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Is Microwaved Food Dangerous? The myths and the facts.

Renee Despres
04/05/2011 - 12:48

Is microwaved food really hazardous to your health? Do hidden dangers lurk in the chemical structures of foods cooked in a microwave oven? Type “microwave food dangers” into any web search engine, and you’ll discover a multitude of claims about the supposed hazards of microwave ovens. According to these stories, foods cooked in microwave ovens cause almost every ailment known to humans, from cancer to lowered IQ to heart disease to fatigue.

Oh, What a Tangled Web of Microwave Oven Myths

We have a love-hate relationship with our microwave ovens. About 90 percent of us own one; they’re ubiquitous in restaurants, coffeeshops, airports, even corner convenience stores. But we’re also nervous about those little black (silver, red, grey….) boxes that haunt our kitchen countertops.

Stories detailing the dangers of microwaved food permeate the internet. Yet it takes only a quick skim and a smattering of scientific literacy to see that most of the claims made in those stories are based on poor science, rumors, fear mongering, and conspiracy theory. Some of my personal favorite myths:

  • Microwaved food, when consumed continuously over a long period, “shorts out” electrical impulses in the brain, depolarizing or de-magnetizing brain tissue.
    • Reality check: Search after search of PubMed, the Cochrane Library, and CINAHL turned up no research supporting this claim.
  • Microwaving food changes its chemical composition in some mysterious, unknown way, destroying the “vital energy” and nutrients in food.
    • Reality check: As far as changing the chemical composition of food… um, what happens to it when you bake, broil, sauté, or otherwise apply heat to it? And microwaving food generally preserves more nutrients, mostly because cooking time is shorter and the food can be cooked in less water.
  • Microwaving water cause changes in its “structure or energy.”  This one started out as one of those widely-circulated emails that described somebody’s granddaughter’s science fair experiment. One plant was watered with water that had been boiled on a stovetop, the other with water that had been boiled in the microwave.  The accompanying photos supposedly show the gradual demise of the plant watered with the microwaved water.
    • Reality check: As an experiment, the two-plant scenario wouldn’t pass muster for an elementary school science fair project. Barbara Mikkelson over at Snopes.com offers an explanation of the scientific method – for those of you who slept through junior high science class – and debunks this myth solidly. She also ended up with several very healthy-looking plants.
  • Microwaving food or water causes the formation of "radiolytic compounds" — new chemicals created by the tearing apart of molecules. Depending on the version of the microwave myth, these chemicals are said to be cancerous, radioactive, unnatural, or otherwise dangerous.
    • Reality check: Microwaves do not have enough energy to “tear apart” molecules. Microwaves are simply electromagnetic waves – they have nothing to do with radioactivity.
  • Male and female hormone production is shut down and/or altered by continually eating microwaved foods.
    • Reality check: A search of PubMed, Cochrane, and CINAHL turned up no results in peer-reviewed journals.

If any of these (or several other equally off-the-wall stories) were true, it would be a miracle that anyone is alive, thinking, and reproducing. Consider that microwave ovens have been used for more than 50 years – in our homes, restaurants, laboratories, and more.

No valid, peer-reviewed research has ever documented that microwaving food or water causes any of these ill effects.  

Critical thinking lesson #1: Always question claims that seem too strange and grandiose – especially if they’re presented in pseudoscientific language.

How Do Microwave Ovens Work?

To understand why these claims are so ludicrous, you first need to understand how microwave ovens work. When you push the “Start” button on your microwave oven, tiny, energetic waves start moving through the inside compartment of your oven, passing through everything in the compartment. These waves, called microwaves, are a type of electromagnetic radiation. The waves vibrate rapidly, at about 2,500 megahertz (2.5 gigahertz) a minute. That’s about the same frequency as your cell phone.

A little clarification about the word “radiation” is in order here. Microwaves radiate – just like waves in a pool of water radiate outward if you drop a rock in a pool of water. But they are a type of non-ionizing radiation, unlike potentially harmful ionizing radiation. Ions are charged particles that split off from a molecule. Microwaves and other typed of non-ionizing radiation have enough energy to cause atoms in a molecule to move or vibrate, but not enough to remove particles. Sound waves, visible light, and microwaves fall in this category. Ionizing radiation, however, has enough energy to kick off electrons from atoms – creating ions.  Examples of ionizing radiation include ultraviolet light from the sun, x-rays, and gamma rays.

