed the inevitable fact that no matter how food is cooked, whether it’s steamed, boiled, microwaved, or cooked in a toaster oven, any type of cooking will destroy some nutrients in foods. The key, according to the U.S. Department of Agriculture, is to prevent excessive losses of vitamins and minerals by using proper preparation and cooking techniques. Gupta believes microwave cooking exposes most foods to less heat, water, and for shorter cooking periods, so that means that fewer vitamins will be destroyed during cooking. ("Does Microwave Cooking Rob Food of Nutrients?" The Chart, CNN Health, July 1 2010)
Dr. Swamy Anantheswaran, associate professor of food science in Penn State's College of Agricultural Sciences, said, "Total cooking time can be much less, allowing for greater retention of nutrients. However, most consumers manage to overcook their food by leaving it in the microwave too long or by using too high of a power setting." The solution is simple, he says, and as important for safety as for good eating. "Use the appropriate power setting for the food you're microwaving," reminds Anantheswaran, "and make sure you read the manual!" ("How Do Microwaves Cook Food?" Research Penn State, November 28 2005)
However, certain non-thermal effects do occur. The main problem with microwaving is the uneven heating of the food, which has raised concern regarding microbiological safety. Microwaving infant formula and breast milk has become increasingly popular. The content of nutrients and antibacterial factors in milk are maintained unchanged provided the final temperature does not exceed 60°. To help preserve nutrients when microwaving food, people should use techniques that promote the even distribution of heat. This will help prevent the formation of "hot spots" where portions of the food could be over-cooked.
D.L. Hentges ("Keeping Food Safe For Baby," National Network for Child Care, 1995) also recommended removing baby bottle caps or nipples before warming baby formula in a microwave since the outer container (or baby bottle) may feel cool to the touch even though the formula inside is very hot. It is important not to heat microwave disposable baby bottles or bottles with disposable plastic inserts. Heating milk in these bottles may cause hot spots. Microwave heating may weaken the seams causing the plastic to burst and spill hot milk on the baby.
But, Some Have Reported Major Concerns
Skepticism about the safety of microwave cooking does exist. Since 1957, the Russians have performed extensive experiments with microwave ovens at the Institute of Radio Technology. Early research suggested people who ingested microwaved foods showed a statistically higher incidence of stomach and intestinal cancers. This was believed to result from malfunctions in the lymphatic system and impairment of the immune system's capacity to protect the body against neoplastic (cancerous) growth. As a result of these findings, microwave ovens were banned in Russia in 1976; however, the ban was lifted years later under new leadership. (Kashish Gupta, "Microwaved," November 2003)
Two notable figures in the study of microwaved foods are Dr. Hans Hertel and Bernard H. Blanc, whose Swiss research concluded that after eating microwaved food, hemoglobin levels decrease, cholesterol increases, white blood cell count increases, red blood cell count decreases and radiolytic compounds (unknown in nature) are produced in the blood.
Dr. Hertel was the first scientist to conceive and carry out a quality clinical study on the effects microwaved nutrients have on the blood and physiology of the human body. His small but well controlled study (1991) showed the degenerative force produced in microwave ovens and the food processed in them. The scientific conclusion showed that microwave cooking changed the nutrients in the food; and, changes took place in the participants' blood that could cause deterioration in the human system.
