Microwaves are a basic tool for those who do not know how to cook or are lazy. But how does it affect health?
Despite being a workhorse in the kitchen for decades, few household items have been more divisive than the microwave.
Those who cannot or do not want to cook consider it a salvation, while some chefs believe that it is capable of ending the art of cooking.
However, there is another debate beyond this culinary dispute: when is microwave cooking bad for your health?
If used correctly, there is nothing worrying about microwave radiation , according to the World Health Organization.
But the answer to other concerns about this way of cooking is not so obvious, including whether microwaved food loses nutrients or heating food in plastic containers can interfere with our hormones.
Some research has shown that plant loses n some of its nutritional value in the microwave.
For example, 97% of flavonoids – the plant compounds that have anti-inflammatory benefits – were found to be lost in broccoli.
The loss or increase of nutritional value will also depend on the cooking time.
That’s a third more damage than boiling causes.
However, a 2019 study examining nutrient loss in broccoli in the microwave noted that previous studies varied in cooking time, temperature, and whether or not broccoli was in water.
Research found that shorter cooking times (microwaving broccoli in the microwave for one minute) did not compromise its nutritional content.
Steam and microwave cooking could even increase the content of most flavonoids, which are compounds linked to reducing cardiac risk.
“Under the cooking conditions used in this study, microwave cooking was shown to be better at preserving flavonoids compared to steam cooking,” the researchers wrote.
They also found that cooking in the microwave with plenty of water (the same amount that one uses to boil) caused a reduction in flavonoids.
They decrease with one method, they increase with another
Xianli Wu, principal investigator and scientist at the US Department of Agriculture’s Beltsville Human Nutrition Research Center, says there is no agreement on a mechanism to explain why microwave cooking can increase flavonoid content.
Microwave cooking may make measuring flavonoids easier. Perhaps by softening the tissue of the plant it is easier to extract them (rather than increase their quantity).
But there is no simple answer to whether microwaving your vegetables will retain more nutrients than any other method.
That’s because each food is different in terms of texture and nutritional content , according to Wu.
“Although microwave cooking is generally preferred, the optimal time will be different for each vegetable,” says Wu.
“When you consider common household cooking methods, the microwave is the method of choice, at least for many vegetables, but probably not for all.”
In another study, researchers compared the content of phenolics , (compounds associated with various health benefits) in various vegetables after they have been boiled, steamed, or microwaved.
The last two methods caused a loss in the phenolic content in pumpkins, peas, and leeks, but not in spinach, peppers, broccoli, or beans.
They also evaluated antioxidant activity.
In both measurements, the results of the vegetables were better when microwaved than when they were boiled.
Heat in plastic containers
We often microwave food in plastic containers and wrappers, but some scientists warn of the risk of ingesting phthalates.
When exposed to heat, these plastic additives can break down and penetrate food.
“Some plastics are not designed for microwaves because they contain polymers to make them soft and flexible, which melt at low temperatures and can leak during microwave cooking if the temperature exceeds 100 ° C,” says Juming Tang, professor of food engineering at Washington State University, USA.
In a 2011 study, researchers bought more than 400 plastic containers designed for food, and found that most lost chemicals that interfere with hormones.
Phthalates are one of the compounds most commonly added to plastics to make them more flexible, and are often found in takeout containers, wrappers, and water bottles.
They were found to interfere with our hormones and metabolic system.
In children, phthalates can increase blood pressure and insulin resistance , which can increase the risk of metabolic disorders such as diabetes and hypertension.
Exposure to these substances has also been linked to fertility problems , asthma, and attention deficit hyperactivity disorder.
Phthalates are also potential thyroid hormone disruptors , says professor of environmental medicine and population health at the NYU School of Medicine in New York.
Among other things, these hormones are crucial for the development of the baby’s brain during pregnancy.
Bisphenol (BPA) is commonly used in plastic products, and studies indicate that it can also interfere with hormones. But the studies are limited, in relation to the quantity that exists on the phthalates.
Phthalates are everywhere – even in toys and body creams – and it’s still unclear how much damage they do.
But most experts agree that heating plastics with phthalates can increase our exposure to them.
“The microwave s mobilizes pollutants, ” says Rolf Halden, professor and director of the Center for Biodesign for Environmental Health Engineering at Arizona State University.
