the body mass index bmi is a simple index of weight for height that is commonly used to classify overweight and obesity in adults it is defined as a persons weight in kilograms divided by the square of hisher height in meters kgm however it should be considered only an indicative guideline because it may not correspond to the same degree of overweight and obesity in different individuals however the respective public health burdens of overweight and undernourishmentmicronutrient deficiencies are not quantified only in terms of the number of people affected