Everyone tries to choose nutrient-rich foods for their family meals. Some even cook in advance so they can conveniently bring food to work the next day—ensuring nutrition and hygiene. However, there are certain dishes you need to be cautious about if you don’t want to unknowingly bring health risks upon yourself.

Today, while technology continues to advance, our quality of life in some aspects is declining. Prioritizing work too much often leads to stress and imbalance. On top of that, the fast-paced lifestyle means many people frequently eat out to save time.

That’s why more and more people are looking for solutions to this eating problem. One of the most practical and cost-effective ways—while ensuring quality—is to bring a homemade lunchbox. At the office, all you need to do is heat it in the microwave and enjoy, without having to step outside in the heat or wait for delivery.

However, an important point to remember is that some foods can deteriorate when kept overnight. Eating them may lead to food poisoning, digestive disorders, or even long-term chronic illnesses. Below are 5 foods that should never be left overnight.

1. Seafood

Seafood is rich in essential vitamins and minerals, especially calcium for bone health and zinc, which is beneficial for acne-prone skin.

However, reheating seafood multiple times can cause it to lose nutrients and become harmful. When left overnight and reheated, the proteins in seafood undergo changes that can damage the liver and kidneys.

Instead, if you want to eat seafood, consider steaming it fresh in the morning—it doesn’t take much time, and you can prepare other personal tasks while waiting. This way, you retain the nutrients and flavor.

2. Eggs

Eggs are a favorite food for many, thanks to their quick preparation, rich nutrition, and versatility in countless dishes.

While boiled eggs can be refrigerated overnight and eaten the next day without much issue, fried eggs or sunny-side-up eggs don’t keep well—they lose flavor and may harbor bacteria if undercooked or left runny.

Since eggs cook very quickly, it’s best to prepare them fresh in the morning for both taste and safety.

3. Chicken

This might come as a surprise, as many people think cooked chicken can last in the fridge for several days. While that’s true, reheating chicken may cause protein structures to change, making it harder to digest and potentially causing stomach discomfort, especially for those with weak digestion.

Chicken is a great source of lean protein, helps build muscle, reduces the risk of colon cancer, and even contains compounds that relieve stress and mild depression. However, to maximize these benefits, chicken should be prepared and stored properly rather than reheated repeatedly.

4. Vegetable Soups and Broths

For Vietnamese families, meals usually include at least one savory dish and one soup—often made with vegetables or root crops for added vitamins and fiber.

However, experts from the National Institute of Clinical Nutrition warn against keeping vegetable soups overnight. Green vegetables contain nitrates, and when cooked and left for too long, especially with bacterial activity, nitrates can turn into nitrites. Once inside the stomach, nitrites can form N-nitroso compounds, which are highly carcinogenic—linked to cancers of the esophagus, stomach, and other digestive organs.

5. Cooked Mushrooms

Mushrooms are a staple in daily meals, cooked in soups, stir-fries, stews, grills, or hot pots. Many households refrigerate leftover mushroom dishes to reheat the next day, not realizing this habit could be harmful.

Like vegetables, mushrooms contain nitrates. While nitrates themselves benefit red blood cells, storing mushrooms overnight and reheating them repeatedly converts nitrates into nitrites—known carcinogens that increase the risk of digestive system cancers, such as those in the stomach, colon, and esophagus.

In conclusion, while meal-prepping and bringing food from home is a great habit for saving money and maintaining nutrition, it’s important to remember that not all foods are safe to keep overnight. For your family’s health, avoid storing seafood, fried eggs, chicken, vegetable soups, and mushrooms for the next day. Instead, try to cook them fresh whenever possible.