What is BMI and what does it measure?
BMI is a simple measure of weight in relation to height. It estimates percentage of body fat, and is used to broadly measure weight-related health risk.
A higher percentage of body fat is proven to be associated with increased risk for developing certain diseases such as heart disease, high blood pressure, type 2 diabetes, breathing problems, certain cancers and a higher risk of early death.
Underweight is the range of weight that is lower than what is generally considered healthy for a given height. It may indicate underlying medical conditions or an eating disorder, plus higher risk for conditions such as osteoporosis.