Microwave ovens are very popular kitchen appliances which are used for reheating previously heated or cooked foods and cooking a variety of foods.
They are often suspected as a dangerous devices which can affect health, change nutrients structure, decrease the vitamin content and increase the risk of getting cancer.
In this article we would like to confront the common believes vs scientific evidence. First, let's find out how the microwave oven works.
How does a microwave oven work?
Typical microwave oven operates at a frequency of 2.45 GHz and generates output power of 500W and generates waves approximately 12 cm long .
The microwave oven's heart is a magnetron – a device which generates a non-ionizing electromagnetic radiation and passes it through the food.
This induces polar molecules (mainly water as H2O as a bipolar molecule which has a negative charge from oxygen atom and a positive charges from to hydrogen atoms, but also by fats and sugars) in the food to rotate accordingly to the magnetic field.
The polar molecules start to spin and try to keep up with constantly changing magnetic field. Spinning molecules generate a heat as they encounter molecular frictions and collisions. This process is known as a dielectric heating .
The microwave energy is changed to heat as it is absorbed by food, and does not make food 'radioactive' or 'contaminated.'.
Microwaves and health concerns
Acute exposure to high levels of microwaves can cause a painful burns. The testicles and lens of the eyes are particulary sensitive to intense heat, which can kill the sperm, causing temporary sterility and in second case cataracts.
However these effects can only be caused by the exposure of large amounts of microwave radiation, which is far more than 5mW limit for microwave oven leakage .
Jauchem J.R has reviewed literature on the possible effect’s of low-level radio-frequency (RFE) (3kHz to 300GHz) on cardiovascular, reproductive and immune systems.
He concluded that there is only weak evidence in relationsh to RFE and any releated topics above with no cuurent evidence.
Kleinerman et al has undertaken study which has shown that extremely low frequency electromagnetic fields from commonly used household appliances are unlikely to increase the risk of brain tumors .
The newest data suggest there is no significant link between microwave usage and health problems unless new research on low-frequency radiation influence on a health proves otherwise. However precautions should be recommended.
Do not tailgate
If you want to use mivrowave oven safely, you should not stay near to microwave oven once operating (if you can go to a different room do it, if not keep at least 1 m distance from it) as studies has been shown that radiation measured at 20 inches (approximately 0.5 m) away from an oven is hundred times lower than at 2 inches (approximately 5 cm) .
The FDA have set emission standards for new microwave ovens at a power density of 5 mW/cm2/5 centimeters away from any point on the outer surface of the oven.
Typical oven have a leakage on the level of 0.2 mW/cm2/5 cm away from the appliance .
Bear in mind that dirt, mechnical damage, everyday detoriation can eventually reduce the effectiveness of door protection and increase the leakage.
If your concerned about the level of radiation you can try to and buy hardware to store the leakage detectors to measure it.
Keeping a microwave oven in good condition and not tailgating once the oven is operating will reduce the health risk of leakage.
Safety of plastics containers used for the microwaving
Molecules polarity can explain why some of the plastics, glasses and ceramics are considered as microwave safe” so they molecules don't behave like water dipols, and they are not disturbed by magnetic fields shifting.
Plastics as takeout containers, plastic water bottles, plastic tubs, jars made to hold margarine, yoghurt, mayonnaise, mustard etc. are NOT microwave safe.
You should always look for the symbol „microwave-safe” (three lines of waves, one above the other) on the containers which has been designed and tested to NOT leach the toxins – also don't mistake the recycling sign with microwave-safe one’s
Also, you might want to consider only glass and ceramics (as the most neutral food storage materials), as some plastics can contain phthalates, used as plasticizers in manufacture which can acts as an endcrine discruptors compounds (EDC).
There is common belief that microwave oven cook food „inside out”, however this is untrue. In fact, the outer layers are heated primarily by the microwaves while the inside is cooked mainly by the conduction of heat from the hot outer layers .
Microwaving is very fast and efficient cooking method as heating take place in the food.
However the heat might be distributed unevenely due to uneven distribution of microwave radiation as well as different rates of absorbtion in different parts of the food.
