Lead researcher Xianli Wu, a scientist at the Beltsville Human Nutrition Research Center at the US Department of Agriculture, says there isn’t one agreed mechanism to explain why microwaving could increase flavonoid content. It could be that microwaving makes flavonoids easier to measure – perhaps by softening the plant tissue, making them easier to extract – rather than increasing their amount
But there’s no straightforward answer as to whether microwaving vegetables will retain more nutrients that any other method. That’s because each food is different in terms of the texture and nutrients they contain, according to Wu.
“Though in general microwaving is a preferred method, the optimum time will be different for different vegetables,” Wu says. “When considering commonly used domestic cooking methods, microwaving is a preferred cooking method, at least for many plant foods, but probably not for every plant food.”
In another study, researchers compared the content of phenolics (compounds associated with various health benefits) of various vegetables after being boiled, steamed and microwaved. Microwaving and steaming caused a loss in phenolic content in squash, peas and leeks, but not in spinach, peppers, broccoli or green beans. The researchers also tested for antioxidant activity.
For both measures, vegetables fared better in the microwave compared to being boiled.
“Moderate heat treatment might have been a useful tool in improving health properties of some vegetables,” the researchers write.
Heating plastic
We often microwave foods in plastic containers and wrapping, but some scientists warn of the risk of ingesting phthalates. When exposed to heat, these plastic additives can break down and leach into food.
