Evaluation of near infra-red interactance as a method for predicting body composition.

The ability of near infra-red interactance (NIRI) to predict body composition, as measured by whole-body densitometry, was assessed in a group of 29 healthy volunteers; 15 m, 14 f, aged 18-40 years, body mass index (BMI) 18.3-28.5 kg/m2. The results were compared with those obtained by five other predictive methods: whole-body impedance/resistance, skinfold thicknesses, and methods based on weight and height or BMI. The correlation between densitometry and the alternative methods, including NIRI, were found to be remarkably similar, both with respect to fat (r = 0.90-0.92, s.e.e. = 2.12-2.47 kg), and fat-free mass (r = 0.96-0.97, s.e.e. = 2.13-2.71 kg). Percentage body fat (densitometry) correlated better with the near infrared measurements made in the biceps area than with those made in the triceps or thigh areas, or with a combination of measurements made at two or three sites. The 95 per cent limits of agreement between NIRI and densitometry for the estimation of body constituents were slightly greater than those between densitometry and the other methods. NIRI was also found to underestimate body fat increasingly as the degree of adiposity increased. This under-estimation was found to be particularly marked (16 per cent body weight) in a small and separate group of grossly obese women, BMI greater than 50 kg/m2, whose body composition was assessed by total body potassium as well as by densitometry. This study suggests that, in the healthy group of subjects examined, NIRI has little or no advantage over other simple methods in predicting body composition measured by classical whole-body densitometry.