(i) The criterion to determine if adults are undernourished is Body Mass Index, popularly known as BMI. (ii) In order to calculate it, first the weight of the person in kg is taken. Then, we take height in meters. The weight is divided by the square of the height. (iii) If this figure is less than 18.5, then the person would be considered undernourished. However, if this BMI is more than 25, then a person is overweight.