Microwave ovens have been in existent in almost every American home for 60 years now. It has been a household name for the longest time, in spite of the convenience it gives, some people still have doubts that cooking food with microwaves somehow makes food less nutritious.
According to HuffPost Science, microwaved foods may be more nutritious. As Dr. Guy Crosby, an adjunct associate professor of nutrition at the Harvard School of Public Health in Boston explained in an email, "In general, microwaving results in less loss of nutrients compared with boiling and frying, because it is a dry method of heating (so water soluble nutrients like many B vitamins and vitamin C are not leached out of the food) and because it is very rapid, so nutrients are exposed to the heat generated by the microwaves for much less time."
This is further explained in an article from Harvard Health Publication (HHP) website,
"Microwave ovens cook food using waves of energy that are similar to radio waves but shorter. Some nutrients break down when they're 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."
Heat actually breaks down some nutrients for the very fact that cooking can damage their chemical structure -- and the longer time the food cooks, the more nutrients tend to break down. "Any process that heats a food (microwaving, baking, boiling, frying, etc.) reduces the level of heat sensitive vitamins. The details depend on the time and temperature and the specific vitamin," added Dr. Don Schaffner an extension specialist in food science and professor at Rutgers University in New Jersey.
As for the best cooking method so as to lock in the nutrition in meals, experts from Harvard say that the method that uses heat for the shortest amount of time with less liquid is the most healthy way of cooking foods, and microwave meet those criteria. But when cooking vegetables, steaming is may be the best method according to Dr. Crosby.