Table 2

 Illustration of the advantages and disadvantages of different techniques for measuring body composition in clinical practice. The patient is a 14 year old girl referred for assessment and management of obesity with associated type 2 diabetes. Which measurements might be useful in terms of baseline assessment and monitoring of body composition during weight loss?

BIA, bioelectric impedance analysis; BMI, body mass index; DXA, dual energy x ray absorptiometry; FFM, fat-free mass; FM, fat mass.
Conclusions: In practical terms, the techniques most useful in this patient are BMI and waist circumference for monitoring nutritional status and central fat distribution. If available, DXA could be used for assessing changes in limb lean mass, and densitometry or deuterium could also provide longitudinal data for both fat and lean mass.
Simple measurements
Skinfold thicknessPoor accuracy and precision in obesity
BMIUseful as a simple baseline and longitudinal measurement of relative weightWill not allow assessment of fat and lean masses and changes in fat which may be more relevant in terms of metabolic risk
Waist circumferenceUseful baseline and longitudinal measurement. Centile charts are available, and central fatness is of greater relevance to metabolic risk
Predictive measurements
Skinfold thickness equations predicting FM and FFMPoor precision and accuracy—any error will be magnified by the use of prediction equations not derived from a comparable (obese) population
Whole body BIACould provide information on the direction of longitudinal changes in lean massPoor accuracy in absolute terms. Changes in body weight, the relative proportions of trunk and limbs, or FFM hydration with treatment could introduce further errors
Two-component techniques
DXACould be used to measure regional (limb) lean mass which could provide information on whether weight loss is accompanied by changes in lean mass as well as fat massLimited use for measuring baseline fat mass or longitudinal changes in fat mass with weight loss, since measurements are known to be biased by body size (thickness)
Densitometry (BodPod)Could provide longitudinal data on both lean and fat mass since its accuracy is less likely to be affected by changes in fatness.Does not provide regional data.
Deuterium dilutionCould estimate whole body lean massResults may be affected by the small differences in FFM hydration in obesity, but these have been quantified and could be adjusted for. Small differences in FFM hydration would introduce minor errors in the short term