Some people believe that microwave cooking removes nutrients and makes food less healthy.

Microwave ovens cook food using waves of energy that are similar to radio waves but shorter. These waves are remarkably selective, primarily affecting water and other molecules that are electrically asymmetrical — one end positively charged and the other negatively charged. Microwaves cause these molecules to vibrate and quickly build up thermal (heat) energy.

Some nutrients break down when they are exposed to heat, whether it is from a microwave or a regular oven. Vitamin C is perhaps the clearest example. But because microwave cooking times are shorter, cooking with a microwave does a better job of preserving vitamin C and other nutrients that break down when heated.

Cooking vegetables in water robs them of some of their nutritional value because the nutrients leach out into the cooking water. For example, boiled broccoli loses glucosinolate, the sulfur-containing compound that may give the vegetable its cancer-fighting properties (as well as the taste that many find distinctive and some find disgusting). Is steaming vegetables better? In some respects, yes. For example, steamed broccoli holds on to more glucosinolate than boiled or fried broccoli.

The cooking method that best retains nutrients is one that cooks quickly, heats food for the shortest amount of time, and uses as little liquid as possible. Microwaving meets those criteria. Using the microwave with a small amount of water essentially steams food from the inside out. That keeps more vitamins and minerals than almost any other cooking method. (Harvard News Letter)