COMPARISON OF THE EFFECTS OF A RANGE OF DIETARY LIPIDS UPON SERUM ANDTISSUE LIPID-COMPOSITION IN THE RAT

Since the type of fat consumed in the diet may play a role in the deve lopment of several disorders, it is important to ascertain the effects of different dietary fats upon parameters such as serum lipid levels and adipose deposition. The aim of this study was to determine the eff ects of feeding rats a range of fats with differing fatty acid composi tions. Weanling male rats were fed for 10 weeks on a low fat (LF) diet or on one of five high fat diets, which contained 20% by weight of ei ther hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO ), evening primrose oil (EPO) or menhaden (fish) oil (MO). Food intake , animal growth, tissue weights at sacrifice, serum and liver lipid co ncentrations and serum, heart, brain and adipose tissue fatty acid com positions were studied. The food intake of the LF-fed animals was grea ter than that of animals fed on the high fat diets; there were no diff erences in food intake between animals fed the high fat diets. The tot al energy intake was lower for animals fed on the HCO diet than for th ose fed on the LF, OO, EPO or MO diets; there were no other difference s in energy intake between the groups. Animals fed the different diets had almost identical rates of weight gain up to 5 weeks; after this p eriod of rapid growth, the increase in weight was slower in all groups but especially in the LF-fed animals. The LF-fed rats had a lower tot al weight gain and smaller final weights than rats fed on the high fat diets. Animals fed on the MO diet had a greater weight gain than thos e fed on the OO or EPO diets and their final weights were greater. The MO diet resulted in greatly increased liver weight compared with each of the other diets. The HCO, OO and EPO diets also increased liver we ight compared with the LF diet. The total lipid content of the livers from rats fed the high fat diets was greater than that of those from r ats fed the LF diet; the livers from animals fed the MO diet contained more lipid than those from animals fed each of the other diets. MO fe eding increased the free cholesterol, cholesterol ester and triacylgly cerol contents of the Liver. Each of the high fat diets resulted in an increase in epididymal fat pad weight compared with the LF diet, but the high fat diets resulted in different degrees of adipose deposition ; the EPO and MO diets resulted in smaller epididymal fat pads than th e HCO, OO and SO diets. Serum total cholesterol concentrations were hi gher after feeding the OO, SO or EPO diets than after feeding the LF o r MO diets. The MO diet resulted in a total serum cholesterol concentr ation which was lower than that of animals fed each of the other diets . The serum cholesterol ester concentration of the MO-fed animals was lower than that of the LF-, SO- or EPO-fed animals. Serum triacylglyce rol concentrations of the HCO- and GO-fed rats were higher than those of the LF-, SO-, EPO- or MO-fed animals. The fatty acid compositions o f the serum, adipose tissue and the neutral lipid and phospholipid fra ctions of the heart reflected those of the diets themselves, apart fro m those from the HCO-fed animals, which contained much tower proportio ns of medium chain fatty acids than did the diet. The fatty acid compo sition of the phospholipid fraction of the brain was not affected by d ietary lipid manipulation. The fatty acid composition of the diet affe cts animal growth, tissue weights, serum cholesterol, cholesterol este r and triacylglycerol concentrations and the fatty acid compositions o f the serum, adipose tissue and heart. The fatty acid composition of t he brain is relatively resistant to dietary modification.