Many people in fitness are completely freaked out by microwave cooking. They’re worried that the microwave destroys nutrients. Ruins food quality. Poisons our bodies.
Are any of these claims true? Should we be worried about microwave cooking (or reheating)? In this article we’ll find out the truth.
- Unprocessed foods.
- Whole foods.
- Local foods.
- Microwaved foods.
Which one of those is not like the other?
When we use a microwave, what purpose does it serve?
Are we using it to reheat our “unprocessed food” leftovers from a recipe we made after shopping at the farmers market? Or are we using the microwave to get that Pop-Tart juuuusssst right?
Up to 93% of American homes have and/or use microwaves, so obviously there is something appealing about them.
But do any of us really know the long-term health implications of repeated microwave use? And does microwaving food affect the nutrients it contains?
How microwave ovens came to be
Percy Spencer was building radars in the 1940s and discovered that microwaves from radars melted a candy bar in his pocket.
Fast forward seven years and we had the first “radarange” in 1947 at a Boston restaurant. It weighed about 700 pounds and cost nearly $5000. People weren’t excited about cooking food with “radar,” so the name was changed to “microwave oven”.
The first popular microwave for home use was introduced in 1967.
As more women were entering the workforce, anything that saved time in the kitchen was welcome. An advertising campaign coincided with housewives using microwave ovens followed by young female sales personnel travelling around North America proclaiming their benefits.
How microwaves work
Inside-out cooking
Conventional cooking transmits heat to the outside food by convection (baking), radiation (broiling), or conduction (frying). This heat then makes its way to the inside of the food. This can take a while, as anyone who’s frantically tried to roast a semi-defrosted turkey can attest.
Microwaves, by comparison, start on the inside of the food.
Microwaves are a form of electromagnetic energy (radiation), like radio waves or light waves. When absorption of microwave energy interacts with molecules in food, heat is generated and the food is cooked (think of rubbing your hands together really fast).
The source of radiation in a microwave oven is the magnetron tube, which converts an electric current to electromagnetic radiation. Microwaves can travel through glass, but metals reflect them. This is why microwave doors have a metal screen.
Energy use
Because they heat the food from the inside out (rather than outside-in), microwave ovens have a better cooking efficiency (the % of energy that heats food during the cooking cycle) than electric or gas convection ovens.
| Oven type | Efficiency |
|---|---|
| Microwave | 57% |
| Electric convection oven | 17% |
| Gas convection oven | 9% |
Microwaves also use less electrical power than conventional type electric ovens.
| Oven type | Watts |
|---|---|
| Microwave | 750-1100 |
| Toaster oven | 1200-1700 |
| Electric oven | 3000-8000 |
The effects of microwaves on food
Nutrients
Although you may have heard that microwaves kill nutrition, that doesn’t seem to be true.
Microwave ovens usually don’t destroy nutrients in food. And in some cases, preparing food in a microwave might actually promote nutrient retention.
Nutrients are leached from food during any form of cooking, especially when the food is cooked for a long period of time with high amounts of water. So, for example, boiling carrots might strip nutrients much more drastically than microwaving them, because the carrots’ nutrients might get washed away with the boiling water.
However, since we haven’t discovered all the compounds that make up food, we’ll likely never know all of the outcomes that microwaving has on nutrients.
Protein
Protein quality seems to be fine with microwave heating. Some data indicates that amino acids and vitamin B12 may be converted to inactive forms.
But on the flip side, availability of some amino acids might be improved, since no surface browning occurs. And microwave heating might lead to destruction of trypsin inhibitors in beans. Bonus!
Breast milk
Microwaving breast milk breaks down the antibodies and vitamin B12 (this also occurs with conventional boiling, but it takes about 25 minutes or more).
By the way, speaking of organic fluids, heating blood for transfusions in microwave ovens can result in hemolysis (but hasn’t been shown to damage DNA).
Food safety and carcinogens
Microwave cooking forms fewer nitrosamines and AGEs on meats than conventional cooking methods. For more on AGEs, see here.
Taste
Taste preferences are individualized. Still, restaurants usually don’t advertise “microwaved green beans” on the menu.
Microwave cooking doesn’t result in surface drying or browning reactions, so this alters the flavour and appearance of foods (especially meats and breads).
Some microwavable foods will come with a gray paperboard for heating. This paperboard contains an extremely thin metal coating of resistant polymer film which absorbs microwave energy, converting it into heat for browning. Certain additives can also be put on the surface of food to achieve this effect. Gosh, now I’m having flashbacks of microwavable pizzas in junior high.
The health effects of microwaves
Ahhh, the 1980s. Micro Machines, slap bracelets, American Gladiators and Hans Hertel.
Wait… who’s Hans Hertel? Well, Hertel and Bernard Blanc, two Swiss scientists, did some experiments with microwave cooking.
