Are Microwaves Safe?

Microwaves ovens are a very common kitchen appliance used mainly for cooking certain foods or reheating previously cooked foods.  The heating occurs inside the food without warming the surrounding air, which greatly reduces cooking time and is one of the reasons people like microwaves. They are fast, simple, and convenient! In a microwave, within minutes, you can achieve the cooking and baking of foods that would otherwise require hours in a conventional oven or by using other cooking methods.

Are Microwave Ovens Safe?

This is the big question. And although it may seem that the answer should be very obvious, both for those in favor or against microwaves, the truth is that the answer is quite complicated.

Let’s look at what the scientific literature of the last decades has to tell us:

2020 – Effect of microwave and oven drying processes on antioxidant activity, total phenol and phenolic compounds of kiwi and pepino fruits⁶.

Assess the effect of microwave oven and conventional oven drying methods on antioxidant activity, total phenolic, and phenolic compounds of kiwi and pepino fruits. These fruits were dried using a conventional oven (70 °C for 20 h) and a microwave oven (720 W for 3 min). The researchers found that:

• Both drying methods, as expected, significantly decreased the moisture contents of both fruits when compared to controls (non-dried).
• Both also enhanced antioxidant activity and total phenolic content of both fruits.
• Highest improvement observed for microwave-dried fruits.
• Significant increase in catechin and 1,2-dihydroxybenzene content of kiwi and pepino after the drying process.
• Microwave drying \reduced the amount of 3,4-dihydroxybenzoic acid in kiwi and pepino.

Conclusion:

In general, the highest antioxidant activity and phenolic contents were reported in microwave oven dried samples, followed by samples dried in conventional oven and fresh fruits, hence microwave drying could be more useful in fruit drying than conventional drying.

Dried kiwi and pepino fruits contain substantial quantities of phenolic compounds with high antioxidant activity compared to fresh fruits, and thus they are considered as healthy food.

2015 – Unlocking Potentials of Microwaves for Food Safety and Quality¹.

In this study, the author addresses the fear of many consumers who “associate microwave heating with radioactivity and are seriously concerned about possible harmful chemical reactions caused by microwaves.” The author states that “microwaves, unlike X-rays, are not able to create free radicals or disrupt molecular bonds in biological materials,” adding that “the only effects on foods are the results of thermal energy converted from microwave energy.”

Another concern is the exposure to microwaves leaking from domestic and industrial microwave ovens, which is strictly regulated by The Food and Drug Administration (FDA).

2003 – Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking⁷.

Evaluation of phenolic compound (total flavonoid and individual hydroxycinnamoyl derivative) content in the edible portions of freshly harvested broccoli before and after cooking and in the cooking water. The cooking processes evaluated were high-pressure boiling, low-pressure boiling (conventional), steaming, and microwaving.

• Microwave – clearly disadvantageous: high losses of flavonoids (97%), sinapic acid derivatives (74%), and caffeoyl-quinic acid derivatives (87%).
• Conventional boiling – significant loss of flavonoids (66%)
• High-pressure boiling – caused considerable leaching (47%) of caffeoyl-quinic acid derivatives into the cooking water.
• Steaming – minimal loss effects on both flavonoid and hydroxycinnamoyl derivative contents.

Conclusion

Clear disadvantages with the use of microwave ovens, as 97 percent of flavonoids are lost. Steaming provides a greater quantity of phenolic compounds when compared with broccoli prepared by other cooking processes.

2013 – No Major Differences Found between the Effects of Microwave-Based and Conventional Heat Treatment Methods on Two Different Liquid Foods⁸.

Compares the results of heat treatment of milk and orange juice using a microwave and conventional heating. Different heating methods showed similar results in most parameters analyzed, with differences detected only in the color characteristics of the milk samples (in terms of the color coordinates and the brightness index, in an amount that is invisible to the naked eye).

Conclusion

No major differences were found between the effects of microwave and conventional heating of milk and orange juice, except for the color of microwaved milk that differed from control and conventional samples.

2002 – Comparison of the effects of microwave cooking and conventional cooking methods on the composition of fatty acids and fat quality indicators in herring⁹.

Comparison of the effect of different heating methods, using conventional culinary techniques and microwave radiation in the compositions of fatty acids and selected fat quality indicators in filets of herring.

Culinary processes like boiling, grilling, and frying, both conventionally or with a microwave oven, did not reduce omega-3 polyunsaturated fatty acids (PUFAs) and exhibited an insignificant influence on the fat quality indicators. This indicates that these fatty acids have a high durability and a low susceptibility to thermal oxidative processes.

Conclusion

Both conventional and microwave heating did not reduce omega-3 fatty acid content in filets of herring and fat quality indicators differ little between those two methods.

