Does microwaving kill nutrients in food? Is microwaving safe?

May 6, 2005

Dear Cecil:

We have friends who insist they won't eat microwave-cooked items and refuse to own a microwave oven, claiming it has deleterious effects on the nutritional value of food. I chuckle over their sensitivity--seems most restaurants today serve many items that are cooked rapidly using microwaves, so I'll bet our friends eat some of these foods unknowingly. My wife, however, is becoming alarmed over their queer beliefs. Please give her peace of mind. Are our friends' fears groundless, or am I the goat on this one?

Probably your friends are getting worked up over nothing, but this is one subject where you want to resist sweeping pronouncements. On its face, antimicrowave propaganda (you'll find loads of it on the Web) is none too persuasive--some of these people have yet to comprehend the crucial distinction between ionizing and nonionizing radiation. (Ionizing radiation is the nuclear, i.e., dangerous, kind, which includes X rays, gamma rays, etc; nonionizing is everything else, e.g., microwaves, not to mention light.) When you dig into the research, though, you realize the controversy isn't all hooey. On the contrary, what we've got here is one of the great coal-mine fires of science--an argument that, in this case, has been smoldering for 50 years without resolution. Unexpected recent developments, though, make me think we may get to the bottom of this pup yet.

The central issue is whether there's such a thing as a "microwave effect"--that is, whether microwaves do anything that conventional heating methods don't. The main way microwaves heat up a plate of leftovers is by causing the food molecules to vibrate--an accelerated version of what ordinary cooking does. The microwave effect, if it exists, is more mysterious and potentially a lot scarier. For example, some conjecture that certain frequencies of microwave radiation can resonate with food, body tissues, and whatnot. Just as a low-power radio wave reaching a tuned-in boom box can rattle windows, a seemingly innocuous beam of microwave energy striking a harmonically attuned target may have disruptive effects. Microwave ovens aren't the only or necessarily the most urgent cause for alarm, either. Another significant source of microwaves, admittedly of a different frequency, is the ubiquitous cell phone, which people hold for extended periods to their ears, only a few centimeters from their brains.

The mainstream response to fear of microwaves is generally: You're on crack. For years the common view among scientists has been that the microwave effect is a myth and that whatever happens in a microwave oven happens because stuff gets hot. But disquieting indications to the contrary persistently come to light. For instance, in a paper often cited by microwave foes, doctors at Stanford University (Quan et al, 1992) reported that microwaving frozen breast milk sharply reduced the potency of the natural infection-fighting agents it contained. "The adverse effects . . . are difficult to explain on the basis of hyperthermia [high heat] alone," they wrote.

Yeah, sure, whatever. But now that attitude may be shifting, in part because of that unexpected development I was telling you about: microwave ovens' finding their way out of the kitchen and into the laboratory. Scientists have long used microwave ovens to heat up their coffee just like everybody else, but in the late 1980s they came to a startling realization: The ovens could greatly accelerate useful chemical reactions, sometimes by a factor of a thousand. Processes that once took hours, days, or months could be completed in minutes, often without the toxic solvents previously required. Initially researchers used consumer-model ovens they bought at the appliance store, but soon realized what chicken potpie lovers had known for years, namely that an ordinary microwave oven is not a precision instrument and often gives unpredictable results. With burgeoning interest in "microwave chemistry" and a corresponding push to improve microwave hardware, a few big heads conceded that maybe it was time to inquire more deeply into how these things actually worked. The matter has yet to be fully elucidated, but already some think the microwave effect may not be a myth after all: "One suggestion," a bunch of chemists wrote recently, "is that this is some form of 'ponderomotive' driving force that arises when high frequency electric fields modulate ionic currents near interfaces with abrupt differences in ion mobility."

You'll excuse me if I don't translate. My point is, a lot more people who can say "ponderomotive" without blinking are now burning up the dendrites trying to figure out what microwaves do, a necessary first step in determining whether that's good or bad for those less interested in ionic currents than lunch. Granted, none of this resolves your question, mainly because we still don't have enough info to answer it with anything other than paranoid speculation or empty reassurance. But at least there's the prospect that someday we will.

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