Microwaves and Nutrients

We have an infant in our midst who is still new to eating solid food. One day my wife and I were talking about heating up our daughter’s food in the microwave to make it more palatable and wondered if using the microwave was “safe”. I believed it would be fine since I trust most of modern technology – not that the microwave would be considered truly modern – but my wife’s concern revolved around the loss of nutritional value as a consequence of the food getting zapped. As it turns out, this is an often-cited issue concerning microwaves and one that I had simply pushed aside. When thinking about the issue I realized it is not without some merit and though I am typically disdainful of fear-driven beliefs without substantial, empirical backing, I decided to check it out.


Microwaves lie on the electromagnetic spectrum between infrared and radio waves, all of which have longer wavelengths than light in the visible range and sit on the opposite end of the spectrum from x-rays and UV. Microwave ovens use microwave frequencies around 2.5 gigahertz which are generated by the magnetron tube after stepping up the AC voltage from your wall socket to a high DC voltage. This frequency of microwaves is absorbed by fats, sugars and, more importantly, water. The microwaves affects the vibration of these molecules and it is this altered atomic motion that generates heat and cooks the surrounding bits. Unlike a conventional oven, the heat is not conducted from the outside in; rather it generates everywhere at once though wave penetration varies by substance and may generate hotspots and uneven cooking. The lack of external heat is also what causes the characteristic sogginess of some food you have probably encountered.


To address the question posed about nutrients, it appears that all legitimate sites state food cooked in the microwave is safe and the loss of nutrients is unremarkable in most foods when compared to traditional cooking methods. (If you wonder how I determine a site’s “legitimacy”, I typically trust sites with .edu in their addresses, especially if it is their own study they are reporting and sites that cite their sources are better than ones which do not, but those with emotional language or pleas concerning humanity or greatness of uncooked foods are out (didn’t humans develop the means to produce fire?). Dancing characters of any sort are also big deterrents.)


The largest cause of nutrient loss is due to heat over time, aka “cooking” – since there are shorter cook times in the microwave, food is often less affected by the cooking than with conventional methods. This is particularly true for blanching since the longer food is in the boiling water, the more nutrients leach out. There is even indication that bacon is better cooked in the microwave since it produces fewer nitrosamines, a carcinogenic by-product, through the process. Some noted exceptions to the above statement include a loss of ascorbic acid, which is damaged at a higher rate than through conventional methods and the deactivation of B12′s active form. Heating breast milk should also not be heated in the microwave because of the effects on it’s anti-infective properties; however, I wouldn’t recommend microwave warmed liquids for babies anyway due to the uneven heating and development of hot spots.


A noted study from Universidad Complutense Madrid in Spain discussed how different cooking methods affected antioxidant levels. They found that, along with grilled and baked foods, food cooked in the microwave maintained the highest levels of antioxidants varying greatly on the individual vegetable and antioxidant with ranges from no loss to around 50% loss from cauliflower, a few vegetables such as carrots, celery and green beans even increasing their antioxidant levels. It was again shown that methods which utilized water, such as boiling and pressure-cooking, were the greatest culprits in causing the loss of antioxidants.


What all this tells us is most foods are fine when prepared in the microwave. Though I prefer the subtle influences that are imparted by slower methods of stovetop simmering and won’t be serving up any roast and potatoes or chicken roulade a la microwave, I don’t feel a twinge of guilt placing my family’s leftovers on the turntable and hitting the “quick cook” button to reheat. We are careful with the temperature of our children’s food and have a pretty diverse diet to encompass a wider pool of nutrients so we are not concerned with some loss here and there. Microwave ovens are ubiquitous in our society and provide a safe convenience to modern life, but I don’t personally believe they should replace either the care or the art of the home-cooked meal.

Greene, Moss. “Healthy Microwave Cooking of Vegetables”. http://www.bellaonline.com/articles/art52758.asp. Retrieved 2011-Jul-23.

Jiménez-Monreal et al. ”Influence of Cooking Methods on Antioxidant Activity of Vegetables“. Journal of Food Science, 2009; 74 (3): H97 DOI: 10.1111/j.1750-3841.2009.01091.x

Lassen, Anne; Ovesen, Lars (1 January 1995). “Nutritional effects of microwave cooking”. Nutrition & Food Science 95 (4): 8–10. doi:10.1108/00346659510088654.

“Microwave cooking and nutrition”. Family Health Guide. Harvard Medical School. http://www.health.harvard.edu/fhg/updates/Microwave-cooking-and-nutrition.shtml. Retrieved 2011-July-23.

O’Connor, Anahad (October 17, 2006). “The Claim: Microwave Ovens Kill Nutrients in Food”. The New York Times. http://www.nytimes.com/2006/10/17/health/17real.html.

M. A. Osinboyejo, L. T. Walker, S. Ogutu, and M. Verghese. “Effects of microwave blanching vs. boiling water blanching on retention of selected water-soluble vitamins in turnip greens using HPLC”. National Center for Home Food Preservation, University of Georgia. http://www.uga.edu/nchfp/papers/2003/03iftturnipgreensposter.html. Retrieved 2011-Jul-23.

Quan R, Yang C, Rubinstein S, et al. (April 1992). “Effects of microwave radiation on anti-infective factors in human milk”. Pediatrics 89 (4 Pt 1): 667–9. PMID 1557249.

Scanlan, Richard A. “Nitrosamines and Cancer“. The Linus Pauling Institute – Oregon State University. November 2000.

Fumio Watanabe, Katsuo Abe, Tomoyuki Fujita, Mashahiro Goto, Miki Hiemori, Yoshihisa Nakano (January 1998). “Effects of Microwave Heating on the Loss of Vitamin B(12) in Foods”. J. Agric. Food Chem. 46 (1): 206–210. doi:10.1021/jf970670x. PMID 10554220. http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/1998/46/i01/abs/jf970670x.html.