Which of the following is a common symptom of foodborne illness?

Nausea and vomiting are indeed common symptoms of foodborne illness. These symptoms often occur as the body’s response to harmful pathogens or toxins that have been ingested. The gastrointestinal tract tries to expel the contaminating substances to protect the body from further harm, which is why nausea and vomiting frequently accompany foodborne illnesses.

In contrast, the other options listed do not align with the typical effects experienced during foodborne illness. Increased energy and alertness, weight gain, and improved focus are generally not associated with reactions to contaminated food. Instead, foodborne illness can lead to fatigue, dehydration, and other distressing symptoms that make it difficult for individuals to maintain their usual energy levels and mental clarity.