Microwave May Cook Benefits Out Of Veggies

BOSTON -- No matter how you slice them, vegetables are good for you -- but how you cook and store them may be another matter.

Two new studies suggest the microwave and the freezer may be foes when it comes to cancer-fighting compounds.

A study published in the Journal of the Science of Food and Agriculture found that lengthy cooking times and high temperatures greatly diminish the nutritional value of vegetables. During cooking, vitamins -- including water-soluble vitamins B and C -- will dissolve into the water and are then unknowingly thrown away after cooking.

However, research says it's not just water that's soaking out the nutrients. Time-saver techniques are also to blame.

"It takes a long time to steam them, and I lead a kind of busy schedule and life, and so ideally, I would, but I end up using the microwave for vegetables," college student Josh Benham said.

Antioxidants, which are plentiful in vegetables, are the cleanup crew for the body. They go around mopping up the free radicals that can cause cancer and heart disease.

But the study found that microwaving broccoli erases 97 percent of flavonoids, 74 percent of sinapics and 87 percent of caffeoyl-quinic derivatives -- three types of antioxidants.

"In the microwave, the nutrients came out of the broccoli and into the water, even though there was a smaller amount of water used and leached into the water, dissolved into the water and evaporated," said Stephanie Vangness, a dietician at Dana Farber Cancer Institute.

Microwaving vegetables aggressively heats their inside and causes the destruction of cancer-fighting antioxidants.

Pressure cookers and steamers are among the best ways to prepare vegetables without ridding them of their value, the study said.

The advantage of steaming over conventional boiling is that the nutritional compounds of the vegetables don't go into the water, making it harder for the nutrients to be destroyed. Vegetables steamed for only a few minutes will retain more nutrients than those boiled in water for a longer time

As a result, when steamed, broccoli lost only 11 percent, 0 percent and 8 percent, respectively, of flavonoids, sinapics, and caffeoyl-quinic derivatives.

Any cooking that minimizes the time, temperature and amount of water will help to preserve nutrients, experts said.

But it's not just how vegetables are cooked, it's how they're packaged. Another study found that some frozen vegetables can lose up to one-third of their antioxidant power.

Spinach, for example, lost 70 percent of its folic acid content in the initial blanching and freezing.

For some of the other vegetables, it took more time in the freezer to lose a significant amount of antioxidants -- from eight or 12 months to 18 months. Both the process and the length of time contributed to the decrease in nutrients.

"If you always eat spinach from a frozen cube, it's a good idea to try to occasionally eat a raw spinach salad," Vangness said. "Some of the phytochemicals are going to be better absorbed if the product is cooked while others will be better absorbed if it's raw."

Study Abstracts