Final answer:
The main limitation of using BMI to determine obesity and disease risk is its inability to differentiate between muscle and fat mass and to account for the distribution of body fat, which are important factors in evaluating health risks.
Step-by-step explanation:
The limiting factor when using the Body Mass Index (BMI) to determine obesity and disease risk is that BMI does not account for fat mass or fat distribution. It is a simple measure based on weight and height and can therefore sometimes underestimate the amount of body fat in overweight individuals and overestimate it in those with more muscle mass. Differences in body composition, like the proportion of muscle to fat, and where the fat is distributed (visceral versus subcutaneous), are significant predictors of health risks but are not reflected in BMI calculations. Populations such as athletes who typically have greater muscle mass may be misrepresented by this index. Additionally, BMI-associated health risks can vary by race and age, further complicating its accuracy as a universal tool for diagnosing obesity or assessing disease risk.