There are some picky eaters who refuse to touch a plate of leftovers. But for the rest of us, well, it's just so easy to reheat last night's dinner in the microwave. In fact, some people cook multiple servings to save time during the week, especially when we're tired or just don't feel like cooking.
However, leftover junkies out there may want to sit down for this. Research shows that reheating some of your favorite foods can be dangerous for your health, especially if they are not stored correctly.
Here's a list of common foods that should never be reheated, and why:
#1 Root Vegetables
Celery, a mainstay in soups, stews, and stuffing, can become toxic if you reheat it, especially in the microwave. Why? Well, celery contains nitrates, and reheating at high heat or in the microwave turns those nitrates into nitrites. Nitrites are those carcinogenic compounds you've heard about related to processed meat. (1)
Turnips and beets, like celery, contain high levels of heat-sensitive nitrates. While the USDA promotes microwaving veggies to retain more nutrients, reheating these same veggies brings us back to the problem of nitrates and nitrites. are common ingredients in soups and stews. (2)
So what about those leftover soups and stews? Are they OK to reheat? Well, it's best to reheat slowly at a low temperature – on the stovetop or in the oven – and remove from heat as soon as it's warm.
#2 Mushrooms
Mushrooms should be eaten the same day that they are prepared due to their complex protein content. Reheating mushrooms can change their protein composition and present a high health risk for digestive and heart problems. If you want to eat mushrooms that were made the previous day, eat them cold! (3)
#3 Chicken
Chicken, like mushrooms, contains proteins that react negatively when reheated. When cold chicken is heated for the second time, the protein composition changes, which can lead to digestive problems. If you must reheat your chicken, make sure that it is completely cooked, and the inside is steaming hot. To use leftover chicken without having to reheat it put it in a cold salad or on a cold sandwich. (4)
#4 Spinach and Butter Lettuce
These leafy greens are so healthy when eaten raw. Cooking diminishes some of the nutrients, like vitamin C, but spinach should not be heated a second time. These leaves, like celery, contain high amounts of nitrates, which can break down and form nitrosamines due to organisms that are present. Nitrites can affect the oxygen level in the blood, become toxic and cause food poisoning when reheated. (5)
#5 Eggs
Eggs should not be repeatedly exposed to heat. Reheating eggs at high temperatures after they've been boiled or fried can make them toxic and result in problems with your digestive tract. Specifically, cooking eggs in a microwave alters the proteins. The fatty acids – the nutrient-rich yolks – also become denatured or destroyed when repeatedly exposed to heat. (6)
#6 Rice
Unless you've experienced it, you've likely never heard of leftover rice syndrome. But for those who have suffered digestive upset, this illness is very real. It isn't the rice, though, that's the problem. A very natural bacterium, Bacillus cereus, lives on rice grains and other plant foods. And it doesn't mind the heat. That means that after cooking, rice not stored properly or reheated encourages this little bugger to grow to the point of making you sick. (7)
So don't leave cooked rice out at a dinner party, or you may make your guests sick with vomiting and diarrhea.
#7 Oils
Grape seed oil, canola oil, and corn oil, among others, all have very low smoke points. Vegetable seed oils tend to become rancid when you reheat them – or heat them at all! Avoid using these types of oils for cooking, baking, or frying. Reheating oil, as they do in restaurants, can turn those fragile oils rancid, creating oxidation and free radicals. (8, 9)
#8 Potatoes
If you let potatoes sit at room temperature for an extended period of time, they can lose their nutritional value, and conditions may be right for the growth of botulism. This is another storage issue, like rice. As soon as you are done cooking your potatoes, store them in the refrigerator if they are not being eaten. (10)
If you are making a dish with either potatoes or rice, cook just the amount you need for that meal. This will help eliminate leftovers. If you still find yourself with leftovers, then use them in a cold dish you can eat the next day!
As a bonus, boiled and rapidly cooled potatoes have altered sugars that feed the beneficial bacteria in your gut. This is called resistant starch. Delicious potato salad and happy microbiome!
