Microwaves use low frequency electromagnetic radiation (same as in lightbulbs and radios).
When you put food inside a microwave, it absorbs these microwaves, which makes water molecules in the food vibrate, causing friction that heats up the food. Humans absorb electromagnetic waves, too. But microwave ovens produce relatively low frequency waves and they are contained inside the microwave.
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When used correctly, there’s nothing to worry about in terms of a microwave’s radiation, according to the World Health Organization.
But other concerns are less clear: for example, whether microwaving food causes nutrient loss, or whether heating food in plastic can trigger hormone disruption.
There’s no simple answer as to whether microwaving vegetables will retain more nutrients that any other method, because each food is different in terms of the texture and nutrients they contain.
Studies show that shorter cooking times tend to not compromise nutritional content. Steaming and microwaving could even increase content of most flavonoids, which are compounds linked to reduced risk of heart disease.
Food is most nutritious at the point of harvest. After that, fresh produce starts degrading.
Once picked, that fruit or veg is using its own nutrients to keep its cells alive. Vitamin C found in produce is also sensitive to oxygen and light.
An adjective that can whet our appetites is "natural", while we tend to associate "processed" food with long lists of ingredients we can't pronounce.
Actually, naturalness doesn't automatically mean a food is healthy, says Christina Sadler, manager at the European Food Information Council and researcher at the University of Surrey.