Steaming is definitely a way better option than microwaving. Microwaved veggies are next to nutrient-free, because rather than heating the air/water surrounding the veggies, microwaves heat the water inside the cells. I believe it's a similar effect to boiling veggies, but worse, because when you boil them traditionally, not every cell comes into contact with the boiling water.
For your reading pleasure:
THURSDAY, Oct. 16, 2003 (HealthDayNews) -- Getting the necessary nutrients from vegetables may be even harder than you thought.
New research shows that different ways of preparing, storing and processing vegetables can affect how good they are for you.
Broccoli, for instance, can lose as much as 97 percent of some antioxidants, or cancer-fighting compounds, when it is zapped in the microwave.
Vegetables that are blanched before freezing (a common processing technique) can lose up to one third of their antioxidants. Frozen storage can also cause losses, albeit much smaller ones.
Two studies detailing these findings appear in the November issue of the Journal of the Science of Food and Agriculture.
The first study found that the simplest cooking method was also the worst when it came to preserving nutrients. Broccoli lost 97 percent of flavonoids, 74 percent of sinapics and 87 percent of caffeoyl-quinic derivatives (three different types of antioxidants) when it was microwaved.
When boiled the conventional way (i.e., not in a pressure-cooker), this green lost 66 percent of its flavonoids; when tossed in a pressure cooker, broccoli lost 47 percent of its caffeoyl-quinic acid derivatives.
Steamed broccoli, on the other hand, lost only 11 percent, 0 percent and 8 percent, respectively, of flavonoids, sinapics, and caffeoyl-quinic derivatives.
The advantage of steaming vs. conventional boiling is that you're "not using water directly in contact with the vegetable. The nutritional compounds don't go into the water," says Cristina Garcia-Viguera, lead author of this paper. "Once the compounds are in the water, the temperature destroys them much easier."
A microwave wreaks havoc because it heats the inside of the vegetable. That, combined with the fact that you normally use water when microwaving, causes the destruction of valuable nutrients.
Even reheating steamed broccoli in a microwave would probably have the same effect, Garcia-Viguera says, although she did not specifically examine this in her research.
The second study looked at the effects of blanching and freezing and of long-term freezer storage on more than 20 common vegetables. As it turned out, different species showed different effects from these processing techniques.
In general, dietary fiber components were not affected or even went up slightly. Mineral content, also, tended to remain stable.
On the other hand, antioxidant activity went down 20 percent to 30 percent during blanching.
Carrots, peas, and broccoli lost 30 percent of their vitamin C during blanching/freezing, while green beans lost 10 percent and spinach lost 40 percent (with an additional 30 percent lost during deep frozen storage).
Spinach also lost almost 40 percent of its potassium and 70 percent of its folic acid during blanching.