As those microwaves vibrate, they are absorbed by any water present in the oven. The energy in the waves causes water to vibrate quickly. This is because of a special characteristic of water: it has a positive and negative end (remember your high school chemistry? Hydrogen carries a plus-1 charge, and oxygen a minus-2). In other words, it is a dipole. As the water molecules vibrate, the friction between them creates heat. In turn, the heat cooks the food.

All food contains some water, so when microwaves travel through food, it heats quickly. Most plastics, glass, paper, and ceramics are unaltered by microwaves. Metals, however, reflect microwaves. That’s why metal pans and aluminum foil should not be used in microwave ovens.

Microwaves do not cook food from the inside out (another microwave myth). Microwaves are absorbed in the outer layers of food, in much the same way as in conventional cooking methods. The heat from outer layers of the food actually cooks the innermost areas.

Critical thinking lesson #2: Be sure to include a physics teacher in your circle of friends.

Microwave Mythologists

One of the strongest anti-microwave voices on the web is Joseph Mercola, an Illinois-based alternative physician who runs www.mercola.com. Mercola.com has been recycling and adding to an article about the “proven dangers of microwaves” since at least 1994. By 2010, the Mercola spiel had incorporated just about every microwave myth known to the internet.

Mercola mixes in just enough truth to make it seem believable – for instance, you can kill 99 percent of bacteria on a dish sponge by microwaving it on high for one minute. He cites a few trustworthy sources (such as the Food and Drug Administration) for information about the verified hazards of microwave cooking. But that’s about where the reliability stops. Click around a bit, and you’ll find that most of Mercola’s sources about the hazards of microwaved foods are strongly biased and based on shoddy science.

Mercola, like almost every other writer who expounds the microwave myth, includes the story of the Swiss food chemist Hans Hertel. In the late 1980s, Hertel and seven fellow vegetarians locked themselves into a hotel room, where they performed a two-month “experiment” that consisted of eating foods prepared in the microwave and by other means.

After two months of togetherness, Hertel emerged with a terrifying pronouncement:  He had found changes that “appear to indicate the initial stage of a pathological process such as occurs at the start of a cancerous condition” in the blood of the men who had eaten microwaved milk and vegetables. 

But…

  • None of the men in the study got sick.
  • The study was never published in a peer-reviewed journal.
  • Hertel never produced the data
  • Tthe study has never been replicated.
  • A sample size of four does not provide any significant information. 

Hertel since seems to have disappeared (according to Mercola, a “gag order” from the Swiss government silenced him), but his story is alive and well on the internet.

Critical thinking lesson #3: Valid scientific findings are replicable, documented, and involve more than eight people.

The second “big name” in the microwave mythology story is James Kopp. Little information is available about his credentials – in most places, he is only described as “a U.S. researcher,”  but his word has been taken as gospel by true believers. In a 1996 he published an article about the research  of Russian scientists into microwaves – which supposedly led to banning microwave ovens in Russia. http://www.mindfully.org/Food/Irradiate-Microwave-Effects-FoodMay96.htm.  

 But Kopp disappeared. He changed his name and claimed that microwave oven manufacturers were persecuting him.  .

Critical thinking lesson #4: Ethical, reputable, mentally-healthy scientists stand by their work. They do not change their names and disappear, claiming persecution.

Mercola adapts much of his information from Powerwatch , a strong anti-microwave advocacy group based in the U.K. According to their website, they are “a small non-profit independent organisation with a central role in the UK Electromagnetic Field and Microwave Radiation health debate.”  Their companion organization, EMFields.org, will happily sell you products designed to screen you from the dangers of electromagnetic fields.  A protective sleeping bag will run you about €225 (about $310 US).

Is there a healthier alternative to this fearsome microwave cooking? Certainly, says Mercola. He proposed his turbo oven –which you can purchase  for the incredibly low price of $84.57.

Buy one because his article convinces you that microwaves are killing you, and I’ll lower your critical thinking score to negative 50.

Critical thinking lesson #5: Never trust a source that tries to sell you something.

Another common claim, found not in almost every “microwaved food is dangerous” story,  is that heating human breastmilk in microwave ovens destroys leukocytes, the compounds that give the milk its immune properties. This claim is based on a 1992 study by Richard Quan et al. microwaved 22 samples of freshly frozen human breast milk, some at high power, and some at low. They found that the high power, 18 times infective properties; low power, five times. 

But the researchers did not examine the effects of other types of heat on human breast milk. So the study really showed nothing about microwave, per se, but only about heat on human breast milk.

