I frequently microwave my food since I prefer not to spend more than 30 minutes for food prep and eating, total.
The problem is that different nutrients react in different ways: some do worse with more heat, some with more contact with water, some the length of time is less important than the absolute temperature (or vice versa), cooking with fat might help or hinder... Also the reason why these studies often contradict each other is, I assume, that individual cooking methods are highly subjective. It doesn't matter that baking is better than boiling, if a food that you'd boil for 5 minutes you'd blast in the oven for an hour before eating it.
That said this is one of the best studies (in that it actually tests a variety of methods and foods). It finds that: "griddling, microwave cooking, and baking alternately produce the lowest losses, while pressure-cooking and boiling lead to the greatest losses; frying occupies an intermediate position" also "green bean, celery, and carrot" became more nutritious after all methods, whereas most vegetables became less.
This (2) study suggests that microwaving is often better than conventional methods for "thiamin, riboflavin, pyridoxine, folacin, and ascorbic acid" using low power. This (3) review simply reports that the differences are minimal.
My general understanding is that the microwave doesn't actually change the nutritional content or damage the nutrients themselves, but it destroys valuable enzymes that contribute to digestion and general gut health. What was once living is now dead.
If you're going to do it, then at least use a ceramic or glass container and not a plastic one!
From what I've read, microwaving actually preserves the nutrients in vegetables better than any other method. Steaming and sauteeing are next best. Boiling is the worst (since you're just making vitamin water in that case) but blanching (a boiling-based method) is effective at preserving nutrients.
I wish I could find a good study on this. This seems like something where the research should be easy and definitive. Just prepare some vegetables using various methods then analyze the nutrient content. Unfortunately, the information I've seen on this has been lacking citiations and from the usual nutritional 'experts' that we've learned to ignore...
Regarding foods other than vegetables, I have no clue!
I don't have a definitive answer, but out of caution due to the unknown I limit the use of the microwave whenever possible. It isn't that hard to warm up food on the stove, and life still feels relatively easy. :-P
Here's an intriguing article against microwave use that should at least give one pause: http://findarticles.com/p/articles/mi_m0ISW/is_2001_June/ai_75178712/
Guess my paleo sisters could not have even imagined such craziness. why even bother with it...so they can find in 25 years what it really was doing to our food. Take some time and prepare your food with a flame from the gas stove :) Part of living is enjoying...being in joy.
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