Can leftover food from the previous day be eaten if it was not refrigerated overnight?

Whether leftover food kept overnight without refrigeration is safe to eat the next day depends on the season.

“Leftover food” typically refers to vegetables, staple foods (e.g., rice or noodles), and meats. In summer, if such food is left unrefrigerated overnight, it often fosters rapid microbial growth. Individuals with sensitive digestive systems who consume it may experience gastrointestinal symptoms—including nausea, vomiting, bloating, abdominal pain, and diarrhea—and thus it is generally not recommended for consumption to avoid adverse health effects. Additionally, leftover dishes—especially vegetables—may contain elevated levels of nitrites. Regular consumption of such leftovers could lead to chronic exposure to this harmful substance, thereby increasing cancer risk.

In winter, ambient temperatures are low enough to inhibit bacterial growth and reproduction—even though cold weather alone does not kill bacteria. Provided the food remains free from contamination by pests (e.g., cockroaches or rodents), consuming it after one day’s storage at room temperature usually poses minimal health risks. However, if left for too long, food may still spoil—becoming slimy, sour, or otherwise deteriorated—and consumption could trigger gastrointestinal discomfort.