Evaluation of near infra-red interactance for assessment of subcutaneous and total body fat

Abstract

Objective: Near infra-red interactance (NIRI) has been used for assessment of total body fatness, but its relationship with composition at the measurement site is not clear. This study examines the relationship of interactance with subcutaneous adipose tissue and muscle thickness as well as total body fat content.

Design: (i) Validation of NIRI by comparison with subcutaneous tissue thicknesses from ultrasound. (ii) Cross-validation of techniques for estimation of body fat content.

Setting: Laboratory.

Subjects: (i) 54 young adults (27 male and 27 female) and (ii) 63 middle-aged men.

Interventions: Measurements of subcutaneous adipose tissue thickness and muscle thickness using ultrasound, near infra-red interactance (Futrex 5000) and skinfold thicknesses were made at five sites in young adults. In middle-aged men total body fat was assessed by densitometry, NIRI and skinfold thickness. Measurements were made in duplicate by a single trained observer.

Results: Interactance measurements were related to subcutaneous adipose tissue thickness, although the relationship varied according to measurement site r = 0.09 at anterior thigh to 0.78 at biceps; P = 0.31 to < 0.0001). Muscle thickness explained additional variance in interactance only at biceps in women. Subcutaneous adipose tissue thickness correlated better with skinfold thickness (r = 0.56 to 0.92; P = 0.002 to < 0.0001) than with interactance. Mean difference in fat mass from densitometry +/- 95% limits of agreement was -1.61 +/- 7.68 kg for NIRI and -2.84 +/- 6.56 kg for skinfold thickness in middle-aged men. NIRI tended to underestimate higher (and overestimate lower) levels of fatness.

Conclusions: NIRI performed no better than skinfolds in assessment of either subcutaneous or total body fat.