The significant changes in the participants' blood samples after eating microwaved food included reduced hemoglobin and cholesterol values, especially the ratio of good vs. bad cholesterol. White blood cells for immune function showed a distinct short-term decrease. Hertel also found irregularities in the structure of the microwaved food — the creation of new compounds called “radiolytic” compounds that are unknown in nature. (Stephanie Relfe, "Microwave Cooking Is Killing People!" www.relfe.com/microwave)
There was a highly significant association between the amount of microwave energy in the test foods and the luminous power of luminescent bacteria exposed to serum from test persons who ate that food. This led Dr. Hertel to the conclusion that such technically derived energies may, indeed, be passed along to man inductively via eating microwaved food. ("Radiation Ovens: The Proven Dangers of Microwaves," Health Freedom Resources Public Awareness Announcement #1, June 12 2000)
Other Findings Of Interest
As early as 1989, the Lancet British medical journal reported that heating baby formula in a microwave changed its chemistry. Dr. Lita Lee found that microwaving converts some trans-amino acids into synthetic substances similar to unhealthy trans-fatty acids; one amino acid, L-proline, reportedly converted to a substance that’s reputed to be toxic to the nervous system and kidneys. (Gary Alexander, "Throw It In the Microwave," Chronogram, February 2001)
A group of scientists at the Stanford University School of Medicine in California (1992) discovered that microwaving breast milk at high temperatures (72°C to 98°C) caused a marked decrease in activity of all the tested anti-infective factors. E. coli growth at >98°C was 18 times that of control human milk. Even at 20°C to 25°C, E. coli growth was 5 times that of control human milk. Because microwave radiation leads to a significant loss of the immunological properties of milk, the authors of the study concluded that microwaving is definitely "not a suitable heat treatment modality for breast milk". (R. Quan et al, "Effects of Microwave Radiation On Anti-Infective Factors in Human Milk," Pediatrics, 89, 1992)
Japanese research reported in Science News in 1998 said microwaving destroys vitamin B-12. Six minutes of microwave cooking destroyed half the B-12 in meat and dairy, a much higher rate than from conventional cooking. This may be due to excessive overcooking. (Janet Raloff, "Academic Impacts of Vegetarian Childhoods," Science News)
A Spanish study by the Spanish Scientific Research Council (CEBAS-CSIC) published in the Journal of the Science of Food and Agriculture in 2003 found that microwave cooking destroys at least some important nutrients in vegetables. Microwaved broccoli lost 97 percent, 74 percent and 87 percent of three cancer-protecting antioxidants (flavonoids, sinapics and caffeoyl-quinic derivatives). Steamed broccoli lost 11 percent, 0 percent and 8 percent of these compounds.
The Biggest Microwave Concern - Obesity?
We know, of course, many children are spending less time exercising and more time in front of the TV, computer, or video-game console. And today's busy families have fewer free moments to prepare nutritious, home-cooked meals. From fast food to electronics, quick and easy is the reality for many people in the new millennium.
The BBC News ("Did Microwaves 'Spark' Obesity?" June 6 2007) reported, "Professor Jane Wardle says obesity rates started to rise soon after 1984 - around the time of the rapid spread of microwave ownership. In 1980, 8% of women and 6% of men were classified as obese. By 2004 this had increased to 24% of men and women....Professor Wardle who is professor of clinical psychology at University College London said: 'I looked at the figures showing rates of obesity in the population over many years and it seem very clear it began between 1984 and 1987. So then we looked at what changes were going on in the food and activity world at that time and one of the striking changes was there were differences in the speed with which we could prepare a meal as a consequence of the introduction of microwaves."
Were microwave ovens a huge trigger for obesity? According to the BBC, in 1980, 8% of women and 6% of men were classified as obese. By 2004 this had increased to 24% of men and women. Children are also suffering from increased levels of obesity, with 16% of children aged two to 15 classed as obese in 2003 compared with 10-12% in 1995. One of the striking changes in eating in the period was the speed with which people could prepare a meal as a consequence of the introduction of microwaves.
One startling look at obesity also has suggested another culprit. Back to the old plastic controversy. Jennifer Lee reported, "Exposure to chemicals used in plastics may be linked with childhood obesity, according to results from a long-term health study by researchers at Mount Sinai Medical Center on girls who live in East Harlem and surrounding communities." ("Child Obesity Is Linked To Chemicals In Plastic," The New York Times, April 17 2009)
The chemicals in question are called phthalates, which are used to to make plastics pliable and in personal care products. Phthalates, which are absorbed into the body, are a type of endocrine disruptor — chemicals that affect glands and hormones that regulate many bodily functions. They have raised concerns as possible carcinogens for more than a decade, but attention over their role in obesity is relatively recent.
About 40 percent of the children in East Harlem are considered either overweight or obese. “When we say children, I’m talking about kindergarten children. We are talking about little kids,” Dr. Philip J. Landrigana, professor of pediatrics at Mount Sinai, one of the lead researchers on the study said. “This is a problem that begins early in life.”
The Story of Percy Spencer's Microwave Oven On Video