The heaviness of a person or object. In children, weight is routinely used as an index of growth. In healthy adults, weight remains more or less stable as dietary energy intake matches energy expenditure (see metabolism). Weight loss or weight gain occurs if the net balance is disturbed. Weight can be compared with standardized charts for height, age, and sex. At all ages, divergence from the normal weight for height may have medical implications. For example, if weight is below 80 per cent of the standard weight for height, the individual’s nutrition is probably inadequate as a result of poor diet or disease, and if 20 per cent above the standard, he or she is considered to be suffering from obesity. An alternative method of assessment is use of the body mass index (BMI, or Quetelet’s index), obtained by dividing weight in kilograms by the square of height in metres. A healthy weight is 20–25 BMI; a BMI of greater than 25 indicates that a person is overweight.


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