Weight is the heaviness of a person. In children, weight is routinely used as an index of growth. In healthy adults, weight remains more or less stable if dietary energy intake matches energy expenditure (metabolism). Weight loss or weight gain occurs if the net energy balance is disturbed.

WEIGHT ASSESSMENT

The standard method of assessing weight is to use the body mass index (BMI), obtained by dividing the weight in kilograms by the square of the height in metres. A BMI of less than 18.5 kg/m2 is classed as underweight; 18.5-24.9 kg/m2 is classed as a healthy weight; 25-29.9 kg/m2 is classed as overweight; 30-39.9 kg/m2 is classed as obese; and a BMI over 40 kg/m2 is classed as very obese. These figures are general ones that apply to most healthy adults under the age of 60. They are not applicable to children; people over 60; people with chronic health problems; women who are pregnant or breastfeeding; or people with a high proportion of muscles, such as athletes.

The proportion and distribution of body fat is also important: people with too much fat around the waist are at increased risk of health problems, even if their BMI is in the healthy range. For average men aged 20-60 with no chronic health problems, body fat should account for about 22-35 per cent of total body weight, and the waist should be no larger than 81cm.

In children, weight can be compared with standardized predictions for age, which differ according to the gender and race of a child. Such weight charts may be used to access how well a child is thriving. Special BMI charts for children are also available but they require expert interpretation because a child’s BMI may change rapidly, due to a growth spurt, for example.

WEIGHT AND HEALTH

At all ages, divergence from standard figures (either using BMI or body fat percentages) may have medical implications. If an individual is underweight, his or hers nutrition may be inadequate as a result of a poor diet or disease; if an individual is significantly overweight, he or che is at an increased risk of various health problems, such as hypertension (high blood pressure), coronary artery disease, stroke, and diabetes mellitus.

Source: A-Z family medical encyclopedia by BMA

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