Many of us depend on leftovers for a quick and convenient dinner.
But according to diet experts, there are some foods that you should only warm once – and should never reheat.
There’s two reasons why this is the case.
First, the chemical compounds of ingredients can change when they’re reheated, triggering the release of toxic substances linked to problems such as damage to kidneys.
Secondly, allowing some foods to cool before heating can encourage the growth of hard-to-kill bacteria such as E. coli and listeria.
In a recent video shared with her 23,000 TikTok followers, dietitian Harini Bala revealed three surprising foods you should never reheat.
First on the list is spinach.
Ms Bala said that the leafy green vegetable contains a substance called oxalic acid which is harmless when spinach is eaten in its raw form.
However, once reheated, the oxalic acid ‘crystallises’ and becomes ‘toxic’. In high doses, the substance can increase the risk of kidney stones – clusters of crystals that form in the urinary tract and can become painful.
Ms Bala added: ‘It also contains nitrates and this will get converted into nitrites when it is reheated and these are toxic.’
Nitrites are substances that are thought to combine with chemicals in the gut to form compounds which increase the risk of bowel tumours developing.
Other studies have found that spinach leaves are rife for infestations of listeria – a bug that is often responsible for foodborne illness.
Experts say that if spinach has not been properly heated, the bacteria can still live on it. This can cause fever, flu-like symptoms, headache, stiff neck, confusion and even seizures.
The next favourite to avoid reheating is tea, Ms Bala said.
Not only will it make the drink more bitter – because reheating increases the amount of tart-tasting tannins – ‘any kind of dormant bacteria can become active in it’, she said.
Finally, the riskiest food to reheat is rice, according to Ms Bala.
When cooked rice is cooled, it can contain Bacillus cereus, a spore-forming bacteria typically found in soil and vegetables.
But the spores are heat resistant – so even when you heat them up, it doesn’t eliminate the risk.
Symptoms of illness from Bacillus cereus include vomiting, diarrhoea and abdominal cramps.
There are some rules you can follow to limit the risk of contracting the bug, Ms Bala said.
‘It can be reheated if you’re storing it within two hours [after cooking it] in the fridge in an airtight container.
‘But if you’re cooking your rice in the morning [leaving it out] and storing it in the fridge at night to eat the next day, there is a huge possibility of Bacillus cereus forming.’
Last year, a story resurfaced online about a 20-year-old who died from so-called ‘fried rice syndrome’ – which also affects pasta.
The unidentified man, from Belgium, died after eating reheated spaghetti he had left out in his kitchen for five days.
He reportedly began experiencing a range of symptoms shortly after eating the pasta, including nausea, abdominal pain, a headache, diarrhoea and vomiting.
He died within 10 hours.
The post-mortem found the man had suffered moderate centrilobular liver necrosis, which had led to his organs shutting down.
Doctors who detailed the case in the Journal of Clinical Microbiology said Bacillus cereus was likely to blame.
