I am as certain that microwave ovens are harmless as modern physics allows one to be…because I know how they work, as much as modern physics has determined.
First, it’s silly to confuse microwave “radiation” with bad, atomic “radiation” that causes mutations, et cetera…they are two unrelated things. Microwaves, like the light and television signals filling the air around you, are actually WAVES, as the name implies. Bad “radiation” is comprised of particles, that can hit the atoms in your body and impart energy to them, harming you. Waves simply can’t do that.
But even fear of the bad, particle radiation hitting your food is misplaced. When they sterilize food with the harmful radiation, it’s not in a way that allows radiation to be “picked up”, so the food is not radioactive afterward. And, incidentally, the same is doubly true of food in a microwave oven.
What microwave ovens actually do is present waves that are a frequency somewhat near the natural harmonic for water. This causes the water (and other) molecules in the food to be flipped upside down and back, as the waves pass through them.
THAT IS ALL IT DOES.
The atoms are flipped upside down, then back. How, precisely, is that going to cause any harm, other than the energy it imparts, that manifests as heat?
See, many kinds of atoms in food, especially in water, have magnetic poles. They are “dielectric”. As the waves pass them, the magnetic polarity of the wave aligns the atom’s poles with it. As the wave goes up and down, it flips the atom up and down. That flipping is energy the atom keeps as momentum…as the movement we call “heat”.
This simple moving of atoms can’t possibly make food radioactive, other than in the sense that heat is radiation.
So you’re not going to have any more loss of nutrition, or any radioactivity, or anything else, any more than by using a conventional oven, convection oven, boiling, et cetera.
Note that the junk science article someone linked to cites a study that did not follow even the basic scientific method. They did not propose a way that microwave energy would make food less nutritious, then carry out a test pretty certain to prove that way false, if it’s false. Instead, they just fed stuff to people and tried to measure the results, without any way of determining what actual factors caused any results they found.
For example, was the microwaved food less tasty? Maybe the actual scientific evidence here is that the stress of eating yucky food causes…what did they call it? Oh yeah…degeneration in humans. Not the simple flipping of poles by waves that are much akin to light.