Numerous, more recent, studies suggest that human breastmilk emerges from a microwave without major alterations. Some of these studies even show a benefit to microwaving human breastmilk, especially in certain geographical regions:

  • A team based in The Netherlands found that “mature human milk can be stored safely in a freezer and heated in a microwave oven without loss of fat or carotenoids.”
  • In 2003, a Brazilian team found that heating milk to a temperature of 63 degrees C (X F) in a microwave can effectively pasteurize the milk and kill T. cruzi trypomastigotes, the organism that causes Chagas disease.
  • In 2002, a pair of Spanish researchers concluded that although microwaving breast milk caused longer coagulation times and slower curd formation, “microwave heating was no more detrimental to the milk than conventional heating and could thus be used for pasteurization purposes.”  

In short, many studies have demonstrated that human breast milk that’s been heated in a microwave oven is… well… human breast milk that’s been heated in a microwave. But microwave mythologists still rely on two 20-year-old studies that were poorly designed.

Critical thinking lesson #5: If a study raises potentially serious concerns about health, other researchers will attempt to replicate it. Studies that are 20 years old have probably been supplanted by newer research.  

The Real Dangers of Microwave Ovens

Are there real hazards associated with microwaving foods? Of course. Any form of cooking can be unsafe – after all, we’re talking about hot food here. But the hazards have nothing to do with the microwaves themselves; with a couple of exceptions, they are the same hazards associated with almost any cooking method. Here are some real, not-hidden hazards of microwave cooking – and their solutions -- identified by the FDA:

Heat. Microwaved food can be very hot, and conventional microwave cooking can heat food unevenly, leading to extremely hot areas in food that might not be heated completely.

  • Avoid using a microwave to heat food for infants and young children. If you must, use extreme caution.
  • Never microwave for longer than the recommended time, and always be sure to stir food thoroughly.
  • Formula or breastmilk that is warmed in a microwave should always be tested for temperature before giving it to an infant.
  • Do not overheat water and other liquids. Water and liquids heated in the microwave can be heated to boiling but not appear to be boiling. Disturb that water (that is, move the cup), and it can erupt into big, hot splashes that can cause severe burns. To avoid superheated water, never place water in a microwave for long periods of time.

Bacteria. Microwaves heat unevenly. This means that larger portions of foods may not cook all the way through.

  • Always cook larger pieces of meat on medium for a longer time, rather than high on a shorter time. to ensure the meat is fully done.
  • If your microwave does not have a turntable, stop the microwave and stir the food halfway through the cooking time. This helps ensure that the food is fully cooked and reduce the risk that bacteria might linger in the food.
  • Use a meat thermometer to check the temperature of cooked meats, poultry, and eggs. Check in several places. Red meat should reach 160° F, poultry 180° F, and egg casseroles 160° F. Fish should flake with a fork. Leftovers should reach 165° F.
  • Do not cook whole, stuffed turkey in a microwave. The stuffing might not become hot enough to kill harmful bacteria.
  • Do not use microwave ovens in home canning. It is believed that microwave ovens do not produce or maintain temperatures high enough to kill harmful bacteria that can occur when canning some foods. Conventional ovens should not be used for canning, either, for the same reason.

Metals. Generally, metal pans, aluminum foil, or other metal objects should not be used in a microwave. Microwaves are reflected by metal, which can cause dangerous arcing and damage the oven.

  • Never use metals in microwave ovens unless the manufacturer’s instructions specify that it is safe to do so.
  • Do not microwave using brown paper bags, as they can contain tiny amounts of metal.

Plastics. Most plastics fare well in microwave ovens, because the microwaves pass right through them. But heat from food or liquid can transfer to the plastic and melt it. While there’s no truth to the internet rumor that microwaving leaches dioxins into foods (plastics don’t contain the precursors needed to make dioxins)you don’t really want to eat plastic.

  • Use only microwave-safe plastics in your microwave. Reusable plastic containers marked “Microwave Safe” are tested for 240 hours in microwaves.
  • Avoid thin plastic wraps and plastic grocery bags, which can melt because of the heat.
  • Never microwave food in yogurt containers, margarine tubs, or other plastics not marked “Microwave Safe.” The plastic may melt from the heat of the food and water in it, leaching chemicals.
  • Only use containers for microwave foods – for instance, a frozen dinner – once. The polymers in the plastics can start to break down during a second round in the microwave.

Empty ovens. Microwaves need water to work. Most ovens are not designed to be run empty, as there is nothing to absorb the microwaves.

