1. The influence of dietary carbohydrate, protein and lipid on the unconjugated hyperbilirubinaemia of Gunn rats has been studied.
2. In the first set of experiments, after a control period without restraint, the animals were restrained for 72 h and were either starved or received isocaloric amounts of glucose, protein hydrolysate or soya bean oil through a gastrotomy cannula.
3. A second study was performed with groups of unrestrained animals which were fed with diets supplemented with carbohydrate, protein and lipid for 7 days after a control period.
4. Both these studies showed that diets composed predominantly of carbohydrate or protein doubled the plasma bilirubin concentration. Starch, glucose and fructose produced similar effects.
5. A high-lipid diet in the absence of carbohydrate caused a slight reduction in plasma bilirubin concentration. This effect was observed with both soya bean oil and pork fat.
6. It has not been established whether the increase in hyperbilirubinaemia resulted from the high-carbohydrate content of the diet or the absence of lipid.