Generally, it's not recommended to keep food warm for extended periods, as this accelerates spoilage, especially for foods rich in protein and water. For example, cooked porridge should not be kept warm for more than 6-8 hours; otherwise, bacteria may grow, and its nutritional value and taste will decline. For meat, fresh meat should not be refrigerated for more than two days, while cooked meat can be refrigerated for slightly longer, but is still best consumed within a week.
Furthermore, some specific foods, such as leafy green vegetables, may produce higher levels of nitrites during the warming process. Long-term consumption of such foods is detrimental to health.