Which of the following can be a symptom of a foodborne illness?

Nausea, vomiting, diarrhea, and fever are common symptoms associated with foodborne illnesses. These symptoms occur due to the body's response to harmful pathogens or toxins present in contaminated food or beverages. When the body detects these threats, it activates the gastrointestinal system to expel the harmful substances, leading to nausea and vomiting. Diarrhea is another way the body attempts to rid itself of these pathogens or toxins through increased fluid secretion and rapid movement of contents through the intestines. Fever often occurs as part of the immune response, signaling that the body is fighting off an infection.

The other options may not be directly related to foodborne illnesses. Headache and body aches can sometimes accompany illnesses, but they are more general and not specific to foodborne pathogens. Weight gain is not relevant as a symptom of foodborne illness; rather, it is often a result of excess caloric intake over time. Loss of appetite might occur, but it is more of a general symptom of various health issues and does not typically characterize foodborne illnesses specifically like the combination of nausea, vomiting, diarrhea, and fever does.