Near infrared interactance

  1. The near infrared interactance (NIR) method of assessing body composition is based on the principles of light absorption reflectance, and near infrared spectroscopy.
  2. More specifically it is based on the ability of fat tissues to "absorb" more infrared light than lean tissue which can then be measured as a change in the infrared level.
  3. The use of infrared (IR) light to measure fat was developed by the US Department of Agriculture to measure the fat contained in beef and pork carcasses after slaughter.
  4. At approximately 928 nanometers, a direct measure of how much fat exists is provided by the absorption of the infrared portion of the spectrum.

A mono-chromator or light "wand" (see Figure 1), sends a low-energy beam of near-infrared light at about 900 nanometers into the biceps area that penetrates the underlying tissue to a depth of one centimetre. The energy is either reflected, absorbed, or transmitted, depending on the scattering and absorption properties of the biceps. A detector within the wand measures the intensity of the re-emitted light. Shifts in the wavelength of the reflected beam and a prediction equation are used to compute the percent body fat.

This measure is rarely used for the assessment of body composition. Although it has good repeatability, it lacks validity in humans and its inability to accurately predict body fat across a broad range of fat levels is problematic. It assumes fat in the arm is proportional to total body fat, and research suggests that NIR may overestimate body fatness in lean people and underestimate it in people who are overweight.

The NIR data (density measurements) are entered into a prediction equation with the person's height, weight, age, gender, frame size, and level of physical activity. A digital read out including percentage body fat and lean tissue are displayed.

Figure 1 Example of Near Infrared Interactance.
Source: wikiHow.

An overview of the characteristics of near infrared interactance is outlined in Table 1.


  1. NIR measurement is safe and the equipment is portable and lightweight.
  2. It requires little training to use.
  3. The tool has a high level of repeatability.


  1. The amount of pressure applied to the fiber optic probe, skin color and hydration levels may cause results to differ and be inaccurate.
  2. Some instruments have been shown to underestimated body fat by more than 4% in subjects greater than 30% fat and overestimated body fat by 4% in subjects less than 8% fat.
  3. Poor validity.

Table 1 Characteristic of near infrared interactance.

Characteristic Comment
Number of participants Small
Relative cost Low
Participant burden Low
Researcher burden of data collection Low
Researcher burden of coding and data analysis Low
Risk of reactivity bias No
Risk of recall bias No
Risk of social desirability bias No
Risk of observer bias Yes
Space required Low
Availability High
Suitability for field use High
Participant literacy required No
Cognitively demanding No

Considerations relating to the use of NIR are summarised by population in Table 2.

There are no specific population for whom NIR cannot be implemented. It is easily administered and has shown a high level of repeatability. However, there is no research to support this method of body composition assessment in some populations and in the remainder, evidence highlights its poor accuracy and validity levels when compared to other more well established techniques such as hydrostatic weighing.

Table 2 Anthropometry by near infrared interactance in different populations.

Population Comment
Pregnancy No research to support
Infancy and lactation No research to support
Toddlers and young children Not suitable *
Adolescents Not suitable *
Adults Not suitable *
Older Adults Not suitable *
Ethnic groups Not suitable *
Other (obesity) Not suitable *

*Based on poor validity.

The only known possible restriction on NIR is to avoid measurements on an extremely black tattooed location. The low energy NIR light might be totally absorbed by a very black tattoo.

Refer to section: practical considerations for objective anthropometry

  1. NIR (Futrex) Body Composition Analyser
  2. NIR (SCiO consumer physics) scanners with supporting devise requiring application with web interface

A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.

The NIR (SCiO consumer physics) scanner is a new device. However, no validation work has been carried out to date to assess its use in the assessment of body composition.

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