Energy metabolism and thyroid hormone levels of growing rats in response to different dietary proteins ‐ soy protein or casein

Abstract

Energy balances were measured by indirect calorimetry in four experiments on male growing rats, fed restrictively on isoenergetic and isonitrogenous (10% CP) diets based on either casein supplemented with methionine, or soy protein isolate (experiments 1, 2 and 3) and soy protein isolate supplemented with methionine (experiment 0), respectively. At the end of experiments the rats were killed for body analysis and determination of thyroid hormones and lipids in blood as well as mitochondrial respiration in liver and heart. Feeding of non-supplemented soy protein resulted in a lower efficiency of energy utilisation as well as a lower protein utilisation compared to casein-fed and supplemented soy protein-fed rats. Chemical body composition was not markedly different between the dietary groups. After long-term feeding of soy protein (experiment 3) mass and mitochondrial protein content of the interscapular brown adipose tissue were increased compared to casein-fed rats. Serum thyroid hormone levels were not changed (T3 and free T3) or were significantly lowered (T4 and free T4) following soy protein feeding in comparison with casein feeding (except for experiment 2). Cholesterol and triglycerides were decreased on an average in response to soy protein or supplemented soy protein feeding. In two of three experiments a significant lower efficiency of hepatic mitochondrial respiration with succinate as substrate, expressed by the ratio of added ADP to oxygen consumed, was observed in soy protein-fed rats compared to casein-fed rats.

Effect of Different Levels of Supplemental Yeast on Body Weight, Thyroid Hormone Metabolism and Lipid Profile of Broiler Chickens

“…This finding further confirms the role of the yeast Saccharomyces cerevisiae as an excellent system in which to study thyroid hormone receptor action [32]. Klein et al [25] reported that soy protein isolate had no effect on T 3 and free T 3 , but significantly decreased T 4 compared with casein in rats. The decrease in T 4 concentration may be responsible for the cholesterol-lowering effect of Saccharomyces cerevisiae, since T 3 is responsible for the maintenance of cholesterol homeostasis in the vascular endothelial lining [40,59].…”

Effects of dietary protein quality on energy metabolism and thyroid hormone Status in growing pigs

“…In addition the higher excess of ME in SPI-, in comparison to CAS+, seems to be divided into both FER and HP. Analogous experiments with growing rats fed low protein diets based on SPI-or CAS+ (KLEIN et al, 2000) are not consistent with our findings of a similar energetic efficiency in SPI-and CAS+ fed pigs. The SPI-fed rats retained both less protein energy and fat energy in comparison to CAS-fed rats.…”

Expression of genes participating in regulation of fatty acid and glucose utilization and energy metabolism in developing rat hearts

“…1. development seemed to be closely related to changes in insulin, thyroid hormone (33), and glucose concentrations in blood (17,59). Another important point of these changes is that glucose uptake becomes insulin sensitive after 2 wk of life (23,28).…”

“…Thyroid hormone has received wide attention as a possible trigger of developmental changes in infant rats, because its circulating concentration increases significantly during the second postnatal week (33,61,68).…”