Microwaves have generated a lot of debate and opposing opinions

There's nothing dangerous about microwave radiation. But is the same true for plastic containers used to heat food? Here's what the latest research says.

For decades, the microwave has been the workhorse of our kitchens, yet this household item has generated so much debate and conflicting opinions.

The microwave was called a real salvation for those who cannot and do not intend to cook, while some chefs claimed that this invention was killing the art of cooking.

But there is another eternal question, and it is not about the subtleties of culinary art: when is cooking food in a microwave harmful to health?

According to the World Health Organization, microwave radiation poses no risk when used properly. But there are other concerns, including whether microwaving food results in a loss of nutrients and whether heating food in plastic containers can cause hormonal disruption.

Lost nutrients?

Some studies suggest that vegetables lose some of their nutritional value when microwaved.

For example, broccoli can lose up to 97% of its flavonoids, phytochemicals with antimicrobial and antioxidant properties, a third more than after cooking.

However, one 2019 study indicated that previous experiments with broccoli were carried out at different temperatures, different cooking times, and did not take into account whether the product was in water.

It turns out that short cooking (when these vegetables were left in the microwave for one minute) did not destroy the nutrients. Steaming or microwaving may even increase the amount of flavonoids.

“Under the cooking conditions used in this study, microwave cooking appeared to be a better way to preserve flavonoids than steaming,” the scientists wrote.

They found that if you microwave broccoli with too much water (about the amount we use when cooking in a saucepan), the amount of flavonoids decreases.

Experts say a conventional oven could become a competitor to the microwave.

A 2020 study compared the nutritional value of frozen convenience foods cooked in a microwave oven to the same foods cooked in a conventional oven. The researchers found that the only difference between the two was that the microwaved food retained slightly more vitamin C. But the scientists didn't explain why.

There is no single explanation for why microwaving increases flavonoid levels, says Xiang Li Wu of the USDA's Beltsville Research Center.

Perhaps after microwaving they are simply easier to detect and isolate, and there is no increase in quantity here.

There is also no clear answer to the question of whether vegetables retain more nutrients after microwaving than after other cooking methods, says Xiang Li Wu.

“While the microwave is generally the best cooking tool, the optimal cooking time will vary for different vegetables,” he explains.

So even though the microwave is the best tool, it's far from being the best for all plant-based foods.

In another study, scientists compared the content of phenols (compounds that act as antioxidants and have many health benefits) in various vegetables after boiling, steaming, and microwaving.

Microwaving and steaming reduced the phenolic content of pumpkins, peas, and leeks, but not spinach, peppers, broccoli, or green beans. The researchers also tested antioxidant activity.

It turned out that the best indicators were not those that were boiled, but those that were processed in a microwave oven.

A recent study from 2023 also showed good results for microwaving. Scientists compared the effects of boiling, steaming, and microwaving various vegetables and concluded that microwaving was the most effective at preserving nutrients.

Overheated plastic?

We often microwave food in plastic containers or packaging. Scientists warn about the risk of inhaling phthalates (phthalic acid esters, which are used in the production of plastic dishes and packaging - Ed .).

During high-temperature processing, these toxic additives can break down and leach into the food.

“Some types of plastic are not intended for use in microwave ovens because they are made of polymers that melt when heated, and when the temperature exceeds 100 degrees Celsius, they can leach into food,” says Jumin Tan, a professor of food engineering at Washington State University.

In a 2011 study, scientists bought over 400 plastic food containers and found that most of them released chemicals that disrupt hormone function in the human body.

Phthalates are the most common additives that make plastics more flexible. They are often found in food containers, plastic wrap, and water bottles. Phthalates have been shown to disrupt hormones and our metabolic system.

In children, phthalates can increase blood pressure and insulin resistance, which increases the risk of metabolic diseases such as diabetes and hypertension. Phthalate exposure has also been linked to infertility, asthma, and attention deficit disorder.

Phthalates are also potential disruptors of thyroid hormones, notes Leonardo Trasande, a professor at New York University School of Medicine. These hormones, among other things, are crucial for a baby's brain development during pregnancy.

Bisphenol A is also a common component of plastic products, and research suggests that it can disrupt hormone function in humans. A 2020 study suggests that bisphenol A, which can enter the body through food, can disrupt cell behavior and block the action of natural hormones by binding to their receptors inside cells. This can lead to cancer, hormonal disruptions, fertility problems, and can affect our immune system, according to researchers.

But there are few such studies compared to those studying the effects of phthalates.

Phthalates are everywhere, from toys to body lotions, and it's still not entirely clear how much harm they cause. But most experts agree that heating food in a plastic container containing phthalates can increase their effects on the human body.

