Experts have warned that reheating certain foods can alter their chemical makeup, causing digestive issues or creating harmful compounds. The study, based on food safety guidelines, found that improper temperature control can lead to food poisoning or remove essential vitamins. The list includes items that are better enjoyed cold or used in a different way to handle these leftovers. Examples include spinach and other leafy greens packed with nitrates, which can turn into nitrites when reheat them. Leftover rice can be difficult as it often contains spores of Bacillus cereus, a bacterium that can survive the initial cooking. The best way to use leftover rice is to cool it down within an hour of cooking and put it in the fridge. Cold chicken can be used for sandwiches, salads, or tacos, and uses it cold to preserve its texture. Eggs are a great way to eat them cold, but they don't do well with reheating their protein structure.