  • Never run your oven without anything in it.

Damaged ovens. If your microwave is damaged, send it to the recycling center. While microwaves are tightly regulated to ensure that only very low levels of microwaves escape – most of which dissipate within one-to-two feet – older microwaves with damaged seals can present a hazard. Tip: Read the instruction manual that came with your microwave. Manuals include information about what type of materials you can use safely in your particular oven.

Overweight? Don't Blame Your Microwave Oven

Rates of obesity and diabetes have risen dramatically since the introduction of microwave ovens. But if microwave ovens contribute to those pandemic problems, it’s not because of some mysterious effect of microwave radiation on food. It’s more likely because microwaves allow us to cook food quickly and consume it quickly. In addition, many foods designed for the microwave are high in fat, calories, and sodium. 

But here's the key: It’s not the microwaves in your oven that cause health problems: It’s the food you cook in that microwave oven.

So is there any reason to bake, broil, sauté, poach, or otherwise heat your food? Sure. Taste, texture, preference, and more. I’m the first to say I’ll take my potatoes baked in a conventional or convection oven, if given the choice. But when you’re in a hurry, or want to quickly cook vegetables and preserve nutrients, or you want to reheat leftovers, a microwave is a good option.

On a night when your alternative might have been a calorie-laden burger from a fast food joint, using your microwave oven to cook a meal of high-fiber vegetables, whole grains, and other wholesome foods might be the healthiest choice you can make.

References

Best ways to clean kitchen sponges. J Environ Health. 2007 Sep;70(2):57.

de la Fuente M.A., Olano A, Juárez M. Mineral balance in milk heated using microwave energy. J Agric Food Chem. 2002 Apr 10;50(8):2274-7.

Dunning, B.  (2007, Sept 28). “Are Microwave Ovens Safe?” Available at http://skeptoid.com/episodes/4080

Environmental Protection Agency. Ionizing and Non-Ionizing Radiation. (March 25, 2011). http://www.epa.gov/radiation/understand/index.html

Mercola, J. (1994). The Proven Dangers of Microwaves. Mercola.com. Available at http://www.mercola.com/article/microwave/hazards2.htm

Mercola, J. (2010). Why Did the Russians Ban an Appliance Found in 90% of American Homes? Mercola.com. Available at http://articles.mercola.com/sites/articles/archive/2010/05/18/microwave-hazards.aspx#_edn4

Mikkelsen, Barbara.  (2006, August 22). Boiling Point. Available at http://www.snopes.com/science/microwave/plants.asp

Santos Ferreira C., Amato Neto V., Gakiya E., Bezerra R.C., & Alarcón R.S. (2003). Microwave treatment of human milk to prevent transmission of Chagas disease. Rev Inst Med Trop Sao Paulo. 45(1):41-2.

Tacken K.J., Vogelsang A., van Lingen R.A., Slootstra J., Dikkeschei B.D., & van Zoeren-Grobben D. (2009). Loss of triglycerides and carotenoids in human milk after processing. Arch Dis Child Fetal Neonatal Ed. Nov;94(6):F447-50. Epub 2009 May 4.

Photo credits:

Microwave Bento by moogs (Ramil Sagum) via Flickr Creative Commons. http://www.flickr.com/photos/anjin/

Microwave Food by eliazar via Flicker Creative Commons

Smeg Microwave by cookipedia

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Good question. There's little

Good question. There's little research on the specific topic of nutrient loss in reheating leftovers, but the same general guidelines would seem to apply: Heating food destroys nutrients, at least to some degree. It doesn't matter whether it's baked, boiled, fried, or microwaved. Because microwaved food is subjected to the heat source for less time, fewer nutrients are destroyed than if you were to use other heating methods.

The belief that microwave

The belief that microwave cooking retains more nutrient is tossed upon the principle that cooking destroys nutrients. Since microwaves cook in less time so they retain more nutrients. It is rather silly to believe microwave retains nutrient. When two groups suggest conflicting reports, the common sense alone tells you to stop and think. Between the two the group that have a hidden self interest behind their suggestion, then that group is not trust worthy as they could be an appointed group to manipulate things to accomplish their agenda(selling microwaves or some thing serious). These groups are either arrogant or paid agents to promote somebody's business. The group that suggest something without any personal benefit on their part is the group to believe. Because by following them it isn't helping them rather you alone. It is pathetic to blame them as fear mongers or any such sort.

