Can Eating Leftovers Really Cause Food-Poisoning, Or Worse Cancer?
Weight Management

Can Eating Leftovers Really Cause Food-Poisoning, Or Worse Cancer?


5 December 2017


The meal prepping is craze one that has exploded all over social media. But what is meal prep? In essence, meal prepping helps you portion out your daily food and can help people in maintaining a healthy weight. Find out what leftovers and meal prepping is all about and whether claims of major health issues arising from them are true or merely myths. 

How Can It Help?

Did you know? Studies have shown that people who practice meal prep were less likely to be overweight. This is because people who spend more time preparing meals are more likely to have healthier diets, according to a 2014 study (1) published in the American Journal of Preventive Medicine.

More recently, a 2017 study (2) of 40,000 adults in France found that people who meal prep at least a few days at a time were less likely to be overweight and stuck more closely to nutritional guidelines.

Is Overnight Food Safe To Eat?

Although meal prepping seems like a proven plan to help people stay on a healthy diet, some of us may have been told by our mothers or grandmothers that it is always good to prepare and eat fresh meals.

This idea may be the cause of some scepticism when it comes to meal prep as some may wonder whether food left overnight is still safe and nutritious to consume.

To set your worries aside, the answer is YES, overnight food is safe to eat, but only when you handle it properly. You might have the healthiest ingredients but if it not handled properly, you risk the chance of exposing yourself to unwanted bacteria that can lead to food poisoning.

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But there’s no reason to worry because learning how to store foods properly doesn’t have to be as difficult as it seems. Here are a few tips when is comes to dealing with overnight food:

#1 Distinguish Between “Meal Prep Meals” And “Leftovers”

Get rid of the idea that meal prep is synonymous to leftovers! The dictionary definition of a leftover is “something, especially food, remaining after the rest has been used or consumed”. This is also called “residue”, “scraps”, “remains” etc.

While it is true that leftovers may be contaminated with harmful organisms due to the exposure of the “danger zone” (room temperature for more than 2 hours), meal prepping is very different.

With make now and eat later meal preparation, the intention is to prepare the food in advance and store it first without consumption. Therefore, each portion is not the scraps of a previous meal, but a new meal that has been specifically created beforehand!

#2 Avoid The Danger Zone: Always Follow The “2-Hour-Rule”

Fact — According to food safety experts: potentially hazardous food that has stayed in the temperature “danger zone” 40°F – 140°F (4°C – 60°C), for more than 2 hours should be discarded. (Note: This is the FDA’s rule. Different organisation may have variations on it.)

This is applicable to perishable foods like meat, dairy, unshelled eggs and shelled eggs, most cooked food and so on. If the food has been at room temperature for more than 2 hours, then perhaps you should discard it.

To avoid danger zone, allow the cooked food to cool at room temperature and place it in the refrigerator within 2 hours. If you’re defrosting something, do it in the fridge or under cold running water.

#3 Set Your Refrigerator Temperature Below 4°C

Since the ‘Danger Zone’ for bacteria growth is defined as temperatures between 40°-140° F (4.4°-60°C), it is important that your refrigerator is set below 4°C to help mitigate the growth of bacteria.

Tip: Don’t put your meals in the compartments by the door as this is often the portion of the fridge where temperature fluctuates the most because it is exposed to outside air.

#4 Sensible Freezer Tips

Freezing does not kill bacteria, however it does stop bacteria from growing. Most food can last indefinitely in the freezer, but the tenderness, flavour and color of food can be affected.

Make sure you set your freezer temperature below 0°C. Proper wrapping is the key to successful freezer storage or freezer-grade plastic wrap or bags.

Don't be spooked by freezer burn, which occurs when food is not properly wrapped. As the FDA says, freezer burn is a “food quality issue, not a food safety issue.” Thaw frozen food in the refrigerator and then use it within two days.


#5 Education Yourself With Credible Information & Tools

It's also important to make sure you're doing all you can to support your digestive function. Our gut health affects the health of the rest of our body and it's important to ensure you're supporting your digestion with superfoods that aide digestion & elimination, help serve as an antioxidant & work on high quality absorption - this will help your body easily release all that is no longer required, all that can call harmful illnesses if left for too long in our system. A natural way to do this is through regular consumption of Pegaga by PurelyB. In addition to Pegaga by PurelyB, you'll want to audit the kind of ingredients you're consuming & the dishes you're eating. Are they working to serve your health or simply to satisfy your taste buds? In our Holistic Care Packageyou'll have a canister of Pegaga by PurelyB plus two virtual programs to guided you towards this. Created by Certified Nutritionist Amanda Teh and Nutrition Coach Carina Lipold, you'll learn the power of combining ingredients to make remedies that can cure ailments (constipation, flu, diarrhoea etc.) and learn how to make the yummy & healthy version of your favourite dishes - Asian & more! With such tools, you can feel rest assured you're doing all you can to support your gut, your immunity and therefore protecting your overall health against serious illnesses like cancer. 



