Ask Umbra: Does microwaving vegetables zap their nutritional value?
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Q. Dear Umbra,
Have there been any studies done on the nutrient value of food that has been cooked via microwave, oven, or stovetop? For example: broccoli? Someone said microwaves destroy 90 percent of the nutrients in the food, versus steaming on the top of the stove where the loss is only 10 percent. We have been going back to basic, non-processed food that we grow ourselves. I usually only use the microwave to defrost or reheat … but am I reducing the food value?
The Farmer’s Wife
A. Dearest FW,
It looks like Cotati is in the midst of an interesting downtown revitalization debate. This has nothing to do with your vegetables, but it has a lot to do with the nutrient value of your daily life. I like to see cities thinking hard about how and where they grow.
I also like to see people thinking hard about how and what they eat — so a tip of the asparagus to you, my dear, for shifting your diet away from processed foods. I hope it is giving you more daily energy and leaving more money in your pocket, just as it should.
The fact is that cooking vegetables will lead to some amount of nutrient loss, no matter the method. This is why people are fans of raw food and its crunchtastic health benefits. But obviously some vegetables do not lend themselves to this approach (raw rutabaga, yum!). So let’s look at your options.
Three main factors affect nutrient loss during cooking: temperature, time, and — this is the big one — water. Nutrients tend to be both heat-intolerant and water-soluble. (How can something so good for us be so weak in the face of these basic enemies?) This means a vegetable cooked for a long time at a high temperature in a lot of water is going to lose more nutrients, so boiling, for instance, is out. But a vegetable cooked for a short time at a lower temperature in little or no water is going to lose fewer nutrients. And guess what appliance accomplishes that feat? Ye olde microwave.
Still, there are delicate nuances to this nutritional equation. For instance, your friend was right about the broccoli, sort of: Back in 2003, a study from Spain showed that steaming broccoli in the microwave caused it to lose up to 97 percent of its antioxidants, which can help fight diseases, including cancer. When the broccoli was steamed on the stovetop, only 11 percent of those antioxidants snuck away. This led a lot of people to conclude (helped along by ever-eager headline-writers) that microwaving is inherently bad. Au contraire, ma sous chef: As critics pointed out, the study used more water in the microwave than necessary, skewing the results. Says the Food and Drug Administration, “In fact, foods cooked in a microwave oven may keep more of their vitamins and minerals, because microwave ovens can cook more quickly and without adding water.”
You see how water keeps coming up? It is the real player here. Steaming, for instance, is a fairly good option because the veggies have less contact with water. Even better: Cook your veggies in a stew or soup, and you’ll be able to slurp those escapee nutrients up. Stovetop stir-frying or sautéing is also a good choice, assuming you don’t go crazy with the oil. Baking and roasting are yummy, but don’t forget that long exposures to heat will zap some of the nutrients — and here I start to get a bit twitchy about energy use.
Because, as it happens, your microwave is rather energy-efficient: It can save as much as 80 percent of the energy used by an oven, and generally beats out stovetops too. Another point in the microwave’s favor.
That said, I’m not a huge fan of microwaves. Too much talk of magnetrons makes me feel like the unknowing victim in a sci-fi film. So my advice boils down to something even simpler: Keep eating your vegetables. Cook them however you and your family will enjoy them most. Buy local, buy organic when you can, and spend a little time in this boringly named but secretly interesting vegetable nutrition database to get more specifics on how to select, store, and prepare every variety your heart desires.
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