Body Composition refers to the body’s relative amounts of fat, and lean body tissue or fat-free mass (eg, muscle, bone, water). Body weight can be subdivided simply into two components: fat weight (the weight of fat tissue) and fat-free weight (the weight of the remaining lean tissue). Percent body fat, the percentage of total weight represented by fat weight, is the preferred index used to evaluate a person’s body composition. Obesity is defined as an excessive accumulation of fat weight. Men have optimal body fat levels when the percent of body fat is 15% or less; they are considered obese when the body fat percentage is 25% and higher. The optimal body fat level for women is 23% or less, and they are considered obese when their body fat percentage is 33% or higher.
It is well established that excess body fat is associated with hypertension, type 2 diabetes, stroke, coronary heart disease, and hyperlipidemia.
Measurements of height, weight, circumferences, and skinfolds are used to estimate body composition. Although skinfold measurements are more difficult than other anthropometric procedures, they provide a better estimate of body fatness than those based only on height, weight, and circumferences.
Body Mass Index (BMI)
The BMI, or Quetelet index, is used to assess weight relative to height and is calculated by dividing body weight in kilograms by height in meters squared. For most people, obesity-related health problems increase beyond a BMI of 25, and the Expert Panel on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults lists a BMI of 25.0 to 29.9 kg m for overweight and a BMI of greater than or equal to 30.0 kg m for obesity. Although BMI fails to distinguish between body fat, muscle mass, or bone; an increased risk of hypertension, total cholesterol/ HDL cholesterol ratio, coronary disease, and mortality rate are associated with a BMI greater than 30 kg m. A BMI of less than 18.5 kg m also increases the risk of cardiovascular disease.
The pattern of body fat distribution is recognized as an important predictor of the health risks of obesity. Android obesity which is characterized by more fat on the trunk (abdominal fat), provides an increased risk of hypertension, type 2 diabetes, dyslipidemia, coronary artery disease, and premature death compared with individuals who demonstrate gynoid obesity (fat distributed in the hip and thigh).
The waist-to-hip ratio (WHR) is the circumference of the waist divided by the circumference of the hips and has been used as a simple method for determining body fat distribution. Health risk increases with WHR, and standards for risk vary with age and sex. For example, health risk is very high for young men when WHR is more than 0.95 and for young women when WHR is more than 0.86. For people 60 to 69 years old, the WHR values are greater than 1.03 for men and greater than 0.90 for women for the same risk classification.
The waist circumference can be used alone as an indicator of health risk because abdominal obesity is the issue. The Expert Panel on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults provided a classification of disease risk based on both BMI and waist circumference. Furthermore, a new risk stratification scheme for adults based on waist circumference has been proposed. This can be used alone or in conjunction with BMI to evaluate chronic disease risk. All assessments should include a minimum of either waist circumference or BMI, but preferably both, for risk stratification.