What does a microwave do to your food?
Microwave ovens are fast, convenient and easy to use. Like every cooking method, microwave heating can change the nutrient content of food. The amount lost depends on factors such as temperature, cooking time, the amount of water used and the particular nutrient.
The original version of this article cited Dr. Ed Bauman and several studies reporting losses of particular nutrients in vegetables and proteins after microwave cooking. It also referred to research on asparagus, garlic and broccoli. Those findings should not be interpreted as evidence that microwave cooking generally destroys nutrients more than other cooking methods.
Cooking method matters
Heat-sensitive vitamins such as vitamin C can decline during cooking, regardless of whether the heat comes from a microwave, boiling, roasting or another method. Because microwave cooking is often relatively quick and can use little water, it can in some cases preserve nutrients as well as—or better than—longer cooking methods.
Garlic is a useful example of why preparation matters. Crushing or chopping garlic activates the enzyme alliinase, while heating can reduce its activity. Allowing chopped garlic to stand briefly before cooking may therefore affect the formation of some sulfur compounds.
What about broccoli and antioxidants?
Individual studies have reported large changes in particular antioxidant compounds under specific microwave conditions. However, the result depends strongly on cooking time, power, water and the compound being measured. A single percentage should therefore not be treated as a universal effect of microwave cooking.
Breast milk
Microwaving breast milk is generally discouraged. Uneven heating can create hot spots that may burn a baby's mouth, and excessive heating can damage some of the milk's beneficial components. Follow recognised infant-feeding guidance for safely warming expressed breast milk.
Use microwave-safe containers
Avoid heating food in plastic containers unless they are specifically labelled microwave-safe. Heat can increase migration of substances from unsuitable plastics into food, especially with fatty foods. Glass and ceramic containers designed for food heating are straightforward alternatives.
Do microwaves create dangerous food?
Microwave ovens use non-ionising electromagnetic radiation to make water and other polar molecules in food move and generate heat. Properly functioning microwave ovens do not make food radioactive. Claims that ordinary microwave cooking creates uniquely dangerous “radiolytic compounds” are not supported by established food-safety evidence.
Bottom line: microwave cooking can reduce some nutrients, just as other forms of cooking can, but it can also preserve nutrients well because cooking times are short and little water may be required. Fresh, steamed and microwaved vegetables can all form part of a healthy diet. The most important practical points are not to overcook food and to use suitable containers.