Despite what you may have heard, a study in the Journal of Food Composition and Analysis showed that vegetables cooked in the microwave lose very little of their nutritional value—in fact, microwaving, like steaming or stir-frying, actually helps minimize the loss of nutrients (particularly vitamins B and C) that are often lost to the cooking water when vegetables are boiled.
While some compounds such as antioxidants and phytochemicals can be destroyed by any cooking process, the review found that microwaving was particularly good for the retention of vitamin C in green beans, spinach, broccoli, peas, and corn.
If you’re still worried, as the Produce for Better Health Foundation points out, eating vegetables however you choose to prepare them (even in the form of juice) is much better than not eating them at all!