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8 Foods That May Be Cancerous when Reheated

Posted by Carmen Chu on



As we are moving towards living a more sustainable life, it’s only natural that we don’t want to waste food as well.  So we buy our good ol’ Glasslock containers, pack our foods for next day’s lunch, or do a huge grocery haul on Sundays and start meal prepping for the week.   Honestly, I commend people who can devote so much time in preparing their meals or those who really save almost every grain of rice. I guess coming from an Asian family, it was very normal to see your mom ask the waiter for several takeaway boxes and start separating the leftovers into a very organized manner (saucy dishes in one box, dry foods or white rice in the other).

But research has found that as well intended as saving food is, this can actually be quite detrimental to your health! Certain cooked ingredients, if reheated (especially if it’s been stored improperly, can make you very sick.  This is because the heat will change the chemical structure of certain foods that make it incompatible with the human digestive system.

Making you physically ill is a small issue compared to the possibility of getting cancer from the carcinogens found in reheating foods such as green leafy vegetables.  For instance, with spinach, it contains a high amount of iron. When iron is heated and reheated again, this may cause the metal to oxidize and release dangerous free radicals, known to cause cancer and infertility.  

So as you can see, even though we are doing a good thing for our planet, we might be doing a very bad thing for our own health.  

There is good news though!  Some foods are actually okay to eat the day after. But the following foods I’ll be mentioning should definitely be avoided as much as you can!

vegetables hong kong

Vegetables (Dark Green Leafies)

Vegetables are definitely super healthy and delicious but if you can’t finish it in the same meal, it’s best to just toss it.  If you really don’t want to waste it, there is one possible solution. You could eat the leftovers cold or mix it into a salad after, but it’s really best not to wait too long before consuming it again.   



When cooked potatoes are left to cool, the risk of food poisoning is greatly increased because warm temperatures promote the growth of a bacteria called botulism.  Ideally, you want to refrigerate your potatoes directly after cooking them if you do not intend on consuming them immediately.


Celery and Carrots

This rule is similar to spinach in that these two vegetables are considered high in terms of nitrate.  Nitrate itself is not toxic but when its converted into nitrite by reheating and coming into contact with bacteria in our saliva, stomach, and intestines, then it becomes harmful to our body.   



Just like potatoes, if we leave rice out room temperature after it’s been cooked, it can develop bacterial spores that may produce poisons in our body.  These spores exponentially multiples at room temperature so make sure any left over rice is properly stored and put in the fridge right after so it can be cooled down quickly.   


This is one food that is probably the most dangerous because of how vulnerable they are to microorganisms.  Mushrooms are full of protein and so the time that’s passed by letting them cool and then reheat will cause those proteins to be broken down further and release free radicals.  So, mushrooms should definitely be eaten immediately after they are prepared! If you do want to save them, don’t reheat and eat them cold! Mushrooms are great tossed into salads so you can also be making a delicious addition to your appetizers.  



Eggs and Chicken

Sure, they are a fantastic protein option full of many health benefits, but when reheated, they can cause serious sickness.   This is for the similar reason to mushrooms in that when protein is further broken down, it changes the structure to the point where our digestive system is not adept to break down this food.  Not only is our digestive system disrupted, reheating eggs and chicken can also be toxic for our bodies.

Now that you know the main culprits, it doesn’t mean you can never have leftovers again!  It also doesn’t mean that if you do eat the foods mentioned above, you will get seriously ill.


I just want you guys to be cautious about saving food overnight and reheating.  If there are certain vegetables you can avoid when meal prepping or storing away, why not make a smarter choice and pick less potentially dangerous options?

Hope you guys learned just as much as we did today! :)

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