The Microwave Myth

3 min read

Many times when I microwave my food, I get told I shouldn’t do that because it destroys the nutrients in the food. Recently I made some chilli con carne for a friend and the topic of microwaving came up. Even though I told her about the safety of microwaving food, after all I had just completed my degree in nutrition, her response was “Yeah I know, but the microwaves have got to go somewhere, and they can’t be good for you.”

Let’s break this down. Firstly, we need to talk about the type of radiation that microwaves emit, non-ionising radiation, and we need to understand how this differs to ionising radiation. Ionising radiation is the form of radiation associated with cancer. In short, this type of radiation can knock electrons away from atoms or molecules, allowing highly reactive free radicals to wreak damage on adjacent organic matter. In the case of cancer, the damage is caused to DNA or proteins involved in DNA replication, which can lead to uncontrolled division of cells, leading to tumours. Non-ionising radiation from microwaves only have enough energy to excite atoms and molecules in food, causing electrons to move into a higher energy state. This has a thermogenic effect – in other words it heats your food. Whilst microwaves can be damaging to us and potentially carcinogenic if microwaves pass through the human body, the same way it can be damaging if you were cooked in the oven or burned by the sun, eating food heated by microwaves will do you no harm. There is no evidence that microwaves are harmful when used for heating food. Just don’t go sticking your hand in one or leaving the door open whilst it’s running. Common sense. Hopefully.

Do microwaves destroy the nutrients in food? The answer to this isn’t so straightforward. When looking at the effect microwaving has on the nutrient content of vegetables, studies have found that this depends on the vegetable, and various microwave parameters including the duration of cooking, wattage, if water is used or not, and the volume of water used. When water was used when microwaving broccoli, researchers observed losses of vitamin C, and they concluded that shorter cooking times with the least amount of water led to the least vitamin C loss. This was supported by Tabart et al (2018), who found that availability of vitamin C increased proportionally with cooking power and reduction of cooking time. However, they also found that 40% of anthocyanins were lost once the cooking power was increased. Zhang and Hamauzu (2004), found comparable nutrient losses with boiling, however the researchers chose to use the same amount of water (200ml) when microwaving, essentially boiling the broccoli, but in the microwave. Conversely Tabart et al (2018) who microwaved broccoli and red cabbage without adding water, observed an increase of vitamin C content after microwaving, and a greater number of anthocyanins were retained through microwaving compared to boiling, steaming. Similar results were obtained by Volden et al (2009). Pellegrini et al (2010) determined microwaving to be the best method for retention of glucosinolates in both fresh and frozen Brassica vegetables.

Some people follow a raw plant-based diet believing this to be the best way to eat their veggies due to the lack of processing. Eating vegetables raw is the not the best way to maximise your nutrient intake, as to release some of the beneficial compounds, the plant tissue needs to be damaged.

No cooking method retains 100% of nutrients. If water is used in any cooking method, then there will be greater losses of nutrients. Whilst steaming is often heralded as the most superior cooking method for vegetables, microwaving vegetables is just as effective, if not more so in some cases.

Time to get over your fear of the microwave.