1998 – Effects of Microwave Heating on the Loss of Vitamin B(12) in Foods¹⁰.

Effects of microwave heating on the loss of vitamin B 12 in foods. Raw beef, pork, and milk were treated by microwave heating and then their vitamin B 12 contents were determined.

Appreciable loss (approximately 30-40%) of vitamin B 12 occurred in the foods during microwave heating due to the degradation of vitamin B 12 molecules. 

Conclusion

During microwave heating, there is a conversion of vitamin B 12 to inactive vitamin B 12 degradation products in foods.

1982 – The effect of microwaves on nutrient value of foods¹¹.

Microwave cooking resulted in higher moisture losses compared with conventional methods.

Minimal nutritional effects of microwaves on protein, lipid, and minerals. No report on the effects of microwaves on carbohydrate fraction in foods.

Only slight differences between microwave and conventional cooking on vitamin retention in foods.

Conclusion

No significant nutritional differences exist between foods prepared by conventional and microwave methods. 

What are our conclusions?

Although this article does not cover and is not aimed at covering all available research studies about this subject, the ones presented here often show contradictory results, and its findings can be confusing.

However, here is what we consider important conclusions:

• As with any food heating method, there is a loss of nutrients, vitamins, and minerals, this is very clear for Vitamin B 12.
• Many bioactive compounds and phytochemicals naturally present in raw foods may suffer degradation and be lost.
• Microwaving may alter food properties in other ways, besides their nutritional value, such as color, texture, and flavor.
• Radiation leakage may be a health concern, and although microwave ovens are subject to safety standards that ensure minimal levels of radiation leakage, it is still recommended to stay away from the microwave while it is working.
• Microwaves do not heat up food evenly.
• Certain materials should not be used in a microwave and can lead to dangerous situations.
• Most pre-prepared/precooked foods for microwave heating are almost completely depleted of nutrients, providing usually high calories and low nutrition or health benefits.

 

References

1. Tang J. Unlocking Potentials of Microwaves for Food Safety and Quality. J Food Sci. 2015 Aug;80(8):E1776-93. doi: 10.1111/1750-3841.12959. Epub 2015 Aug 4. PMID: 26242920; PMCID: PMC4657497.
2. “Microwave Oven”. Encyclopedia Britannica. 26 October 2018. Retrieved 23 January 2023.
3. Microwave Oven. https://en.wikipedia.org/wiki/Microwave_oven, accessed
4. Jiang H, Liu Z, Wang S. Microwave processing: Effects and impacts on food components. Crit Rev Food Sci Nutr. 2018;58(14):2476-2489. doi: 10.1080/10408398.2017.1319322. Epub 2017 Aug 14. PMID: 28613917.
5. History of Microwave. Facts and History of Microwave. http://www.historyofmicrowave.com/, accessed Jan 25, 2023.
6. Özcan MM, Al Juhaimi F, Ahmed IAM, Uslu N, Babiker EE, Ghafoor K. Effect of microwave and oven drying processes on antioxidant activity, total phenol and phenolic compounds of kiwi and pepino fruits. J Food Sci Technol. 2020 Jan;57(1):233-242. doi: 10.1007/s13197-019-04052-6. Epub 2019 Aug 27. PMID: 31975726; PMCID: PMC6952493.
7. Vallejo, F., Tomás-Barberán, F. and García-Viguera, C. (2003), Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking. J. Sci. Food Agric., 83: 1511-1516. https://doi.org/10.1002/jsfa.1585
8. Géczi G, Horváth M, Kaszab T, Alemany GG. No major differences found between the effects of microwave-based and conventional heat treatment methods on two different liquid foods. PLoS One. 2013;8(1):e53720. doi: 10.1371/journal.pone.0053720. Epub 2013 Jan 16. PMID: 23341982; PMCID: PMC3547058.
9. Regulska-llow B, Ilow R. Comparison of the effects of microwave cooking and conventional cooking methods on the composition of fatty acids and fat quality indicators in herring. Nahrung. 2002 Dec;46(6):383-8. doi: 10.1002/1521-3803(20021101)46:6<383::AID-FOOD383>3.0.CO;2-L. PMID: 12577584.
10. Watanabe F, Abe K, Fujita T, Goto M, Hiemori M, Nakano Y. Effects of Microwave Heating on the Loss of Vitamin B(12) in Foods. J Agric Food Chem. 1998 Jan 19;46(1):206-210. doi: 10.1021/jf970670x. PMID: 10554220.
11. Cross GA, Fung DY. The effect of microwaves on nutrient value of foods. Crit Rev Food Sci Nutr. 1982;16(4):355-81. doi: 10.1080/10408398209527340. PMID: 7047080.