Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2001
Publication Date: April 1, 2001
Citation: Yokoi, K., Lukaski, H.C., Uthus, E.O., Nielsen, F.H. 2001. Use of bioimpedance spectroscopy to estimate body water distribution in rats fed high dietary sulfur amino acids. Journal of Nutrition. 131:1302-1308. Interpretive Summary: A relatively easy and noninvasive method to assess body composition and the effects of dietary factors on body composition is bio-electrical resistance. This method basically estimates total body water and its distribution - water found within cells (intracellular water) and water found outside of cells (extracellular water). Body composition can be estimated based on the amount of intracellular and extracellular water determined by this technique. The effect of dietary sulfur amino acids on electrical resistance and hence body composition was studied in rats. Weanling rats were assigned to groups of 12 and fed diets supplemented with either no additional sulfur amino acid or methionine or homocystine. After 9 weeks of feeding, urine was collected for measurements of creatinine, and then resistance was measured. Creatinine was measured to assess skeletal muscle mass. Rats fed methionine had significantly lower total body water, intracellular water and extracellular water compared to animals fed no supplemental sulfur amino acid. Rats fed homocystine had significantly lower extracellular water and had a significantly higher ratio of intracellular to extracellular water. These results suggest that dietary sulfur amino acids can alter the distribution of body water possibly by altering the porosity or thickness of cell membranes and that methionine and homocystine act differently in affecting the distribution of body water in rats. This study shows that the measurement of electrical resistance is a useful tool in determining body composition.
Technical Abstract: The effect of dietary sulfur amino acids on bioelectric properties was studied in rats by using bioimpedance spectroscopy. Weanling rats were assigned to groups of 12 in a factorially arranged experiment with dietary variables of supplemental sulfur amino acid (none, 10 g/kg dl-methionine or 10 g/kg dl-homocystine), pyridoxine hydrochloride (0 or 7.5 mg/kg) and nickel (0 or 1 mg/kg). After 9 weeks feeding, 20 h-urine was collected with fasting for measurements of creatinine, and then bioimpedance was measured by multifrequency (Hydra ECF/ICF 4200) and single frequency (RJL Systems Model 101) analyzers. Urinary creatinine excretion was explained by intracellular water (ICW), total body solid and urinary volume (R2 = 0.675). Extracellular water (ECW) did not add significantly to the model. Rats fed methionine had significantly lower total body water, ICW and ECW, than animals fed no supplemental sulfur amino acid. Rats fed homocystine had significantly lower ECW and had a significantly higher ratio of ICW to ECW. Animals fed methionine or homocystine had significantly lower capacitance corrected for body length and ICW, than those fed no supplemental sulfur amino acid. These results suggest that dietary homocystine changes distribution of body water and that sulfur amino acids increase membrane porosity and/or decrease membrane thickness.