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Foods that You Should Never Reheat in a Microwave

We already know better than to nuke plastic—or heaven forbid, aluminum foil—but certain foods can become downright toxic when blasted in the microwave. Here's what you need to know.


Some 30 years ago, American kitchens received the gift of the microwave and quickly became dependent on it for lightning-fast heating. Younger generations can’t even imagine making oatmeal, hot chocolate, or popcorn without it. And yet so many of us are using the microwave incorrectly. Sure, we know to never zap aluminum foil, metal, or plastic, but there are equally dangerous risks involved in reheating certain foods.

For starters, a microwave does not cook food evenly, which often means any bacteria present in the food will survive. Then there’s the problem of microwave blasts directly contributing to the production of carcinogenic toxins. To minimize the microwave risks, resist the urge to use to cook or warm these six foods:

1. Hard-boiled eggs: Shelled or unshelled, when a hard-boiled egg is cooked in a microwave, the moisture inside creates an extreme steam buildup, like a miniature pressure cooker, to the point where the egg can explode! Even scarier, the egg won’t burst inside the microwave while it’s being heated, but afterward, which means the scalding hot egg can erupt in your hand, on your plate, or even in your mouth. To avoid turning your egg into a steam-bomb, cut it into small pieces before reheating, or better yet, avoid putting it in the microwave all together.

2. Breast milk: Many new mothers freeze and store their breast milk for later use, which is great, as long as it’s not reheated in a microwave. In the same way that microwaves heat plates of food unevenly, they can also warm a bottle of breast milk unevenly, creating “hot spots” that can severely burn a baby’s mouth and throat. Then there’s the carcinogen hazard that comes with reheating plastic. The FDA recommends that breast milk and formula be thawed and reheated in a pot on the stove, or using a hot tap water. As a workaround, you could heat a cup of water in the microwave and then drop the bag or bottle of breast milk in it to thaw.

3. Processed meat: Processed meats contain chemicals and preservatives that extend their shelf lives. Unfortunately, microwaving them can make those substances worse for your health. Reheating processed meats with a burst of microwave radiation contributes to the formation of cholesterol oxidation products (COPs), which have been known to be more damaging to arteries than pure cholesterol. COPs are also directly linked to the development of coronary heart disease. Compared to other meal-prep methods, microwaving processed meats is far more likely to introduce COPs into your diet.

4. Rice: Rice, really? Apparently, microwaving rice can easily lead to food poisoning, according to the Food Standards Agency. Uncooked rice contains spores of bacteria that can survive being reheated. Once the rice is taken out of the microwave and left at room temperature, the spores could multiply and cause diarrhea and vomiting.


5. Chicken: All poultry, including chicken, contains some salmonella contamination, so it’s necessary to thoroughly cook chicken to eliminate all present bacteria. Since microwaves don’t fully or evenly cook all parts of the meat, you’re more likely to be left with surviving bacteria, such as salmonella. What’s more, chicken has a very high protein density, and it’s important for the proteins to be broken down at the same temperature. When some reheated proteins are broken down more slowly or quickly than others in the same piece, you’ll likely get an upset stomach.

6. Leafy greens: No matter how much you want to save your celery, kale, or spinach to eat later as leftovers, it’s better to throw them out than reheat them in a microwave, because the high concentrates of nitrates in leafy greens turn toxic when reheated. When blasted in the microwave, naturally occuring nitrates become nitrosamines, which are carcinogenic. The same holds true for reheating nitrate-rich beets and turnips!


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