Do microwaves destroy nutrients in food?

The convenience of a microwave is hard to beat. How else can you heat leftovers from cold to hot in under a minute? But what’s the cost of that convenience? Microwaves have been blamed for causing cancer and stripping nutrients from food. So, microwave oven: a practical heat tool or a dangerous denaturing device? Let’s examine the facts.

To begin, we must understand how microwaves operate. Microwaves are powered by a magnetron, which may sound like an alien invader in a Will Smith movie, but it’s really just a device that converts electricity into short-wave energy [source: USDA Food Safety and Inspection Service]. Microwaves target water molecules in food, making them vibrate and generate heat rapidly. In essence, they just heat the food.

It’s crucial to remember that nearly all cooking methods can degrade nutrients, with each one impacting taste and nutrition differently. The primary factors in cooking are time, temperature, and moisture. Generally, nutrients are stable under heat, unless the food is submerged in water [source: Center for Science in the Public Interest]. Since most vegetables naturally contain a lot of water, you usually don’t need to add extra water when microwaving them.

So, where did the notion that microwaves destroy nutrients in food come from? A widely referenced study out of Spain found that most of the nutrients in broccoli were lost due to microwaving [source: Vallejo]. However, the researchers didn't just microwave the broccoli. They added water to the florets, which led to a significant loss of nutrients. (It also made them soggy and flavorless.)

Additional proof linking water to nutrient loss comes from a recent study that examined the impact of various cooking methods on the antioxidant levels of 20 different vegetables. It revealed that boiling and pressure cooking caused the greatest nutrient losses, while dry methods like microwaving and baking retained more [source: Jimenez-Monreal].

A 2013 review analyzing over 100 studies on the effect of cooking on vegetable nutrients found that steaming might be the best method, as long as the vegetables aren’t in contact with water or oil during the process [source: Palermo]. It seems that water, not microwaving, is to blame for the nutrient loss in microwaved food.

While there's little evidence supporting the idea that microwaves destroy nutrients in food, some studies suggest they may affect flavor. This is mostly because it’s hard to achieve crispiness in the microwave’s moist environment [source: Yeo].

Another important factor to consider with microwaves is that they don't always heat food evenly. Microwaves can only penetrate up to 1 to 1.5 inches (2.54 to 3.81 centimeters) into food, with the rest being heated by heat conduction. To ensure more even heating, stir or turn the food occasionally. Also, microwaving requires less moisture, as there’s less evaporation during the cooking process [source: USDA Food Safety and Inspection Service, American Chemistry Council].

While the microwave oven often gets a bad rap, it remains widely used, with 96 percent of American households reporting ownership [source: U.S. Census]. These appliances have undeniably impacted society with their convenience, though they are also known for producing soggy meals. Whether that’s a fair trade-off is up to personal judgment. One thing is clear, though: Microwaves are no more to blame for nutrient loss than traditional ovens.