Final answer:
An underweight BMI is below 18.5 kg/m², and a healthy BMI is between 18.5 and 24.9 kg/m². Underweight individuals may be at risk for malnutrition and weakened immune system, while individuals with a healthy BMI have a lower risk of chronic diseases.
Step-by-step explanation:
The Body Mass Index (BMI) is used to measure body weight relative to height. An underweight BMI is typically less than 18.5 kg/m² while a healthy BMI falls between 18.5 and 24.9 kg/m².
Regarding disease risks, individuals with an underweight BMI may be at risk for malnutrition, weakened immune system, osteoporosis, and anemia. On the other hand, individuals with a healthy BMI have a lower risk of developing chronic diseases like cardiovascular disease, type 2 diabetes, and certain types of cancer.