Thanks for the comment. It

Thanks for the comment. It does appear that there are two conflicting perspectives here, doesn't it? But the equation heat + food = (some) nutrient destruction is a valid scientific argument. Take any food and expose to heat by any cooking method -- whether that be microwaving, baking, sauteeing, barbecuing, boiling, or a campfire -- and some nutrient losses will occur. Other changes will occur (for instance, changes in the structure of sugars, or "starches"). Microwave cooking simply lessens the time that the exposure occurs. And compared to boiling, especially, fewer nutrients can leach out into the water.

I am astounded that you list

I am astounded that you list the FDA as credible!

, the author of this blog

, the author of this blog asserts that microwaves are safe because they are ‘non ionizing’ meaning they cannot break molecules apart. Despite not being able to break atoms apart, non-ionizing radiation (such as microwaves) CAN cause physical alterations. For example, sunlight can damage your skin and eyes. Overexposure to radiation can affect tissues by causing molecular damage, DNA mutations, and other changes that can lead to cancer. In a letter entitled “DNA and the Microwave Effect”[19] (sourced as Penn State University, 2001), the author reviews the history of the controversy surrounding the microwave effect and the research findings to date. He explains that, although fundamentals of thermodynamics and physics would tell you the microwave effect is impossible, studies keep turning up evidence of its existence. Some of the main points made in the letter are the following: • Microwave heating and conventional heating may appear identical on a “macro” level, but the two appear very different on a molecular level. • Microwaves are effective for sterilization, which has been studied for several decades. There is controversy, however, is about whether it’s the heat they generate or if it’s something else altogether. • One scientist (Kakita 1995[20] ) was successful in demonstrating that microwaves are capable of extensively fragmenting and destroying viral DNA, something that cannot be accomplished by heating alone. • Multiple studies offer evidence that there are multiple mechanisms for breaking apart DNA without ionizing radiation, but no theory currently exists to explain this phenomenon. Some scientists are taking advantage of the microwave effect and using microwaves in the laboratory to greatly accelerate chemical reactions, sometimes by a factor of a thousand, resulting in the completion of reactions in minutes that formerly took days or months and a lot of toxic chemicals[21] . [19] Penn State University. "DNA and the microwave effect" posted from MailBag (April 8, 2002) [20] Kakita Y, Kashige N, Murata K, Kuroiwa A, Funatsu M and Watanabe K. "Inactivation of Lactobacillus bacteriophage PL-1 by microwave irradiation" Microbiol. Immunol. 1995;39:571-576. [21] Adams C. (May 6, 2005) "Does microwaving kill nutrients in food? Is microwaving safe?" The Straight Dope

An independent researcher?

An independent researcher? Why not just tell us who is providing him with lab equipment and feeding his family. Also, he does not publish his own research only a few that need reinterpretation to seem to agree with his theses: "For example, Welt (1994) investigated the effects of microwave irradiation on Clostridium spores and found no additional lethality caused by microwaves that could not be accounted for by conventional heating. However, spores may not be representative of microwave irradiation effects on active growing bacterial cells. The results of this and other experiments showed that controlling the temperature prevented biocidal effects, and this was taken as conclusive evidence that the microwave effect did not exist. However, the assumption that the microwave effect is independent of, and separable from, temperature was always implicit in these studies, but was never acknowledged." This is a good example of his reinterpreting and the careful reader will detect others.

This article does not discuss

This article does not discuss effects of microwaves on reheating already cooked food. Do the nutrients stay preserved when food from the fridge is reheated?

It also doesn't address BPA

It also doesn't address BPA and pthalates in plastics, and the fact that they ARE often in plastic that may be used in a microwave. This article seems to be accurate by omission only.

It may be convenient to cite

It may be convenient to cite omissions but usually just proves to what extent the amount of unaddressed issues are left, not being covered by you when pointing out just one omission. The author didn't appear to be indifferent to all aspects of microwave study, the drive of the article indicated exposing myths. Had this article been an all-inclusive volume of all things microwave, it would be terrabytes voluminous. However, in keeping with the clear, simple nature of the author's positioning of facts, I would have liked to read just one more aspect not covered (or omitted), regarding the necessity of the small holed screen and what makes it so important to the oven user. Microwaves curl and can't pass through, protecting anyone standing next to it. No huge conspiracy there though, so citing omission wouldn't be sensational or provocative, now would it?

I found this article to be

I found this article to be refreshing and to touch on all points of cooking with heat and it's effects on changing chemical composition of food. I think use should use caution with any method of cooking.