#6 Generally, Cooked Food Will Only Last About 3-5 Days In The Fridge

If you want to prepare your food in advance, it’s best to do it twice a week and eat each meal within 3 days for the best condition. Generally food won’t last more than 5 days unless stored in the freezer. You can’t tell just by looking, smelling or tasting whether harmful bacteria has started growing in your foods.

So the general rule of thumb is to use up your food within 3-4 days if it is refrigerated, and frozen food within 4 months.

Common Recommended Refrigerator Storage Times:

(4°C or below)
(0°C or below)
Salads Egg, chicken, ham, tuna & macaroni salads 3 to 5 days Does not freeze well
Fresh Beef, Veal, Lamb & Pork Steaks 3 to 5 days 6 to 12 months
Chops 3 to 5 days 4 to 6 months
Roasts 3 to 5 days 4 to 12 months
Fresh Poultry Chicken or turkey, whole 1 to 2 days 1 year
Chicken or turkey, pieces 1 to 2 days 9 months
Soups & Stews Vegetable or meat added 3 to 4 days 2 to 3 months
Egg Hard cooked 1 week Do not freeze
Cooked Cooked meat or poultry 3 to 4 days 2 to 6 months
Chicken nuggets or patties 3 to 4 days 1 to 3 months
Pizza 3 to 4 days 1 to 2 months

Remember that these are only guidelines. When in doubt, throw it out!

#7 Can Nitrate Content In Overnight Vegetables Cause Cancer?

All green vegetable, and especially celery, carrots, beets, spinach and turnips have high amounts of naturally-occurring nitrates within them. When we eat these veggies raw, the bacteria in our mouth convert these nitrates into nitrites, which is naturally anti-inflammatory and can calm blood vessels and help increase blood flow.

The heating process converts nitrates in veggies into nitrites before they enter your mouth; each time you reheat them, the nitrites content increase, and nitrites (also a common preservative in processed meat product) is associated with cancer. However, there is still a considerable gap between the nitrate content in vegetables and the content of a harmful dose. There is no direct correlation between cancer and “reheating vegetables”.

From the food science perspective, the issue is not on the “overnight” fact, but on the preservative and storing condition. It isn’t recommended to reheat vegetables over and over again.

#8 Good Quality Storage Containers Will Help Keep Food Fresh Longer

Store and reheat your food using BPA-free plastic container or even better, with a glass container as heating and storing acidic food in plastic container may cause the release of carcinogenic chemicals from the plastic to the food.

All leftovers should be stored in sealable, shallow containers. While a bit more expensive, glass storage containers are the best choice as they will last longer, have a tighter seal, and you don’t have to worry about BPAs.

Exposure to BPA is a concern because of possible health effects on the brain, behaviour and prostate gland of fetuses, infants and children. Additional research suggests a possible link between BPA and increased blood pressure.

#9 Reheat Thoroughly Before You Eat

When reheating, make sure the temperature reaches 165°F (73.8°C). For sauces, soups and gravies, reheat them by bringing them to a rolling boil. Always cover your food during reheating, as it will retain the moisture and ensure the food is heat all the way through.

If you are in a hurry – it’s safe to reheat frozen food without thawing, but it will take longer time to cook. Never use saran wrap, plastic ware, or styrofoam to reheat food. If you must use the microwave, NEVER use containers or lids that are made of plastic in any form. Plastic cookware and coverings release a variety of harmful substances when heated.

You can reheat the small portions each time but return any unused portion to the refrigerator within two hours. Because the quality decreases each time food is reheated, it is best to reheat just the amount needed.


  1. Pablo M, Anju A, Adam D, Time Spent on Home Food Preparation and Indicators of Heathy Eating, American Journal of Preventive Medicine, Dec 2014 Vol 47, Issue 6, Pages 796-802,
  2. Pauline D, Caroline M, Vani A, Gladys I, Benjamin A, Emmanuelle KG, Serge H, Sandrine P, Meal planning is associated with food variety, diet quality and body weight status in a large sample of Frence adulst, International Journal of Behavioral Nutrition and Physical Activity, 2017, 14:12,
  3. Tina Haners, USDA Meat and Poultry Hotline. The Good, The Bad, The reheated: Cooking and Handling leftover,