They found subjects to have lower hemogloblin and higher white blood cells and blood cholesterol after eating microwaved food. However, this data was never published in a peer reviewed journal.
The Swiss appliance industry wasn’t excited about these results and took the scientists to court. Hertel and Blanc were convicted of interfering with commerce, but the ruling was later reversed (see reference section for more info).
Electromagnetic radiation
When microwave ovens were first available to the public, tests showed that they leaked excessive electromagnetic radiation. This type of radiation is non-ionizing, which means that it isn’t the type of “radiation” you’d associate with Homer Simpson and Chernobyl — it’s in the form of waves.
Early microwave ovens worked by sending wavelengths similar to many of today’s phones (915 mHz). The main difference between phones and ovens is that the power needed to operate a microwave oven – about 1000 watts – is much greater than that needed for a cell phone. Cell phones operate with less power but at the same wavelength as microwave ovens.
In the United States, the FDA allows some radiation leakage. In the 1970s, Consumer Reports declared that microwave ovens were “not recommended,” and the Soviet Union actually banned microwaves for a short time (no countries ban them today).
Exposure to radiation is highest within two inches of the microwave. Yet, the amount of electromagnetic radiation we are exposed to from microwave cooking is less than cell phones (measured cumulatively).
When our body absorbs microwave radiation, we take on the energy as heat. Some tissues are sensitive to this.
Strong fields of electromagnetic radiation may raise cancer risk, affect the nervous system, and promote other problems (such as Alzheimer’s disease). There is a correlation between microwave cooking and oral cancers/salivary gland tumors, but this might be due to the production of heterocyclic amines in food.
Some data indicate that cooks may have higher risks of cancer due to microwave radiation exposure, but the body of evidence is still not clear on this.
If our only exposure to electromagnetic frequencies is via microwave cooking, it probably wouldn’t be a big deal. But add up total exposure and it becomes a concern.
We absorb EM radiation from power lines, cell phones, airplane flights, computers, fridges, and so forth. There is growing evidence that effects of microwave radiation add up over time.
However, the radiation from microwave ovens alone is so low that it shouldn’t damage DNA. And there is no legit data indicating a direct negative impact of microwave ovens on human health.
“We don’t have a solid position on the possible health risks from exposure to microwaves due to inconclusive research. The real question remains whether there could be cumulative effects.”
–Norbert Hankin of the Environmental Protection Agency (EPA)’s Center for Science and Risk Assessment
Plastics
Many plastics, when heated, release toxic and endocrine (hormone) disrupting compounds into the food. So don’t microwave food in plastic, especially in plastic containers not labeled “microwave safe”. And styrofoam… well, just don’t go there.
The term “microwave safe” has mixed support – some say it’s legit, some say it’s not regulated. And by the way, exposing plastic to any type of heat (in the oven, microwave, campfire, etc.) has the same negative outcome. Microwaving just speeds up the process.
And most of us aren’t likely to try to use Tupperware as a frying pan. (Well, at least not after the… unfortunate… incident.)
Dyes haven’t been approved for microwave use, so don’t assume you’re problem-free if you’re using coloured paper towels or paper containers.
Bacteria
Food heated in a microwave oven can have uneven temperature distribution. The food (or part of the food) with the highest water content heats up the quickest. This is why many oven models include a rotating tray: it distributes the waves more evenly.
Uneven food temperatures may allow microorganisms — including Salmonella, Listeria, Clostridia and Campylobacter — to survive.
So when you’re cooking or reheating, make sure the food is thoroughly heated, and occasionally turn or stir food if possible.
The great exploding cup of tea
Heating up liquids in the microwave can prevent bubbles from forming. The water can become overheated past the boiling point.
When the liquid is agitated (say by stirring it or dropping a bag of tea in it), it can erupt. So watch out and don’t set your tea to “volcanic”.
Summary and recommendations
Microwave ovens usually don’t destroy nutrients in food. If using a microwave helps you eat more nutritious foods and less junk food, then keep it.
But there are potential harmful effects from too many electromagnetic frequencies, and doing without a microwave is one way to limit exposure.
If you use a microwave:
- Don’t heat food in plastic.
- Make sure food reaches 160 degrees F in all areas (you have a food thermometer, don’t you?).
- Cover food to help ensure uniform cooking.
- Allow the food to sit a few minutes after microwaving.
- Microwave food only as long as necessary, with little to no cooking water.
- Keep the microwave out of high traffic areas.
If you don’t use a microwave:
- You can eat leftovers cold. If you don’t have to reheat – don’t. Each time we reheat, no matter the method, we are going to lose nutrients.
- Try the stove, including steaming or stir-frying.
- Use the oven, including baking and broiling.
- Consider a toaster oven, which uses less energy than a conventional oven. (Heck, consider a solar cooker. Just sayin’.)
- Heat water in an electric tea kettle.
References
Click here to view the information sources referenced in this article.
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