Despite what you might read on the Internet, microwaving your food does not "kill" nutrients. In fact, it can make certain nutrients more available to your body, the SHAPE magazine reported.
In terms of the impact on your food's nutrients, microwaving is the equivalent of sautéing or heating up in a pan.
Research on this topic shows that whenever you cook greens, some of the B vitamins and other water-soluble vitamins are lost.
The amount you lose depends on the duration and rigor in which the food is cooked--steaming broccoli in the microwave for 90 seconds is a lot different than nuking it for five minutes. Another example: Sautéing green beans in a pan allows for much better vitamin retention than if you were to boil them.