Submitted to: Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/28/2001
Publication Date: 7/1/2001
Citation: Lukaski, H.C., Hall, C.B., Marchello, M.J. 2001. Validation of dual x-ray absorptiometry for body composition assessment of rats exposed to dietary stressors. Nutrition. 17(7-8):607-613. Interpretive Summary: Although the rat is used as a model to assess the effects of various dietary manipulations on nutritional status, there is a lack of an established method to determine fat and non-fat, non-bone components in the living animal. This deficit is more pronounced if experimental manipulations cause changes in water content of the animal. We evaluated the accuracy and precision of dual x-ray absorptiometry compared to chemical analyses to determine the body composition of rats fed various experimental diets designed to maintain normal body weight and composition as well as to cause obesity, acute and short term starvation, and alterations in body water. The dual x-ray absorptiometry determinations were very highly correlated with chemical measurements. Also, regardless if the animal was positioned on its back (supine) or its abdomen (prone), the x-ray determinations were very repeatable. However, the DXA method, regardless of position of the rat, significantly underestimated the non- fat component by 3% and overestimated the fat component of the body by 3- 25%. The large differences seen between chemical and x-ray determinations are explained partially by the altered water status of some groups of animals. This finding is consistent with the observations of other investigators and emphasizes the need to revise the equations used to calculate body fat based on the x-ray absorption and transmission in the body of small rodents. This information will be useful to researchers who seek to measure body soft tissue composition of laboratory rodents repeatedly without sacrificing the rat.
Technical Abstract: Evidence of the validity and accuracy of dual x-ray absorptiometry (DXA) to measure soft tissue composition of laboratory rats with altered body composition associated with nutritional perturbations is lacking. We compared DXA determinations made in prone and supine positions with measurements of chemical composition of 49 male, weanling Sprague-Dawley rats that were fed the basal AIN-93 growth diet (CN), the basal diet modified to contain 30% fat (FAT), fasted for 2 d (FST), limit-fed 6 g basal diet daily for 1 week (LMF), and treated with furosemide (10 mg/kg ip 2 hr before DXA; DH). DXA yielded similar estimates of body mass and soft tissue composition in the prone and supine positions. DXA estimates of body composition were significantly correlated with reference compositional values (R2 = 0.371- 0.999). DXA discriminated treatment effects on body mass (BM), fat-free, bone-free mass (FFBFM), fat mass (FM), and body fatness (%FAT); it significantly underestimated BM (1-2 %) and FFBFM (3 %) and significantly overestimated FM and %FAT (3-25 %). The greatest errors occurred in treatment groups in which BM was diminished and body hydration was decreased. These findings suggest that DXA is capable of determining small changes in FFBFM in response to obesity and weight loss. Errors in DXA determination of FM and %FM associated with extra corporeal fluid and dehydration indicate the need for revision of calculation algorithms for soft tissue determination.