Protein Intake and Liver Cholesterol: Effects of Age and Growth of the Test Animal

Abstract

Rats were fed, from weaning, isocaloric control and cholesterol-rich diets containing, respectively, percentages of protein (casein and egg albumin) varying from 10 to 30. They were sacrificed after intervals varying between three and 12 weeks on diet. Several “single-run” experiments with older animals are summarized for comparison. Relationships between growth, food intake and liver lipid storage are discussed. Contról on cholesterol-free diets showed some decrease in liver cholesterol with increased percentages of dietary protein. Mean values varied from about 0.4% for those fed 10% of protein to 0.21 for the 30%-protein rats. With the exception of high values noted for rats fed 15 and 17% of protein at 7 weeks, changes with age were minor. Cholesterol-fed rats placed on a 15%-protein diet at weaning had the highest observed concentrations of liver cholesterol at about 7 to 8 weeks thereafter. At 10 weeks, liver cholesterols were much lowered. With 30% of protein, at three weeks after weaning, values were almost the same as for 15%. However, with the higher protein intake, liver cholesterol values fell rather than rose during the period of rapid preadolescent growth. With only 10% of protein, food intakes and growth rates were lowered. Liver glycerides were much higher than with 15% of protein, but liver cholesterol did not accumulate proportionately. Males fed 15% of protein with 0.07% of choline stored more liver cholesterol than females. With 10% of protein, sex differences were less marked. Protein was a less effective lipotropic agent in adults than in rapidly growing adolescents.