Dietary fat saturation and cholesterol and fatty acid synthesis in aging rats

Abstract

Male and female rats were fed 40% of calories as beef tallow (BT) (polyunsaturated to saturated (P:S) fatty acid ratio = 0.17) or a mix of safflower oil and beef tallow to give a P:S of 0.94 (M) in a nutritionally complete diet. Groups were killed at 9, 12, 15, 18, and 21 months of age and fatty acid and cholesterol concentration and synthesis in liver in vivo were measured. Serum cholesterol concentration and appearance of newly synthesized lipid were also determined. Serum cholesterol concentration increased with age regardless of diet. Fatty acid synthesis from alanine was generally similar to that reported for acetate in response to variables, being higher in females than males and in males consuming BT diet than those consuming M diet. Cholesterol synthesis from alanine was similar to that reported from acetate with regard to sex effect (females higher than males), but did not differ in response to diet. The latter is contrary to reports for acetate incorporation, which has been higher for more polyunsaturated dietary fats. Female rats exhibited very high rates of incorporation of alanine into both fatty acids and cholesterol at 12–18 months of age when they were fed beef tallow. This effect was not observed in females fed mixed fat nor in males. The 21 month old BT females had alanine incorporation rates more like the rats at early ages. This decline at advanced age may be the result of death of those with high synthesis rates and survival of those with lower rates.