Which of the following is a symptom of foodborne illness?

Nausea and vomiting are classic symptoms of foodborne illness. When individuals consume contaminated food, their bodies can react in various ways to rid themselves of the harmful pathogens or toxins. Nausea is often experienced as the body's way of signaling that something is wrong, prompting the need to expel the contents of the stomach. Vomiting can occur as a direct response to the stomach's irritation caused by these harmful substances. Recognizing these symptoms is crucial in identifying and mitigating the impacts of foodborne illness, leading to timely medical care if necessary.

In contrast, the other options do not align with the typical responses to foodborne illness. A normal appetite would generally indicate that no disturbance is occurring, while sudden weight gain and increased energy levels are not usually connected with the symptoms of foodborne illness, which typically involve a loss of appetite and overall reduced energy due to illness. Thus, understanding these symptoms is vital for effective food safety management and for preventing the spread of contamination.