Diet-Induced Thermogenesis and Expression Levels of Thyroid Hormone Target Genes and Their Products in Rats Differ between Meat Proteins.

We compared the effects of purified meat proteins on postprandial thermogenesis and on the secretion of and responsiveness to thyroid hormones (THs) in rats. Body temperatures at 2 h after feeding were significantly higher in the chicken and mutton protein groups than in the other groups, and these proteins seem to have a strong thermogenic effect. There were no significant differences in plasma TH concentrations among the groups, but levels of TH-responsive Spot 14 protein in the liver and brown adipose tissue were significantly higher in the chicken and mutton protein groups than in the other groups. Levels of malic enzyme 1 protein in the liver and brown adipose tissue were significantly higher in the chicken protein group than in the other groups except for the mutton protein group. Furthermore, levels of uncoupling protein 1 were higher in the chicken and mutton protein groups than in the other groups. The results suggest that the difference in postprandial thermogenesis of meat is strongly dependent on meat proteins; chicken and mutton proteins are strong promoters of postprandial thermogenesis, and THs may contribute to this effect. Since strong postprandial thermogenesis and high expression levels of TH target genes and their products were not observed in the amino acid group, chicken and mutton proteins or their digested peptides might contribute to these effects.