Ideal Body Weight Is Not Really Ideal

As Moreault et al.¹  recently discussed in this journal, some anesthetic management guidelines as well as many drug dosing regimens²  are based on a patient’s ideal body weight (IBW). Despite being an important measure in clinical practice, there is no consensus as to what IBW really represents or how to calculate it.³  IBW has no physiologic basis and there is no single weight that is ideal for any patient of a given height.⁴  For both men and women, IBW often is described as a body mass index (BMI; BMI = kg/m²) between 20 and 25 kg/m². BMI is not a measure of adiposity because it considers weight irrespective of the source, and excess amounts of fluid, muscle, and bone can each increase BMI.

Given that adipose is poorly perfused and contributes minimally to metabolism, fat-free mass or lean body weight (LBW) would be a better measure for clinical purposes. LBW can be obtained using dual-energy x-ray absorptiometry, but measurements are cumbersome and difficult to apply in clinical medicine.⁵  The many formulae currently used to estimate IBW give widely different values for the same patient. In the absence of a simple equation for LBW, we agree with Moreault et al. that height (M²) x 22 is a simple formula that can be used clinically to estimate ideal weight.^1,4 

Support was provided solely from institutional and/or departmental sources.

The authors declare no competing interests.