The significance of body mass index (BMI) in assessing health lies in its ability to evaluate body weight relative to height, serving as a simple screening tool for potential weight-related health issues. While it does not directly measure body fat, BMI helps categorize individuals into weight categories (underweight, normal, overweight, obese). This categorization aids healthcare professionals in identifying those at risk for conditions like diabetes, heart disease, and certain cancers, guiding interventions for improved health.