Table 1

Summary of assumptions underlying different techniques, their availability, and their main advantages and disadvantages

Technique	Assumptions made	Reference data	Availability*	Advantages/disadvantages
*Availability: +, low; ++, medium; +++, high.
†Densitometry by air displacement plethysmography (Bodpod)
AT, adipose tissue; D_f, density of fat; D_ffm, density of fat-free mass; D_min, density of mineral; D_prot, density of protein; F, fat; FFM, fat-free mass; H_ffm, hydration of fat-free mass; K, potassium; Var, variability.
Skinfolds – raw	Constant skin protein content	Y	+++	For: simple measure of regional fat
				Against: no information on lean mass

Skinfolds – equations	Skinfolds ∝ whole body fat	N	+++	For: simple and quick
Skinfolds – equations	Skinfolds ∝ whole body fat			Against: population specific, poor accuracy in individuals and groups

Body mass index	Var weight = var fat	Y	+++	For: simple and quick
				Against: measures nutritional status not body composition

Waist circumference	Waist ∝ central fat	Y	+++	For: simple, quick, robust measure of abdominal fat
				Against: not so accurate as measure of internal visceral fat

Impedance	Conductivity ∝ body water	N	++	For: simple and quick
	Conductivity ∝ body water			Against: population specific; poor accuracy in individuals and groups

DXA	Constant attenuations of FFM and F	N	++	For: accurate for limb lean and fat
	Constant attenuations of FFM and F			Against: radiation exposure; whole body bias ∝?size, sex, fatness

Densitometry†	Constant D_ffm and D_f	N	+	For: acceptable two-component technique
				Against: effects of disease on lean mass reduce accuracy

Isotope dilution	Constant H_ffm	N	+	For: only technique acceptable in all age groups
				Against: delayed results; inaccurate if disease affects H_ffm

MRI	Electromagnetic properties	N	+	For: accurate for regional AT
	Electromagnetic properties			Against: expensive, limited availability, measures AT not fat

TOBEC	Conductivity ∝ body water	N	+	For: acceptable two-component technique
	Conductivity ∝ body water			Against: rarely available, accuracy unknown

TBK	Constant K in cell mass	N	+	For: measures functional component of body composition
				Against: rarely available, poor accuracy for fatness

Multicomponent models	Constant D_prot and D_min,	N	+	For: most accurate approach, all measurements acceptable
	constant mineral composition			Against: expensive, specialist research approach