Molecular and cellular adaptations to carbohydrate and fat intake

Adaptation to carbohydrate and fat intake involves changes in a number of biochemical parameters at the cellular level. A change in the concentration of fat or carbohydrate in the blood acts directly to influence metabolic pathways by altering the flux of intermediates into cells. This in turn alters the concentration of hormones and other signaling molecules and changes the rate of expression of genes coding for key regulatory proteins or enzymes in metabolic pathways. These effects occur at different rates and in a tissue-specific manner in response to diet. A key metabolic adaptation involves changes in the level of expression of genes coding for proteins of critical importance in energy metabolism; this is largely due to an altered rate of transcription of selected genes under the control of hormones and/or carbohydrate and lipid. The mediators of this effect are transcription factors, that is, nuclear proteins which integrate the effects of hormones and substrates with the transcription process by binding to response elements in the promoters of regulated genes and interacting with the transcription machinery at the TATA box, thereby altering the activity of RNA polymerase II. In this review we will outline the hierarchy of cellular adaptations to diet and will emphasize the latest concepts of gene regulation in response to metabolites and hormones. In particular, we will review the role of the various transcription factors involved in the regulated expression of the gene for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.132), a key gluconeogenic enzyme.