“Microwave heating activates contaminants,” says Professor Rolf Halden, director of the Biodesign Center at Arizona State University. “This process is used in laboratories to isolate contaminants from samples before they can be analyzed for chemical composition.”.

However, as Trasande points out, the level of potential risk does not necessarily depend on how often a person heats up food in a plastic container. The relationship here is nonlinear.

“We now know from numerous studies that low levels of exposure can be the most dangerous. And there is no level that can be called safe,” he says.

"It's important to remember that when a plastic container heats up, the danger comes from those surfaces that don't come into contact with the food. For example, moisture can condense on the lid, which contains harmful substances, which then get into the food in the form of droplets," emphasizes Halden.

The best way to minimize risks is to use ceramic containers instead of plastic ones. If you use plastic, avoid using containers that are deformed, as old and damaged containers are more likely to leach chemicals.

You should also check the labeling on the container itself: those with the number 3 and the letters “V” or “PVC” contain phthalates.

Temperature risks?

But even if you give up plastic utensils, other potential health hazards remain: for example, uneven heating of food and the high temperatures used in the microwave.

Try using the microwave not for cooking (since food can heat unevenly in it - and, accordingly, some parts of the dish will be less cooked), but for reheating already cooked food.

“Depending on the size of the portion, some parts of the food may heat up more than others,” says Francisco Díaz-Gonzalez, a professor at the University of Georgia (USA). “In a cross-section of a product, the temperature of its different layers may differ. It is difficult to achieve absolutely uniform heating, especially when it comes to a dish made from raw products.”.

However, it is important to note that reheating also carries risks. Food should be reheated until it reaches a temperature of 82 degrees Celsius, which kills all harmful bacteria.

But every time food cools down, these bacteria are especially active, and the next time you reheat it, it will be harder to get rid of them. Therefore, it is not a good idea to reheat food more than once.

High temperatures in the microwave can also pose some risk. However, the problem is not the temperature itself. Some studies have shown that there is a risk when cooking starchy foods, including grains and root vegetables.

When Betty Schwartz, a professor at the Hebrew University of Jerusalem, saw her students heating up jacket potatoes in the microwave during their lunch break, she noticed small crystals forming in the potatoes.

Upon examining them, she discovered that these crystals contained high levels of acrylamide, a chemical used in polymer production and considered toxic. In this case, the acrylamide was a byproduct of cooking potatoes.

Schwartz asked students to cook potatoes and found that no acrylamide formed after cooking. She concluded that the high temperature of the microwave was the cause.

This is concerning because animal studies have shown that acrylamide acts as a carcinogen by interfering with the DNA of cells. There is little evidence that it does the same in humans.

There is some research that suggests that microwaving food contributes more to the formation of acrylamide than other methods.

However, researchers also found that brief microwave exposure—such as blanching or defrosting—at low power can limit acrylamide formation during subsequent cooking.

“At 100°C, enough energy is released to change the bonds between molecules and create a molecule that can react with DNA, causing mutations,” says Schwartz. “When there are a lot of mutations, cancer can occur.”.

Animal studies have shown this to be the case for acrylamides.

One way to get around this is to soak the potatoes in water before putting them in the microwave.

Dangerous radiation?

As for the radiation in a microwave oven, it is completely harmless. These devices operate on low-frequency electromagnetic radiation, similar to that used in light bulbs and radios.

Food placed in a microwave oven absorbs these microwaves, which causes the water molecules in the food to vibrate, creating friction and thereby heating it.

Humans are also capable of absorbing electromagnetic waves. But microwave ovens produce relatively low-frequency waves that do not travel beyond the appliance.

Even if they did, these waves are safe, says Professor Tan. (But of course, the high temperatures in a microwave are not safe at all, so you should never try to put a living thing in there!)

“We are exposed to waves like those in microwave ovens every day. People even exchange radiation with each other,” says Jumin Tan. “If you eat foods made from grains grown in the sun, you don’t have to worry about microwaved food.”.

Unlike X-rays, microwaves do not use ionizing radiation, which means they do not have enough energy to detach electrons from atoms.

“To damage DNA, you need to break chemical bonds. This is the main way radiation kills: cells begin to mutate, and cancer develops,” explains Timothy Jorgensen, associate professor of radiation medicine at Georgetown University Medical Center (USA).

According to him, all concerns about microwave radiation were dispelled in the first years after the invention of the microwave oven.

In particular, scientists from the Military Research Center at the US Department of Defense have conducted a lot of research on the safety of microwaves. And this has largely dispelled fears.

The microwave has long been recognized as a safe kitchen appliance, but, as modern research shows, there are caveats. There are some points to pay attention to.

And experts in particular continue to worry about how the plastic packaging we use to microwave food can affect our hormones – and consequently our overall health.