Academic Presentation

Near IR-Light Single Site Body Fat Testing  

Robert D. Rosenthal – Oslo Norway January 1991 

In an attempt to understand why the single body site (i.e. the biceps) provides identical accuracy as multiple sites, a test on hogs was performed. This test Involved approximately 400 hogs each of which were measured at 11 different body sites. (1)  

After the normalized second derivative near-IR measurements were made, the hogs were sacrificed and then ground using a typical supermarket meat grinder. The ground meat was then well mixed (I.e. blended) and then fine ground until it became a pureed sample. The entire pureed sample was then statistically sub-sampled. The sub-samples were combined, then well mixed. The resultant sample was considered representative of the entire hog. 

The fat in this sample was analyzed using the solvent (ether) extract method. This official chemical method was proved to have accuracy on these types of samples of 0.2%. This method of measurement of meat is similar to the method used in over 3,000 supermarkets in the United States. In those supermarkets, near-infrared instruments are used to measure ground beef with a demonstrated accuracy of 0.2% when compared to either extract test.  

It was further shown that if the best seven sites were used, the accuracy remained 0.2%. However, if the number of sites was reduced to five, the accuracy diminished to 0.5%. Likewise, for the best three sites, the accuracy became 1% and for the best single site the accuracy was 2.8%. It is believed that this is a significant finding i.e. that the measurement of hogs at a single body site provided essentially the identical accuracy as single-site measurement provides on people. 

To partially substantiate these results, a small study was then made whereby five hogs were measured using underwater weighing techniques. (2)  The test procedure used a special sling that allows weighing the animals out of the water and weighing them underwater. An oxygen mask was provided allowing the hogs to breathe while they were underwater. To do this test, the pigs were tranquilized and an artificial method was used that caused the pigs to exhale most of the air in their lungs during underwater weighing. At the completion of the hydrostatic tests, the hogs were sacrificed and their body fat determined via the ether extract method. 

Although it is recognized that this limited underwater weighing test was not optimum, It did provide the Interesting result that the underwater accuracy was 2.9%  This Is essentially Identical to the 2.8% accuracy obtained by near-Infrared on a single site on people. It Is believed that these tests on hogs provide credence that the reason that a single site on humans provides the same accuracy as multiple sites is due to the Inherent errors in the official method of performing body fat measurement; I.e. the Inherent errors in underwater weighing techniques.  Saying this differently, If It was permissible to calibrate a near-infrared Instrument by grinding the subjects up to and performing an ether extract test, then multiple sites probably would provide better accuracy than the single site. However, since the accuracy of the official underwater weighing method is limited to approximately three percent, no additional accuracy can be obtained using near-IR measurements at multiple sites. 

Bibliography:  

1. Research on Non-Invasive Measurement of Body Fat in Live Hogs; Trebor

Industries Inc. Internal Research Report, Number 1989-16. 

2. A Method for Hydrostatically Weighing Live Hogs; Trebor Industries Inc. Internal

Research Report; Number 1989-3. 

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