Heather Bedard, C.H.E.
Continuing on this theme of nutrient gains or losses, critics of the microwave use a study done in 2001 on the influence of heating on the anticancer properties of garlic.[1] One of these properties is alliinase. Critics say that almost all of the alliinase is lost when heating garlic in the microwave for just 60 seconds. They often fail to mention that this type of loss is also seen in 45 mins of heating in an oven and that heat in general will cause this loss. On the other hand, advocates of the microwave use a study from 2009 titled, “Influence of Cooking Methods on Antioxidant Activity of Vegetables.” to refute the claim that antioxidants in garlic are damaged by microwaves.[2] However, this study is generic and is not a good resource for determining that heating doesn’t damage garlic.
While some critics agree that heat of any kind will cause some nutritive loss, many go a step further by claiming that the violence of the energy of the thermal radiation compared to the less energetic conventional heating methods creates byproducts that the human body isn’t designed to process. These byproducts, they say, are not due to the effects of thermal damage but also biological damage. It’s important to understand that microwaves heat food quickly which causes the molecules to vibrate faster than other heating methods. However, this intense level of vibration doesn’t mean that that the food compounds break down any differently than other heating methods over time, it’s just that they get heated faster.[3] If this topic is still a concern, the USDA has a release describing the nutrient retention in various foods with all different cooking methods.[4]
Moreover, many critics of the microwave oven claim that the extreme friction of the molecules caused by the electromagnetic waves results in the degradation and depolarization of the food. In some ways this is true. Although I couldn’t find any reference to a study supporting this in the articles that the claims were made in, there is an article on “Microwave Processing: Effects and Impacts on Food Components”, which explains the process of degradation in detail.[5] All components of food are affected by the microwave including carbohydrates, proteins, and fats. According to this article, the microwave exhibits less degradation on the molecules than does conventional heating methods, but there is some degradation. Likewise, I couldn’t find any studies supporting that food can be depolarized. However, the above study shows that the various food molecules do spin to find their polarity. How this effects the food’s nutrition or the body’s processing of that food is a realm for more research. If by the degradation and depolarization claim, the critics are referring to degradation in food texture or quality, this has been studied to some extent. Taste, texture, flavors, and nutritional characteristics change based on how the food is cooked. In conventional heating methods, some of the flavor profiles of the food changes based on the method used. For example, grilled food tastes “grilled” because of the type of fuel used in the grill and the level of char on the food. One of the reasons that food tastes different when cooked in the microwave is because it doesn’t introduce additional flavors – it simply heats. This is why in blind taste tests people can taste the difference in microwaved foods. This is not because the food is of lesser quality; there are just no added flavor profiles that one may be used to tasting. Some of the mechanisms of the change of texture in microwaved foods include internal boiling, moisture loss, and the amount of starch in the food. This is outlined in a study on the mechanisms of objectionable textural changes by the microwave reheating of foods.[6]
Continuing on to carcinogens, proponents of the microwave stave off concerns that the heat of the microwave can cause reactions in food that are carcinogenic. They point to the fact that microwaves do not heat the environment to a particular temperature. Because of this, the measurement of heat is inherently difficult to make. As stated at the beginning of this paper, the microwave works by exciting molecules to produce friction and heat. So, the longer an item is in the microwave the hotter it gets. The microwave isn’t technically producing heat, the molecules in the food are. Due to their water content, most foods don’t get above 100-212 degrees Fahrenheit which is the boiling point of water. This being said, as the water evaporates, the food will eventually become hot enough to begin producing carcinogenic compounds at some point. Concerning levels of carcinogenic materials are highly unlikely unless you are purposely over-cooking your food. Microwaves do not cause searing and burning like a traditional oven or grill might. Thus, heterocyclic amines (HCA) and polycyclic aromatic hydrocarbons (PAHs) are unlikely to form. These compounds are made from creatines and amino acids when exposed to high heat and burning. When making their argument regarding the creation of carcinogens through microwaving, critics usually fail to mention that creatine is found only in meat and so if you are microwaving fruits and vegetables your exposure is reduced even further. Another study titled, “Effect of Microwave Pretreatment on Heterocyclic Aromatic Amine Mutagens/Carcinogens in Fried Beef patties”, shows that beef patties microwaved before frying actually reduced heterocyclic amines three to nine-fold.[7] Furthermore, any foods that contain sugars, fats, or proteins are susceptible to forming Advanced Glycation end products (AGEs) at high heat. AGEs are another type of carcinogen. AGEs usually become a problem at temperatures in excess of 446 degrees Fahrenheit. As stated above, most microwaves don’t get much higher than 212 degrees Fahrenheit. While heat can cause the formation of AGEs, unless you’re scorching your food in the microwave this is less of a concern. Additionally, another interesting expression of a carcinogen in foods is acrylamide. This carcinogen can be formed by microwaving at high power but can be reduced in foods if they are thawed or blanched in the microwave on low power before they are fully heated in the microwave.[8] The bottom line is, if one is concerned about carcinogens in food due to microwaving, the same must be said for any other method of heating.
