Final answer:
Being underweight can lead to increased risk of infections, decreased muscle mass, and impaired immune function, which are all health concerns associated with undernutrition.
Step-by-step explanation:
The health problems associated with being underweight include a variety of concerns, notably an increased risk of infections, decreased muscle mass, and impaired immune function. This encompasses all the options provided in the question (4) All of the above.
Undernutrition, especially in children, can lead to wasting and stunting, conditions that reflect severe weight loss and inhibited growth due to insufficient nutrient intake.
Undernourished children are also more vulnerable to infections due to the weakened state of their immune system, which requires adequate nutrition to function properly.