Food higher in the water content (i.e. vegetables, fish, meat) is heated quicker than other food (i.e. cereals).
The microwave radiation is changed to heat as it is absorbed by food and does not make food 'radioactive' or 'contaminated' .
Effects of microwave cooking on the nutrients retention
According to Cross and Fung, microwaving results in higher moisture losses in comparison to conventional methods, but the effect on proteins, lipids and minerals is minimal .
Klein has concluded that nutrient content and retention of microwaved-cooked or reheated foods is equal or better that products prepared conventionally or kept in foodservice operation .
Lopez-Berenguer et al study about influence of microwave cooking on bioactive compounds of broccoli showed that the level of all studied compounds (glucosinolates, phenolic compounds, minerals, and vitamin C) except the minerals have been decreased.
They also found that the longer the microwave cooking time, the higher the amount of nutrients and volume of water is lost .
Hoffman et al have shown that microwave cooking has equal or better retention of nutrients vs conventional cooking for thiamin, riboflavin, pyridoxine, folacin, and vit C.
Additionaly microwaved bacon had lower levels of nitrosamines (cancer causing compounds) in comparison to conventionally cooked .
Another study suggested that microwave blanching is 3-4 times more effective that boiled water blanching in water-souble witamins retention (folic acid, thiamin, riboflavin) with the exception of vitamin C .
Microwaving is a fast and efficient form of heating and cooking food. Microwave oven generates a magnetic field causing polar compounds (mainly water dipols) to spin accordingly which produces heat in the food.
When comparing different form of cooking methods, microwaving seems to be reasonable in terms of the nutrients preservation and processing time.
The common belief that any trace of radiation retains in the food is a myth. After you open the doors or timer stops the microwaves are not generated by the magnetron (microwave's heart).
The concern about microwave leakage can be minimized by not staying close to the microwave oven once operating, keeping it clean and in good condition (seals, doors).
- Ng K.H., Gan S.K., Microwave-stimulated fixation for electron microscopy using domestic microwave oven. Malays J. Pathol. 1990 Jun; 12(1): 27-33
- https://en.wikipedia.org/wiki/Microwave_oven as seen on 09/07/2016
- Zaman Syed Sabbir http://www.slideshare.net/Lincoln2015/microwave-oven-54329300 as seen on 09/07/2016
- http://www.fda.gov/RadiationEmittingProducts/ResourcesforYouRadiationEmittingProducts/ucm252762.htm as seen on 09/07/2016
- Jauchem J.R., Effects of low-level radio-frequency (3kHz to 300GHz) energy on human cardiovascular, reproductihve, immune, and other systems: a review of the recent literature. Int J. Hyg Environ Health. 2008 Mar; 211 (1-2): 1-29
- Kleinerman R.A., Linet M.S., Hatch E.E., Tarone R.E., Black P.M., Selker R.G., Shapiro W.R., Finde H.A., Inskip P.D., Self-reported electrical appliance use and risk of adult brain tumors. Am J Epidemiol 2005 Jan 15; 161(2): 136-46
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- Cross G.A., Fund D.Y., The effect of microwaves on nutrient value of foods. Crit Rev Food Sci Nutr. 1982; 16(4): 355-81
- Klein B.P., Retention of nutrients in microwave-cooked foods., Bol Asoc Med P.R. 1989 Jul; 81(7): 277-9
- Lopez-Berenguer C., Carvajal M., Moreno D.A., Garcia-Viguera C., Effects on microwave cooking conditions on bioactive compounds present in broccoli inflorences. J Agric Food Chem 2007 Nov 28; 55(24)
- Hoffman C.J., Zabik M.E., Effects of microwave cooking/reheating on nutrients and food systems: a review of recent studies., J Am Diet Assoc 1985 Aug; 85(8):922-6
- Osinboyejo M.A, Walker L.T., Ogutu S., Verghese M., Effects of microwave blanching vs boiling water blanching on retention of selected water-soluble witamins in turnip greens using HPLC. National Center for Home Food Preservation, University of Georgia. Retrieved 23 July 2011