Many of the people warning that microwaved foods cause cancer cite studies done by German and Russian researchers. I could not find these actual studies published in their original form anywhere, nor could I find any studies proving that microwaved foods themselves cause cancer. In some instances, it is claimed that because some food causes the creation of free radicals when heated, these foods cause cancer in the stomach and intestine. Studies like, “When Theory and Observation Collide: Can Nonionizing Radiation Cause Cancer?” are used to prove this point.[9] However, the critics using this study always specify that the foods were heated by microwaves - when any heat application would cause the same effect. The truth is that any food that causes free radicals and the following oxidative stress could lead to cancer. However, hypothesizing and relying on theories and correlations do not prove causation and should not be stated as such. Avoiding the carcinogens in food can be done by microwaving at low power and not overcooking your food.
Lastly, there is another concern regarding the ingestion of microwaved food potentially causing immune system deficiencies through lymph gland and blood serum changes. This claim is based on the research of Hans Hertel who wrote a paper detailing his private research on the negative effects of microwaved food on the human body. His singular study showed leukocytosis (an increase in white blood cells), increased cholesterol values and anemic tendencies in people who microwaved their food over an 8 week period. Although this study is quoted by nearly every natural health blogger you can think of, the only hard evidence I found on this research is a PDF of the court case of Hertel v. Switzerland in which his research is documented for the court.[10] Unfortunately, his actual paper was never published due to the court ruling and there has been little to no research on the effect of microwaved food on blood serum and lymph glands in humans. Hertel’s research is preliminary and needs stronger scientific evidence to prove that the effects he found are as serious to the general population as the paper seems to claim. Potentially, there are a few mechanisms of action that have been studied that could eventually lead to confirming the above claims with some limitations. One mechanism would be ROS or free radicals and how they increase cholesterol through oxidative stress on the body.[11] This process, as explained in a previous paragraph, is exemplified by any food that creates free radicals and not necessarily by the method of heating. Another mechanism is shown in a study used by critics of the microwave titled, “Effect of Ingestion of Microwaved Foods on Serum Antioxidant Enzymes and Vitamins of Albino Rats.”[12] While this study did show a reduction of antioxidant enzymes and vitamins A and E with the ingestion of microwaved foods, the study did not compare other heating methods and so there is no way of knowing if these results would be similar if other heating methods were used. More research needs to be done in this area.
Aside from the debates on a food’s nutritive quality and the effects on the body, the bigger issue may be what you are microwaving your food in. One of the biggest concerns is that microwaving food in plastic containers can cause a leaching of the plastic chemicals into the food. BPA (Bisphenol A) is probably the most well-known chemical that people are familiar with in plastics. This includes plastics known to be “microwave safe”. Because its molecular structure is very similar to that of estrogen, BPA interacts with estrogen receptors and has been found in human blood, urine, and placentas and shows developmental toxicity on reproductive organs.[13] The EPA (Environmental Protection Agency) allows 10x the amount that the European Union does for a no-observed adverse-effect level, from 50mg/kg/day compared to 5mg/kg/day. Despite this, the FDA (Food and Drug Administration) continues to proport that BPA in low doses is fine and that they will continue to review any issues.[14] This notwithstanding, BPA is slowly being removed from many products. There are many complicated processes involved in low-dose BPA and its effects on humans and more research needs to be on the exact amount of low-dose BPA one can ingest without adverse effects. Additionally, there are many other chemicals that have been known to leach or migrate into foods in containers made to be microwave safe. These include polyethylene terephthalate and benzene. The amount of chemical migration depends on what the chemical components of the container are, the composition of the food, and how long it is cooked.[15] There is currently no FDA definition for microwave safe beyond the regulation of the plastics that are allowed for food contact. This could be taken to be understood that any leaching of chemicals is less than what is considered safe levels in animals. In general, most people accept “microwave safe” as being an item that won’t melt or warp under high heat. The generally accepted definition of “microwave safe” has nothing to do with chemical leaching and the definition is not unilaterally recognized. Because of the varying levels of chemicals in each plastic container and the difficulty in determining the amount of chemicals migrating into the food, it would be safer to microwave food in glass containers when possible.