“This process is used in laboratories to extract contaminants from samples, before doing chemical analysis.”
And the potential risks don’t necessarily increase based on how often an individual heats food in the microwave in plastic containers, Trasande argues, since the relationship between the amount of chemical exposure and the risk of hormone interference is not linear.
It is important to remember that when we heat food in a plastic container, the exposure can also take place even if the plastic does not touch the food, as in the case of a lid.
“Water rises from the food in the form of steam, and it condenses on the lid, and chemicals from the lid fall onto the food,” says Halden.
The best way to minimize risks is to use other microwave-safe materials like ceramic .
If you use plastic containers, avoid those that lose their shape , since old and damaged containers are more prone to releasing chemicals.
You can also verify that they have the universal recycling symbol, usually at the bottom of the product.
Those with the number 3 and the letter V or PVC contain phthalates.
Although you avoid plastics, there are other potential risks of microwaving food, including uneven heat distribution and the high temperatures used.
First, consider using the microwave for reheating rather than cooking , as it can cook unevenly.
“Depending on the portion of food that you heat, there will be some parts hotter than others,” explains Francisco Diez-González, professor of food security at the University of Georgia, USA.
Importantly, reheating food also has its risks. Food must be heated to 82ºC everywhere to kill harmful bacteria, and since bacteria can grow every time food gets cold, you should not reheat food more than once.
Higher microwave temperatures also pose a risk. In general, high temperatures are not a problem, but some research suggests that there is a risk associated with microwaving some starchy foods, including cereals and tubers.
Crystals in potatoes
When Betty Schwartz, a professor of nutrition science at the Hebrew University of Jerusalem, saw her students microwave the potatoes for lunch, she noticed small crystals inside the potatoes.
Upon analysis, he found that they were high in the chemical acrylamide , a natural by-product of cooking.
Schwartz asked his students to boil the pope, and found that this did not create acrylamide, which he says is formed by high microwave temperatures.
This is troubling because, in animal studies, acrylamide was found to act as a carcinogen because it interferes with the DNA of cells. Human evidence is limited.
There is some research indicating that microwaves facilitate the development of acrylamide more than other cooking methods.
“At 100ºC, there is enough energy to alter the automatic junctions between molecules to produce a molecule with much more energy, which can react with DNA, which induces mutations,” says Schwartz.
“When you have a lot of mutations, this can lead to cancer.” Animal studies have shown that this may be the case with acrylamides.
One way to avoid this problem is to dip the potatoes in water before putting them in the microwave.
Regarding radiation, microwaves are totally safe . These use low frequency electromagnetic radiation , the same type that light bulbs and radio use.
When you put food into the microwave, it absorbs these microwaves, causing the water molecules in the food to vibrate, causing friction that allows it to heat up.
Humans also absorb electromagnetic waves. But microwave ovens produce relatively low frequency waves and are contained within the apparatus.
Even if that wasn’t the case, the waves are harmless, says Tang.
Of course, heat is not, so you should never put something alive in the microwave.
“Microwaves are part of the electromagnetic waves to which we are exposed on a daily basis. When you bake bread, you are exposed to electromagnetic waves and infrared energy from the elements that generate heat from the oven. Even people exchange radioactive waves with each other, “Tang explains.
“If you’re eating crops that grow in the sun, you shouldn’t worry about food from a microwave.”
Unlike x-rays, microwaves do not use ionized radiation , which means they do not have enough energy to separate electrons from atoms.
“You have to break chemical bonds to damage DNA. This is the main way it kills radiation: It causes cells to mutate and cause cancer, “says Timothy Jorgensen, associate professor of radiation medicine at Georgetown University Medical Center in the US
Concern about microwave radiation arose in the early years of its invention, says Jorgenson.
Many of the investigations carried out by scientists at the Army Natick Research and Development Laboratories in Massachusetts, USA, calmed these fears.
When it comes to cooking food in the microwave, there is a lot to consider.
They have long been considered safe, but there are certain caveats to be made, researchers say.
And, above all, some experts still question the safety of putting plastic containers inside, which can interfere with our hormones, and consequently affect our health.
This note was originally published on BBC Future. Click here to read the original version.
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