Reheating certain foods can change the chemical component and render them seriously poisonous
Either toss the leftovers out or eat it cold. Spinach contains a high quantity of nitrates. They are a good supply of iron until you reheat them which makes them increasingly carcinogenic and toxic to your system.
Leaving cooked potatoes out at room temperature for any length of time, or reheating them, will promote the growth of a rare bacteria called botulism. Rather refrigerate cooked uneaten potatoes immediately. Pack them in ziplock bags and put in the fridge straight away … Don’t wait for them to cool down.
Celery and carrots
These have the same dangers as spinach. When possible, remove the cooked carrots and celery from a dish that you are reheating.
Like potatoes, don’t leave rice out at room temperature or reheat. It develops poisonous spores which multiply faster in room temperature or an oven. Again, store cooked rice immediately in a sealed container after being cooked.
They are potentially the most dangerous of the lot. Reheating cooked mushrooms can cause severe stomach complaints.
Reheating any form of cooked eggs can cause serious sickness, playing havoc with your digestive system. The very idea of reheating cooked eggs is pretty repellant.