On the subject of food safety, due to the uneven way that the microwave cooks the food, one should be sure to stir the food before eating to ensure an even distribution of heat. This applies to cooking raw meats in the microwave as well. To be sure that the food has enough heat to kill bacteria, only heat foods that have been cooked thoroughly using another method.
Answering the question, “Is it OK to cook my food in the microwave” is not just a simple “yes” or “no” answer. The answer depends on the impetus of the question being asked. If the question is asking whether or not the food cooked a microwave is safe to consume, I found the available research to support the belief that the food is not irradiated or changed in any meaningful way compared to conventional heating methods. If the question is asking if eating food that is microwaved will cause health complications or disease, then I found that the research points to the type of food and the packaging it’s cooked in being an issue more than just a cut and dry “yes” or “no”. While I found the arguments and quality of evidence to be less than desirable on both sides of the question, the current available research seems to point to the idea that if you microwave healthy food in glass containers, you will be just fine.
[1]Song K, Milner JA. The influence of heating on the anticancer properties of garlic. J Nutr. 2001;131(3s):1054S-7S. doi:10.1093/jn/131.3.1054S [2]Jiménez-Monreal AM, García-Diz L, Martínez-Tomé M, Mariscal M, Murcia MA. Influence of cooking methods on antioxidant activity of vegetables. J Food Sci. 2009;74(3):H97-H103. doi:10.1111/j.1750-3841.2009.01091.x [3]Tang J. Unlocking Potentials of Microwaves for Food Safety and Quality. J Food Sci. 2015;80(8):E1776-E1793. doi:10.1111/1750-3841.12959 [4] https://www.ars.usda.gov/ARSUserFiles/80400525/Data/retn/retn06.pdf [5]Hao Jiang, Zhigang Liu & Shaojin Wang (2017): Microwave processing: Effects and impacts on food components, Critical Reviews in Food Science and Nutrition, DOI: 10.1080/10408398.2017.1319322 [6]Mizrahi S. Mechanisms of objectionable textural changes by microwave reheating of foods: a review. J Food Sci. 2012;77(1):R57-R62. doi:10.1111/j.1750-3841.2011.02515.x [7]Felton JS, Fultz E, Dolbeare FA, Knize MG. Effect of microwave pretreatment on heterocyclic aromatic amine mutagens/carcinogens in fried beef patties. Food Chem Toxicol. 1994;32(10):897-903. doi:10.1016/0278-6915(94)90087-6 [8]Michalak J, Czarnowska-Kujawska M, Klepacka J, Gujska E. Effect of Microwave Heating on the Acrylamide Formation in Foods. Molecules. 2020;25(18):4140. Published 2020 Sep 10. doi:10.3390/molecules25184140 [9]Havas M. When theory and observation collide: Can non-ionizing radiation cause cancer?. Environ Pollut. 2017;221:501-505. doi:10.1016/j.envpol.2016.10.018 [10] https://elaw.org/content/european-court-human-rights-hertel-v-switzerland-5919978431049-1998825-european-court-human- [11] Laurence Gesquière, Nadine Loreau, Anne Minnich, Jean Davignon, Denis Blache, Oxidative stress leads to cholesterol accumulation in vascular smooth muscle cells, Free Radical Biology and Medicine, Volume 27, Issues 1–2, 1999, Pages 134-145, ISSN 0891-5849, https://doi.org/10.1016/S0891-5849(99)00055-6 [12] Benedict C. Eke, Norbert N. Jibiri, Evelyn N. Bede, Bede C. Anusionwu, Chikwendu E. Orji, Chinwe S. Alisi, Effect of ingestion of microwaved foods on serum anti-oxidant enzymes and vitamins of albino rats, Journal of Radiation Research and Applied Sciences,Volume 10, Issue 2, 2017, Pages 148-151,ISSN 1687-8507, https://doi.org/10.1016/j.jrras.2017.03.001 [13]Gao H, Yang BJ, Li N, et al. Bisphenol A and hormone-associated cancers: current progress and perspectives. Medicine (Baltimore). 2015;94(1):e211. doi:10.1097/MD.0000000000000211 [14] https://www.fda.gov/food/food-additives-petitions/questions-answers-bisphenol-bpa-use-food-contact-applications [15] Bhunia, Kanishka & Sablani, Shyam & Tang, Juming & Rasco, Barbara. (2013). Migration of Chemical Compounds from Packaging Polymers during Microwave, Conventional Heat Treatment, and Storage. Comprehensive Reviews in Food Science and Food Safety. 12. 10.1111/1541-4337.12028.