Diurnal regulators of intestinal lipid absorption. Both food- and light-entrained oscillators appear to affect the expression of clock genes in the intestine. Intestinal clock genes affect other genes to modulate intestinal lipid absorption. So far, at least three proteins, MTP, apoAIV, and nocturnin, that affect diurnal variations in intestinal lipid absorption have been identified. Changes in the diurnal expression of these genes appear to affect diurnal variations in plasma lipids.