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1.18 ESTIMATION OF LEAN BODY WEIGHT

               Total body weight has two components, lean body weight and fat weight. Lean body weight includes the muscles, bones, tendons, ligaments and water in the body. Fat weight includes the fat stored in the fat cells and the organs of the body.

               The majority of human body composition measurements have used indirect techniques based on different assumptions about the chemical or physical properties of lean body weight. Lean body weight can be estimated as the difference between body weight and total adipose tissue expressed in kilograms. The conversion from litres of total adipose tissue is achieved by multiplying with the mean density (0.923) of human adipose tissue. The algorithm¹ below may be used to obtain estimates of lean body weight for use in calculating doses of drugs with narrow therapeutic index.

Males

Total AT = 1.36 × W/H – 42.0

Females

Total AT = 1.61 × W/H – 38.3

Males and Females

LBW = BW – (Total AT × 0.923)

in which AT is adipose tissue in litre, BW is body weight in kg, LBW is lean body weight in kg, W/H is weight/ height in kg/m.

¹ Modified from A.J. Stunkard, T.A. Wadden, Obesity: Theory and Therapy, 2^nd ed., New York, Raven Press, 1993, pp.14-19.