What symptom is most commonly associated with foodborne illness?

Nausea or vomiting is the symptom most commonly associated with foodborne illness because these reactions are the body's way of expelling harmful substances after consuming contaminated food or water. When pathogens, such as bacteria or viruses, are ingested, they can irritate the gastrointestinal tract and trigger these symptoms as a protective measure. This response is typically among the first indicators that something is wrong, often leading to additional symptoms such as diarrhea or abdominal pain. Other choices, like increased appetite, weight gain, or increased energy levels, do not align with the typical responses to foodborne illnesses, which generally result in discomfort and loss of appetite. Therefore, nausea or vomiting stands out as a clear warning sign of potential foodborne illness.