If the body’s weight is between 10% – 20% less or more as compare to Ideal body weight, it will be considered as underweight. If body weight is below 20% or more than 20%, person would be considered as grossly underweight. Underweight is a common problem and mostly affected with poverty, poor living conditions and long term diseases, physiological difficulty in weight gain and maintenance. For measuring underweight condition, BMI is an effective tool to measure. If BMI is less than 18.5, the condition would be underweight.