SummaryWe investigated the postprandial thermic effect of chicken and its mechanisms in rats. A chicken diet showed a strong thermic effect after consumption, and the removal of fat induced more rapid and stronger thermogenesis. Although thermogenesis induced by a purified chicken protein diet was also strong, the thermic reaction was not so rapid and a remarkable rise of peripheral temperatures was not observed. Defatted chicken and purified chicken protein activated the thyroid hormone system and up-regulated rate-limiting enzyme genes of glucose metabolism and the tricarboxylic acid (TCA) cycle in the liver. Moreover, chicken protein up-regulated the mRNA expression of a rate-limiting enzyme of hepatic lipid metabolism. It is possible that the mechanisms by which body temperature is raised are different between chicken protein and defatted chicken. On the other hand, it is possible that chicken fat suppressed the expression of energy metabolism-related genes that was induced by the consumption of lean chicken. As a result, a rise of postprandial body temperature might not have been induced after consumption of chicken fat. These results suggest that the consumption of lean chicken activates the thyroid hormone system and hepatic energy metabolism and consequently induces the postprandial thermic effect of chicken.

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.

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